APHIS Evaluation of the Rhipicephalus 

(Boophilus) spp. Status of Sonora, Mexico

Animal and Plant Health Inspection Service

Veterinary Services, National Center for Import and Export

Regionalization Evaluation Services Staff

August, 2011
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Table of Contents

Abbreviations...................................................................................................................... 3

Executive Summary............................................................................................................ 5

Introduction......................................................................................................................... 8

Background......................................................................................................................... 9

Hazard Identification ........................................................................................................ 14

Release Assessment .......................................................................................................... 19

1. Authority, organization, and infrastructure of the veterinary services..................... 19

2. Rhipicephalus tick status of the region ..................................................................... 26

3. Rhipicephalus tick status of adjacent regions........................................................... 28

4. Extent of active tick control program ....................................................................... 31

5. Vaccination status of the region................................................................................ 36

6. Separation from adjacent regions of higher risk....................................................... 36

7. Movement controls and biosecurity from higher-risk regions.................................. 38

8. Livestock demographics and marketing practices in the region............................... 52

9. Tick surveillance in the region.................................................................................. 56

10. Diagnostic laboratory capacity ............................................................................... 58

11. Emergency response capacity................................................................................. 60

Conclusions................................................................................................................... 61

Exposure Assessment........................................................................................................ 63

Consequence Assessment ................................................................................................. 65

Risk Estimation................................................................................................................. 68

References......................................................................................................................... 69
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Abbreviations

AGL Asociaciones Ganaderas Locales (Local Cattlemen’s Associations)

APHIS Animal and Plant Health Inspection Service

CENAPA Centro Nacional de Servicios de Constatación en Salud Animal (National 

Animal Health Verification Services Center)

CENASA Centro Nacional de Servicios de Diagnóstico en Salud Animal (National 

Center for Diagnostic Services in Animal Health)

CFR Code of Federal Regulations

CFTEP Cattle Fever Tick Eradication Program

CIGAM Centros de Inspección de Ganado en Lugares de Alta Movilización 

(Centers of Livestock Inspection for High Movement)

CN Consumo Nacional (National Consumption)

CPA Comision Mexico-Estados Unidos para la prevención y control de la 

fiebre aftosa y otras enfermadades exoticas (Mexico-United States 

Commission for the Prevention of Foot-and-Mouth Disease and Other 

Exotic Animal Disease)

DGICA Dirección General de Inocuidad y Calidad Agroalimentaria (Agrofood 

Safety and Quality Control General Directorate)

DGIF Dirección General de Inspeccion Fitozoosanitaria (Animal and Plant 

Health Inspection Service General Directorate)

DGSA

DGSG

Dirección General de Salud Animal (Directorate of Animal Health)

Dirección General de Servicios Ganaderios (Director General of 

Livestock Services)

DINESA Dispositivo Nacional de Emergencia de Sanidad Animal (National Animal 

Health Emergency Operation) 

DIVE Dirección de Vigilancia Epidemiológica (Directorate of Epidemiological 

Surveillance)

GEESA Grupo Estatal de Emergencia en Salud Animal (State Animal Health 

Emergency Group)
4

NOM Norma Oficial Mexicana (Mexican Official Standards)

OIE Office International des Epizooties (World Organization for Animal 

Health)

PVI Puntos de Verificación e Internal (Internal Verification Post)

SAGARPA Secretaría de Agricultura, Ganadería, Desarollo Rural, Pesca Y Alimentación 

(Ministry of Agriculture, Livestock, Rural Development, Fishing, and Food)

SAGARHPA Secretaría de Agricultura, Ganadería, Recursos Hidraulicos Pesca y 

Aquaculture (Ministry of Agriculture, Livestock, Water Resources, Fisheries and 

Aquaculture)

SENASICA Servicio Nacional de Sanidad, Inocuidad y Calidad Agroalimentaria 

(National Service of Health, Safety and Quality Agrofood)

SINIIGA Sistema Nacional de Identificacion Individual de Ganado (National 

Individual Cattle Identification System)

UGRS La Unión Ganadera Regional Sonora (Sonora Regional Livestock 

Association)

USDA United States Department of Agriculture

VS Veterinary Services
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Executive Summary

In 2002, Mexico’s Ministry of Agriculture, Livestock, Rural Development, Fishing, and 

Food, Mexico (Secretaría de Agricultura, Ganadería, Desarollo Rural, Pesca Y 

Alimentación, or SAGARPA), officially requested that the United States Department of 

Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) review the 

Rhipicephalus (formerly Boophilus) annulatus and Rhipicephalus microplus tick status of 

the State of Sonora, Mexico. These ticks, known as cattle fever ticks, are the North 

American vectors for bovine babesiosis, or cattle fever. 

Upon receipt of this request, APHIS initiated an evaluation of the status of Sonora with 

regard to the Rhipicephalus spp. ticks named above. This report represents APHIS’ 

evaluation of Sonora with regard to the status, infrastructure, and control measures in 

place for Rhipicephalus spp. ticks and assesses the likelihood that these ticks could be 

imported into the United States via cattle and other susceptible livestock from Sonora. 

Supporting documentation used in this evaluation consists of information submitted by 

SAGARPA, site visit team observations during three site visits, information from the 

World Organization for Animal Health (OIE), peer-reviewed articles, and other technical 

sources. This risk analysis was conducted according to OIE guidelines and therefore 

includes a hazard identification section, a release assessment, an exposure assessment, a 

consequence assessment, and a risk estimate.

Release Assessment

Sonora has demonstrated that it has the infrastructure, personnel, and legal framework to 

prevent incursions of Rhipicephalus spp. ticks through its program of routine tick 

inspection and dipping during movement from areas at risk for tick infestation combined 

with strategic location of inspection stations along major transportation routes that enter 

into and traverse the State. Sonora’s transit guide system, which requires identification 

of livestock during movement and links tick inspection and treatment requirements to the 

origin and destination of livestock, ensures that appropriate control measures are applied 

to all livestock engaged in transit. This system, in combination with the annual livestock 

census, helps ensure that animals are not moved illegally thereby evading tick inspection 

and treatment procedures. An important component of Sonora’s successful control and 

eradication program is its Federal-State-private partnerships, which have been 

instrumental in accomplishing and maintaining Sonora’s Rhipicephalus-free status.

The desert-like climate in most of Sonora does not support the survival of Rhipicephalus 

tick spp. eggs. Consequently, this area, consisting of the northern and central portions of 

Sonora, has historically remained naturally free of Rhipicephalus spp. ticks. The 

southern tip of Sonora, near its border with Sinaloa, is more hospitable to these ticks, and 

occasionally experiences incursions. Delineations between the tick free area and the 

southern area (or buffer zone), are similar to those in place along the border between the 

U.S. permanent tick quarantine zone in South Texas and the rest of the United States. 
6

Four Rhipicephalus spp. infestations have been detected since eradication of this tick was 

declared in Sonora in 1972; however, all occurred exclusively within Sonora’s buffer 

zone, were detected before the infestation became widespread, and were contained and 

controlled within time frames established by SAGARPA. Movement controls and 

additional tick inspection and dipping requirements are in place for livestock that move 

from the buffer zone into the historically tick-free region of Sonora. These controls have 

been successful in restricting any incursions to the buffer zone.

If Rhipicephalus spp. ticks were to enter into Sonora, tick inspection requirements on 

premises and during movement could be expected to detect these ticks on Sonoran 

livestock. Surveillance efforts have proven effective at detecting tick incursions in the 

buffer zone in a timely manner. Surveillance for Rhipicephalus spp. ticks is multipronged and comprehensive, and includes routine surveillance through an integrated 

system of tick inspection tied to movement, an annual tick survey directed by 

SAGARPA, and active inspections in high risk areas within the buffer zone. 

Although APHIS has concerns about the delay in the turnaround time for acaricide 

analysis results from cattle dipping vats, Sonoran officials and inspectors demonstrate the 

willingness and ability to maintain appropriate acaricidal concentrations in the dipping 

vats. This factor, when combined with Sonora’s low environmental suitability for cattle 

fever ticks, excellent detection and response capabilities, and overlapping movement 

control procedures, results in the finding of a very low likelihood that Sonora would 

become infested with Rhipicephalus spp. ticks.

APHIS concludes that the likelihood that cattle imported from Sonora would introduce

Rhipicephalus spp. ticks into the United States is very low.

Exposure Assessment

APHIS assessed the likelihood of exposure of U.S. livestock to Rhipicephalus spp. ticks 

from cattle exported from Sonora to be low. The most likely route of introduction is 

through the legal importation of cattle. Successful exposure via this route would require 

that multiple steps take place in sequence following the importation of undetected 

Rhipicephalus-infested cattle into the United States, including the failure of tick 

inspections and any treatments applied at the U.S. border ports, transport of infested 

cattle to an environment suitable for tick survival and replication, and contact between 

the resulting larval ticks and domestic livestock populations. Because multiple, 

successive events would be required for the successful exposure of domestic livestock to 

Rhipicephalus spp. ticks as a result of the importation of infested cattle from Sonora, the 

likelihood of an exposure event is low. 

Consequence Assessment

The consequences of Rhipicephalus spp. ticks entering into the United States, resulting in 

a domestic infestation, would likely result in the implementation of a control campaign, 

which could be costly, especially if it becomes extensive. Costs of a single outbreak 
7

(defined as 3 infestations) in Texas were recently estimated at $123 million USD for the 

first year. If the outbreak expanded to the U.S. historic Rhipicephalus spp. tick range, 

cost estimates increased substantially, to $1.2 billion USD. 

If the tick infestation resulted in a resurgence of bovine babesiosis in the indigenous 

cattle population, the additional consequences could be expected to be significant, with 

morbidity rates of up to 50% and mortality rates in excess of 90% in affected cattle. 

Additionally, movement restrictions within the United States, as well as export trade 

losses, could be expected to add to these consequences.

Risk Estimation

In summary, although the consequences of an outbreak of Rhipicephalus spp. ticks in the 

U.S. cattle population could be costly, especially if associated with bovine babesiosis, 

APHIS considers the likelihood of Rhipicephalus-infested cattle entering the United 

States from Sonora resulting in exposure to U.S. cattle to be very low. 
8

Introduction

Rhipicephalus microplus and Rhipicephalus annulatus ticks1 are important because they 

are the North American vectors for bovine babesiosis, or cattle fever. Before this disease 

was eradicated from the United States (with the exception of the quarantine zone along 

Texas’ southern border with Mexico) in the 1940s it resulted in significant economic 

losses due to decreased productivity of cattle and movement restrictions both within and 

outside of the United States. 

The United States received a request for recognition of Sonora, Mexico as free of 

Rhipicephalus spp. ticks in 2002. Since then, Mexico has provided additional 

information from Sonora regarding its ability to prevent the entry of these ticks, detect 

them if they occur, and eradicate any infestations should they occur. In addition, APHIS 

has conducted three site reviews in Sonora, in 2002, 2006, and 2011, to evaluate

procedures associated with their tick control program. 

Current U.S. regulations, contained in the Title 9 of the Code of Federal Regulations 

(9CFR) in section 93.427 and expanded upon in Veterinary Services Memorandum No. 

591.69, require that cattle from Mexico offered for entry into the United States receive a 

“scratch” inspection by an inspector employed by the APHIS. A scratch inspection is a 

visual and hands-on inspection of cattle, with emphasis on the preferred tick attachment 

sites such as the neck, dewlap, and axillary region for the presence of ticks. If cattle are 

found to be free from ticks, they will be given one acaricide2 dipping treatment on the 

Mexican side of the border port, in the form of an immersion bath3

, and then allowed to 

cross into the United States. If cattle are found to be infested with Rhipicephalus spp. 

ticks, the entire lot of cattle will be rejected, dipped, and held in quarantine on the 

Mexican side of the border under the supervision of the inspectors at the port. After 10 to 

14 days the cattle will be inspected again, dipped, and then allowed to cross through the 

border port to the United States if no ticks are found.

 1 Rhipicephalus microplus and Rhipicephalus annulatus ticks were formerly referred to as Boophilus 

microplus and Boophilus annulatus, respectively. Due to morphological similarities, the two Boophilus

species became part of the Rhipicephalus genus of ticks. Subsequently, they will be referred to 

individually as Rhipicephalus microplus or Rhipicephalus annulatus or together as Rhipicephalus spp. ticks 

or cattle fever ticks (because they are both vectors for bovine babesiosis or cattle fever) in this document. 

Other, non-cattle fever tick species of Rhipicephalus ticks will be referred to by their full name. The term 

Boophilus will be retained when referring to official titles of programs, regulations, or documents.

2 Acaricides are pesticides that kill (or interrupt the life cycle of) ticks or mites. For the purposes of this 

assessment, acaricide will refer to chemicals used in the treatment of livestock for ticks and acaricidal 

solution will refer to those chemicals maintained in solution in cattle dip vats.

3 An immersion bath consists of a narrow tank filled with an acaricidal solution that is used to fully 

immerse cattle in order to treat or prevent infestation with ticks. Corrals and chutes are used to move cattle 

into and through the baths. The immersion bath is generally located below ground level, with cattle 

descending a ramp into the bath, swimming through the solution, and ascending another ramp at the end, 

re-emerging at ground level. Immersion baths may also be referred to as dip vats, dipping vats, or dip 

baths.
9

APHIS proposes to amend this section of the CFR to allow eligible cattle from Sonora to

be excluded from the dipping process when presented at land border ports of entry into 

the United States from Sonora. However, scratch inspections will be conducted on 

individual animals prior to entry into the United States.

Cattle and other livestock will still be required to be accompanied with certification by an 

official veterinarian employed by SAGARPA that the animals have been inspected and 

found visibly free from fever ticks and any evidence of communicable disease, and that, 

as far as it is possible to determine, they have not been exposed to splenetic, southern, or 

tick fever, during the 60 days immediately preceding their movement to the port of entry. 

Recognizing Sonora as free of Rhipicephalus spp. ticks and exempting Sonoran cattle 

from acaricide dipping at the port will facilitate trade with Sonora by minimizing 

economic costs associated with dipping procedures at U.S. ports. Additionally, the 

potential hazards to people and animals associated with the exposure to acaricides will be 

reduced, as will the additional time required to complete the dipping process at the U.S. 

ports of entry. 

Background 

History and control of bovine babesiosis and Rhipicephalus spp. ticks in the United 

States

The presence of bovine babesiosis in the southern United States in the late 19th and early 

20th century cost the U.S. cattle industry not only through production losses resulting 

from clinical disease, but also because of market exclusion from northern, disease-free 

U.S. States and export to other countries. These losses led to the creation of the Cattle 

Fever Tick Eradication Program (CFTEP) in 1906, which was tasked with the goal of 

eradicating the tick vectors responsible for transmitting bovine babesiosis. The program 

targeted affected states, including Texas, Oklahoma, Arkansas, Louisiana, Mississippi, 

Alabama, Georgia, Florida, South Carolina, North Carolina, Virginia, Tennessee, 

Kentucky, Missouri, and southern California[1] (see Figure 1). 

Figure 1. Distribution of Rhipicephalus spp. ticks in the United States (in blue) during

the early 1900s.
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Source: [2]

The eventual eradication of Rhipicephalus annulatus and R. microplus ticks and their 

associated diseases from the continental United States was achieved through a centrally 

planned and coordinated program that combined quarantine, mandatory dipping of cattle, 

surveillance, and pasture rotation. The campaign began at the northern perimeter of the 

infested zone and moved south. Although planning occurred at the central level, the

CFTEP was an example of one of the first cooperative State-Federal eradication efforts, 

benefitting from and ultimately succeeding due to strong producer buy-in [3, 4]. 

By 1943, the eradication campaign had been almost entirely completed; however, a small

area remained along the Rio Grande in south Texas in which ticks were unable to be 

completely eradicated due to this region’s proximity to areas in Mexico containing the 

ticks. This area is referred to as the permanent quarantine zone or buffer zone. It 

currently consists of a strip of land approximately 500 miles long extending from Del Rio 

to Brownsville, Texas which ranges from 123 yards to 8 miles in width (the area between 

the red line and the Mexican border depicted in Figure 2) [5-7]. 

Figure 2. Permanent tick quarantine zone, 2006.
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Source: [5]

Many of the activities that were used in the United States to eradicate ticks under the

CFTEP are currently employed as control measures in the permanent quarantine zone. 

Current efforts focus on surveillance by State and Federal CFTEP personnel, including 

approximately 85 mounted patrol inspectors known as “tick riders.” Tick riders patrol 

livestock premises within the buffer zone, conduct inspections and tick treatments for 

cattle moving within and out of the quarantine zone, perform trace-out and trace-back 

investigations, conduct surveillance for potentially tick-infested wildlife, maintain all 

program dipping vats, conduct inspections at selected livestock sale barns, and apprehend 

stray or illegal livestock crossing the Rio Grande [3, 7]. 

In addition, CFTEP officials inspect all native livestock being moved within or outside of 

the quarantine zone. Premises are placed under quarantine if even a single fever tick is 

found on a single animal within a herd. The duration of the quarantine ranges from 6-9 

months, depending on the time of year. By Texas state law, cattle under quarantine must 

be dipped every 7-14 days with an acaricide or removed from the infested pasture after 

two “clean” scratch and dipping treatments. In addition, cattle on all adjacent premises, 

as well as the herds of origin of cattle that have recently entered the herd or destination 

herds of those that have recently left, are inspected for the presence of ticks [3, 7-9].

Tick incursions or the threat of incursions in areas outside of the permanent quarantine 

zone in recent years have led to a temporary expansion of the quarantine zone. The 

detection of cattle fever ticks outside the permanent quarantine zone in 2007- 2009 led to 

the institution of temporary preventive quarantine areas adjacent to the permanent 

quarantine zone. Discrete sections of the temporary quarantine zones were lifted as 

surveillance and treatment measures as described above were satisfactorily completed in 

those areas [6, 10, 11]. 

The incursions were likely due, in part, to the maintenance of cattle fever ticks in wild

ungulates, especially white-tailed deer, which coexist in and around domestic cattle herds 
12

in South Texas and are known to be effective hosts for Rhipicephalus ticks. Additional 

factors were favorable weather conditions for tick harborage, the continued movement of 

stray and illegal cattle from Mexico, and U.S. resource shortages [5, 7]. 

In response to increasing fever tick infestations, several tactics are currently in use to 

combat ticks in the permanent quarantine zone and surrounding areas. These include the 

use of pasture management tools, feeders and neckbands designed to apply topical 

acaricides to white-tailed deer, and the use of treated feed for wild ungulates [5, 12, 13]. 

Several new developments, including research into new acaricidal drugs and treatment 

protocols, and vaccination programs against fever ticks, are also under investigation [12-

17]. Another mitigation measure being considered includes the Tick Control Barrier, an 

8-foot high game fence, along portions of the permanent tick quarantine line to prevent 

further unobstructed movement of tick-infested white-tailed deer and exotic ungulates 

into the free areas of South Texas [18, 19]. 

 

History and control of Rhipicephalus spp. ticks in Sonora

Sonora is located on Mexico’s northern border, south of Arizona and east of the Gulf of 

Mexico (Figure 3). Northern Sonora has historically remained free from Rhipicephalus

spp. tick infestation because of its inhospitable climatologic conditions (high altitude and 

desert-like conditions), although ticks have occasionally been found in the southern 

portion of the State referred to as the buffer zone because of its proximity to a tickinfested region of Sinaloa and southwestern Chihuahua. 

Figure 3. Map of Sonora, Mexico and surrounding area.

Source: http://www.map-of-mexico.org/mexico-states.gif

The campaign to officially eradicate Rhipicephalus spp. ticks from the entire State of 

Sonora formally began in 1932. The campaign was initiated by cattlemen who wished to 
13

gain freedom from these ticks for the entire State and approached the State government in 

order to gain regulatory and technical support to be able to do so [20]. 

In the beginning of the eradication effort, a zoosanitary (animal health) line was 

established, dividing Sonora into a clean (northern) and an infested (southern) region. 

Using a process of strict movement controls, which included a requirement to treat and 

inspect all livestock prior to movement from infested areas to clean areas, the line 

demarcating infestation was slowly pushed southward until the entire State was 

considered free of Rhipicephalus spp. ticks. As of November 1972, Sonora was officially 

declared free of these tick species by the Mexican government via a decree published in 

the Federation Official Diary (the equivalent of a U.S. Federal Register Notice) [20].

Although there have been occasional incursions of ticks into Sonora since its declaration 

of freedom from these ticks, all of the infestations were detected in Sonora’s buffer zone

and were quickly detected, thoroughly investigated, and successfully resolved within 

required time periods [20].

The Government of Mexico currently considers the entire States of Sonora, Baja 

California, Aguascalientes, and Tlaxcala, along with the Federal District, as areas entirely 

free of Rhipicephalus spp. ticks. Presumably, the absence of vector ticks in these states 

also gives rise to Babesia-free cattle populations. States in Mexico that are partly free of 

these ticks include Baja California Sur, Chihuahua, Coahuila, Nuevo Leon, Tamaulipas, 

Durango, Zacatecas, the plateau of San Luis Potosí, Guanajuato, Hidalgo, Federal 

District, and Puebla [21, 22]. However, APHIS has not yet evaluated any of these states 

and currently does not recognize them as tick-free (Baja California is currently under 

evaluation) [23]. 

Figure 4, below, displays a map of Mexico’s tick status according to the National 

Campaign against Rhipicephalus spp. ticks as of April 2011. The green Free Zone 

(Libre) is a geographical area that has been determined to be free of Rhipicephalus spp.

ticks by Campaign eradication activities or natural climatic conditions. The yellow 

Eradication Zone (Erradicación) is a geographical area in which a system of tick 

treatments, movement controls and surveillance activities aimed at total elimination of 

Rhipicephalus spp. ticks is practiced, requiring treatments of 100% of susceptible animals

for ticks. The red Control Zone (Control) is a geographical area with strategic and 

targeted tick treatments and surveillance aimed at reducing the number of Rhipicephalus

spp. ticks and the percentage of infected animals [22, 24]. 

Figure 4. Status of the National Campaign against Rhipicephalus spp. ticks, Mexico, 

April 2011.
14

Source: [22]

Hazard Identification

Hazard identification involves identifying the pathogenic agent(s) in animals or animal 

products which could potentially produce adverse health effects associated with its 

importation into a region [25]. In this assessment, the identified hazards (disease agent of 

concern) are the two protozoan organisms, Babesia bovis and Babesia bigemina. 

However, the assessment itself is focused on the eradication of the tick vectors for these 

two organisms, Rhipicephalus microplus and Rhipicephalus annulatus. These vectors are 

integral in the maintenance of Babesia infection in cattle, and elimination of the vectors 

is the mode of disease eradication used in the affected region under discussion. 

Bovine Babesiosis

Bovine babesiosis, known variously by such names as piroplasmosis, Texas fever, cattle 

fever, redwater, or tick fever, is a febrile disease of cattle caused by tick-borne 

intraerythrocytic protozoan parasites of the genus Babesia. The disease is widespread in 

the subtropics and tropics, where, historically, it has had serious economic impact on 

cattle production. Six different species of Babesia are known to infect cattle; the most 

significant species for cattle in the Western hemisphere are Babesia bovis and Babesia

bigemina. Babesia spp. are transmitted primarily by ixodid (hard-bodied) ticks [26, 27].

Etiology
15

Babesia spp. are protozoan parasites that invade red blood cells. Babesia bigemina

characteristically appears within mature erythrocytes as two joined, pear-shaped bodies. 

Babesia bovis is smaller and pleomorphic; it is considered the more virulent of the two 

species.

Host range/Species affected

Cattle are the primary hosts for both B. bigemina and B. bovis; however, it is possible for 

other animals to maintain the infection. Buffalo have reportedly been infected with both 

organisms, but this is considered uncommon and unlikely to present a reservoir of 

infection. White-tailed deer (Odocoileus virginianus) can be infected with B. bigemina

and B. bovis; however, their overall role in the epidemiology of babesiosis, particularly in 

deer populations that coexist among domestic cattle, is currently unknown [26, 28]. 

Transmission

Bovine babesiosis is transmitted primarily through the bite of infected R. microplus and 

R. annulatus ticks. Ticks acquire their infections when they feed on infected cattle and 

can pass the parasites transovarially to their larvae. In the case of B. bovis, infection is 

transmitted to the cattle host by the larval stage of the tick, whereas with B. bigemina,

transmission occurs from the nymph or adult tick. Mechanical transmission by biting 

flies and contaminated fomites can occur; however, this is incidental and insufficient to 

maintain the disease in a population without competent tick vectors [26].

Incubation period

The incubation period is approximately 2-3 weeks for B. bigemina and slightly longer for 

B. bovis. However, since B. bovis is passed to the host during an earlier phase of the 

tick’s development than B. bigemina, the prepatent period for the two agents is roughly 

equivalent [26].

Clinical signs

Clinical manifestations of bovine babesiosis vary greatly, depending on host 

characteristics and the strain of the organism. Cattle of all breeds are susceptible to 

babesiosis, though it is apparent that Bos indicus breeds, such as Brahman, and their 

crosses are more resistant to both the Babesia organism and its tick vectors than 

European breeds of Bos taurus, such as Hereford or Angus. Calves rarely show clinical 

signs of infection; however, in adult cattle, the disease may be severe and mortality in a 

herd of naïve adult cattle may exceed 50% [26, 29]. 

Initial signs include fever, anorexia, and lethargy; affected cattle may separate from the 

herd and exhibit arched backs, roughened coats, and dyspnea. A drop in milk production 

and increased abortion rates are frequently noted in affected herds. As the disease 

progresses, lysis of erythrocytes results in anemia, which is evidenced by pale mucous 

membranes, hemoglobinemia, and hemoglobinuria. A neurological syndrome known as 

cerebral babesiosis develops in some animals, characterized by such clinical signs as 

incoordination, circling, or head pressing, and in terminal stages, convulsions or coma

[26, 27]. 
16

Babesia bovis is considered the most pathogenic cause of bovine babesiosis, as it kills 

more than half the susceptible cattle it infects. In contrast, only a relatively small 

proportion of B. bigemina cases are fatal, and central nervous system signs are less 

frequently seen with B. bigemina infections [30]. 

In the absence of exacerbating stress, many animals survive with or without treatment, 

though recovery from the anemia-induced weakness and loss of condition is often 

protracted. Cattle surviving initial infection with B. bovis or B. bigemina usually remain 

persistently infected but resistant to clinical disease following re-exposure to the same 

strain. While parasite levels in the persistently infected animals are often undetectable, 

ticks may still be capable of acquiring infection from them. Thus, persistently infected, 

but apparently healthy cattle are potentially important reservoirs for the natural 

maintenance of the parasite [26, 31-34].

Treatment

A number of drugs have been used to treat bovine babesiosis, but only imidocarb and 

diminazene are still in common use. In certain countries, such as the United States, the 

use of babesiacidal drugs is restricted or they may be commercially unavailable. Babesia

bovis, like other small Babesia spp., is more difficult to treat than B. bigemina and may 

require additional therapeutic rounds. Supportive treatment such as blood transfusions or 

anti-inflammatory medications can be life-saving for severely affected animals [27, 35].

Vaccination

Vaccination against Babesia using a live, attenuated strain of the parasite has been used 

in several countries, but is not generally used in either the United States or Mexico; the 

focus in these countries remains on eradication of the tick vector [27]. 

Rhipicephalus microplus and R. annulatus ticks

Rhipicephalus microplus and R. annulatus are hard bodied ticks that tend to infest a 

single animal over their lifetime. Although heavy infestation with either of these two 

ticks may lead to production losses and damage to hides, their primary importance is 

based on their status as the two North American tick vectors responsible for transmitting 

bovine babesiosis and anaplasmosis [8, 9]. 

Life cycle

Both R. microplus and R. annulatus are one-host ticks, meaning that all three stages -

larva, nymph, and adult – reside, feed, and mate on the same animal throughout their 

lifetime. The life cycle is completed when an adult female tick drops off the host to lay 

thousands of eggs in the environment and then dies. The eggs hatch in the environment 

and larvae crawl up grass or other vegetation to attach to a new host. The larvae are 

usually found on the soft skin along the brisket or inside the flanks, thighs, or forelegs. 

An immature tick molts twice after feeding, developing from larva into nymph and 

finally into the mature, adult stage. Each stage feeds only once over a period of several 

days. The entire life cycle of the tick is completed within 3-4 weeks once attached to a 
17

host; however, the ticks can live for up to 6 months in the environment while waiting to 

find a host [8, 9].

Naïve ticks acquire Babesia organisms during feeding on infected animals. The infection 

is then passed within the ovaries of a mature female tick to her eggs. The percentage of 

infected larvae produced by an infected female varies from 0% to greater than 50% and is 

dependent primarily on the level of parasitemia of the host animal [33].

Both temperature and relative humidity are key factors governing tick survival and 

establishment of viable populations of ticks. It has been shown that climatologic factors, 

including soil temperatures above 25°C or below 17°C and arid conditions reduces the 

viability of eggs and can break the transmission cycle of the tick. Air temperature also 

has an effect on the passage and development of Babesia parasites in the egg and larval 

stages of the host tick; development of the parasites within R. microplus and R. annulatus

appears to be inhibited at temperatures below 20o

C [36-41].

Hosts

Although R. annulatus prefers cattle hosts, the tick can occasionally be found on other 

hoofed animals, such as horses and deer, and rarely on goats and sheep. Rhipicephalus

microplus is found on a wider range of hosts, infesting cattle, buffalo, and deer, and 

infrequently, horses, donkeys, sheep, goats, and camelids [8, 9].

Geographic range

Rhipicephalus microplus, considered the most important parasite of livestock in the 

world, has been introduced from Asia to tropical and subtropical regions of Africa, 

Australia, Central and South America, Mexico, and the Caribbean. The range of R. 

annulatus is also widespread throughout the warmer regions of the world; originally from 

the Middle East and Mediterranean regions, the tick was probably imported with 

livestock from Spain during the early colonization of Mexico. Following outbreaks of 

Babesia bovis that resulted in devastating economic losses to the U.S. cattle industry,

both tick species were eradicated from the continental United States between 1906 and

1943. Today, a permanent quarantine zone remains along the border between Texas and 

Mexico, extending from Brownsville to Del Rio, to prevent reintroduction of the disease 

vectors into the United States. Both tick vectors remain prevalent in parts of Mexico [42-

45].

Extensive portions of Mexico as well as the southeastern United States have climates that 

could support the life cycle of Rhipicephalus spp. ticks infected with Babesia spp 

organisms. In Mexico, areas with suitable habitat include Veracruz, Tabasco, Chiapas, 

Quintana Roo, and the Yucatan Peninsula. Areas that are not conducive to tick survival 

and propagation include Baja California, Sonora, and a large patch in the central region 

of Mexico. Development of the tick and the parasite are inhibited by environmental 

temperatures less than 20o

C. In the U.S., mean annual temperatures below 20oC appear

north of latitude 36° N, which crosses the country near the northern border of Texas; 

thus, regions of the U.S. located below latitude 36o

N are more likely to have favorable 

environments to support establishment of populations of Rhipicephalus (=Boophilus)

spp. ticks carrying Babesia spp. parasites [37, 39, 40, 46, 47].
18

Control Measures

Treatment of cattle with pesticides by spray, dipping vat, or pour-on methods, lies at the 

center of most tick control and eradication campaigns, both for tick elimination as well as 

prevention of infestation. Control of Rhipicephalus spp. ticks in the continental United 

States, where these ticks have been eradicated from all states except the quarantine zone 

at the southern boundary of Texas, focuses on surveillance, movement controls, and tick 

treatments. Epidemiologic investigations are also conducted to trace sources of infection 

into an area and to evaluate for potential exposure to other herds. In areas where these 

ticks are found to exist, multiple control methods may be employed, including pesticide 

treatment, pasture rotation, environmental modification, and other integrated biologic and 

chemical control strategies [45, 48]. 

Resistance issues

All currently used pesticides for tick control, or acaricides, can be grouped in three main 

chemical classes: organophosphates, synthetic pyrethroids, and amidines. Over the last 

decade, Rhipicephalus spp. ticks in North America have been found to be resistant to the 

all three classes of acaricides used for control and eradication purposes. In Mexico, 

resistance to organophosphate acaricides first developed in the 1980s, and resistance to 

pyrethroids was subsequently discovered in the 1990s. Amitraz, an amidine acaricide, 

was introduced to control organophosphate-resistant ticks in Mexico in 1996; however, 

the first case of amitraz resistance from Mexico was confirmed in 2001 in R. microplus in 

the State of Tabasco. Acaricide resistance is now widespread throughout Mexico; cattle 

fever ticks resistant to one or more classes of chemicals have been found in at least 15 

Mexican states. Results from a 2007 survey conducted in Mexico revealed that less than 

10% of ticks surveyed were susceptible to all three acaricides while approximately 40% 

were resistant to all three. Chemical resistance in Rhipicephalus spp. ticks has not been 

reported in Sonora [49-52].
19

Release Assessment

A release assessment describes the biological pathway(s) necessary for an importation 

activity to introduce pathogenic agents of animal health into a particular environment and 

estimates the probability of that introduction [25]. This release assessment addresses the 

11 factors described under 9 CFR 92.2 for the evaluation of foreign animal disease status. 

APHIS evaluated the current status of Sonora, Mexico with regard to Rhipicephalus spp.

ticks to decide whether it can recognize Sonora as free of Rhipicephalus spp. ticks. 

Those factors are:

1. The authority, organization, and infrastructure of the veterinary services 

organization in the region.

2. Disease status.

3. The status of adjacent regions with respect to the agent.

4. The extent of an active disease control program, if any, if the agent is known to 

exist in the region.

5. The vaccination status of the region.

6. The degree to which the region is separated from adjacent regions of higher risk 

through physical or other barriers.

7. The extent to which movement of animals and animal products is controlled 

from regions of higher risk, and the level of biosecurity regarding such 

movements.

8. Livestock demographics and marketing practices in the region.

9. The type and extent of disease surveillance in the region.

10. Diagnostic laboratory capacity.

11. Policies and infrastructure for animal disease control in the region, i.e., 

emergency response capacity. 

1. Authority, organization, and infrastructure of the veterinary services 

Sonora’s Rhipicephalus spp. tick monitoring and control program is based on an 

integrated system of organizations and laws that regulate the movement of livestock into, 

out of and within Sonora. It requires tick inspection and treatment of livestock (including 

cattle, horses, sheep and goats) at strategically placed inspection stations located 

throughout Sonora. Livestock entering Sonora from the neighboring Mexican States of 

Chihuahua and Sinaloa are required to be inspected for ticks and treated with an 

acaricidal solution by official inspectors, as are those that are moved within or out of 

Sonora’s tick buffer zone. (Livestock transiting Sonora from Baja California are 

exempted from dipping and will be discussed later.) The buffer zone is comprised of 

portions of Álamos, Navojoa, Huatabampo and Etchojoa municipalities, and is located 

along Sonora’s southern border (see figure 5). This area is considered to be at relatively 

high risk for Rhipicephalus tick incursions based on its proximity to areas that are 

currently infested with these ticks [53]. 
20

Figure 5. Tick buffer zone in southern Sonora (green shaded area)

Source: [54]

Legal Authority

The legal framework for Sonora’s Rhipicephalus tick surveillance, monitoring, and

eradication activities are formed by different layers of overlapping legislation. 

Mexico’s Federal Law on Animal Health (Ley Federal de Salud Animal) outlines the 

authorities of the Federal government in the implementation, enforcement and monitoring 

of animal health programs throughout Mexico, including the National Tick Eradication 

Campaign. It provides a regulatory framework for the use of measures to protect animal 

health, including animal health certificates, movement restrictions, and inspection 

procedures at international and domestic inspection points. It also provides the 

authorization for the administration of tick dipping and inspection stations [55].

Federal Laws provide the framework for regulations contained in the Normas Oficiales 

Mexicanas (NOMs). NOMs are analogous to the regulations within the U.S. Code of 

Federal Regulations. All regulatory actions are publically available and published in the 

Federal Official Newspaper or Diario Oficial de la Federacion. 

NOMs created from the Federal Law on Animal Health stipulate the rules and procedures 

for federal animal health programs. The primary Federal regulation governing the 

National Tick Eradication Campaign is NOM-019-ZOO-1994 (National Campaign 

against the Tick or Campaňa Nacional contra la Garrapata Boophilus spp.). NOM-019-

ZOO-1994 outlines specific provisions related to the Rhipicephalus tick control and 

eradication program in Mexico. One of its general provisions is the institution of 
21

movement restrictions in order to protect the tick-free status of States or regions. It also 

includes specific information on the measures to be employed at different stages of the 

tick eradication program, acceptable diagnostic tests for ticks and tick-borne diseases, the 

appropriate administration of acaricide treatments, general acaracide management 

principles for both dipping vats and spray equipment, appropriate quarantine measures in 

the event of an incursion, cleaning and disinfection requirements for vehicles transporting 

infested livestock, and movement requirements for livestock moving between zones with 

different tick status [24, 56, 57].

Several other NOMs are indirectly involved in the control of ticks, providing guidance 

and regulations for the movement of livestock and their products, quarantine procedures, 

animal health inspection points, epidemiological surveillance, and acaricidal efficacy

testing, among other things.

State regulations governing tick-related activities include Sonora’s Livestock Law (Ley 

de Ganaderia para el Estado de Sonora), which spells out requirements for the

importation of livestock into Sonora as well as information on the assignment, 

organization, and duties of livestock inspectors, movement requirements and penalties for 

noncompliance. It also provides specific guidance on the application of quarantines and 

notification in the event of Rhipicephalus tick incursions and lays out the penalties for 

non-compliance. In addition, Sonora also maintains an operational manual that provides 

detailed guidance on tick inspection and treatment procedures, recordkeeping 

requirements, documentation review, sample collection, and acaricidal solution 

management [20, 58]. 

There are also phytosanitary (plant health) requirements and standards that regulate the 

importation of crop products that may contain Rhipicephalus spp. ticks, including alfalfa, 

oats, barley, corn, hay, sorghum, wheat, and grass into tick-free areas [56].

Federal Animal Health Authorities

The Ministry of Agriculture, Livestock, Rural Development, Fishing, and Food 

(Secretaría de Agricultura, Ganadería, Desarrollo Rural, Pesca, y Alimentación, or 

SAGARPA) is Mexico’s Federal agency responsible for oversight and regulation of

agriculture, including animal health programs such as the National Tick Eradication 

Program. SAGARPA is the counterpart to the United States Department of Agriculture.

Within SAGARPA, the National Service of Food Health, Safety, and Quality (Servicio 

Nacional de Sanidad, Inocuidad y Calidad Agroalimentaria, or SENASICA) is 

responsible for the oversight of animal and food health and safety issues. SENASICA is 

the equivalent of USDA’s Animal and Plant Health Inspection Service (APHIS) and is 

responsible for coordinating the implementation and oversight of the Federal Law on 

Animal Health and its NOMs at the Federal and State levels.

Within SENASICA, there are three agencies involved with animal health issues: the 

Directorate of Animal Health (Dirección General de Salud Animal, or DGSA), the 

Animal and Plant Health Inspection Service General Directorate (Dirección General de 
22

Inspeccion Fitozoosanitaria, or DGIF), and the Agrofood Safety and Quality Control 

General Directorate (Dirección General de Inocuidad y Calidad Agroalimentaria, or 

DGICA) [59]. 

The DGSA oversees the animal health campaigns (campañas zoosanitarias) including 

control and eradication measures for Rhipicephalus spp. ticks. The Chief Veterinary 

Officer of Mexico heads the DGSA and overseas several animal health divisions that 

provide support for the activities for the prevention and eradication of ticks in livestock, 

including the Directorate of Epidemiological Surveillance (Dirección de Vigilancia 

Epidemiológica, or DIVE), the Directorate of Animal Health Campaigns (Dirección de 

Campañans Zoosanitarias), and the Directorate of Import, Export, and Livestock 

Services and Certification (Dirección de Importación, Exportación, Servicios y 

Certificación Pecuaria). Additionally, the animal health activities of DGSA are 

supported by the Mexico-USA Commission for the Prevention of Foot-and-mouth 

Disease and other Foreign Animal Diseases (Comision Mexico-Estados Unidos para la 

prevención y control de la fiebre aftosa y otras enfermadades exoticas, or CPA) and two 

national reference laboratories, the National Center for Diagnostic Services in Animal 

Health (Centro Nacional de Servicios de Diagnóstico en Salud Animal, or CENASA) and 

the National Animal Health Verification Services Center (Centro Nacional de Servicio de 

Constatación en Salud Animal, or CENAPA). CENAPA serves as the official national 

reference laboratory for both tick identification and acaricide evaluation [59, 60].

State Animal Health Authorities

Animal health programs in Sonora, including tick programs, are conducted under an 

interwoven network of authorities and resources. Each State contains a Federal 

SAGARPA delegate and other Federal personnel under the delegate who are responsible 

for certain animal health programs. Examples of activities under the authority of both 

SAGARPA and State officials include quarantine and movement restriction, accreditation 

of professionals to perform official program activities, implementation and enforcement 

of reporting requirements for specific diseases, establishment of an emergency animal 

disease response network, provision of diagnostic services, including reference services

and confirmatory diagnosis, and depopulation of affected and exposed animals [54].

The State of Sonora’s animal health authority rests within its Ministry of Agriculture, 

Livestock, Water Resources, Fisheries and Aquaculture (Secretaria de Agricultura 

Ganaderia Recursos Hidraulicos Pesca y Aquaculture, or SAGARHPA). Within 

SAGARHPA, the Director General of Livestock Services (Dirección General de 

Servicios Ganaderios, or DGSG) oversees livestock programs, including inspection, 

registration, quarantine stations, and animal health issues [60, 61]. 

Local Animal Health Authorities

The livestock zone is the basic operational unit for control of livestock movement and 

health in Sonora. Sonora is comprised of 72 municipalities which are in turn divided up 

into 482 livestock zones in all (see Figure 6 for a map of Sonoran municipalities) [20].

Figure 6. Map of Sonora’s municipalities.
23

Source: [62]

Each livestock zone is under the authority of a livestock inspector, who has primary 

responsibility for official livestock activities within his or her zone. There is also a 

backup livestock inspector for each zone. The activities and authority of the livestock 

inspectors are provided in Sonora’s Livestock Law. Livestock inspectors are private 

individuals who reside in the livestock zone for which they are responsible. They are 

appointed by the DGSG based on a nomination from the Local Cattlemen’s Association, 

and are paid from user fees collected by the Association for movement, slaughter, and 

export of cattle. The position of livestock inspector is one of honor in the community, 

and nominations are based on the inspector’s knowledge of livestock, knowledge of their 

zone, and their moral character within the community. The inspector must have at least a 

secondary education and lived in the community for at least two years. There are 486 

livestock inspectors in Sonora, 64 of which are located in the buffer zone [20, 58]. 

Livestock inspectors are responsible for many animal health activities, including issuing

and cancelling transit guides for all livestock producers within their zone. Livestock 

inspectors also maintain and enforce quarantines when necessary. If Rhipicephalus spp. 

ticks are detected in a herd, a quarantine of the originating premises will be authorized by 

either State or Federal sanitary authorities and overseen by the livestock inspectors. 
24

Additionally, livestock inspectors are responsible for conducting the annual inventory of

all livestock, delivering identification tags, and counseling producers on livestock 

program issues for all premises in their zone. They are ultimately responsible for 

identifying and regulating the movement of all livestock within their assigned livestock 

zone [20, 54, 63].

Oversight of livestock inspectors is provided by 10 regional supervisors, each of whom 

oversees 40-45 livestock inspectors. As with the livestock inspectors, the supervisors are 

also appointed by the SFG, but unlike the livestock inspectors, the supervisors are paid by 

the State of Sonora. The regional supervisor is responsible for providing training, 

supervision, and guidance for livestock inspectors within their area, and also reviewing

and following up on movement documents, inventory reports, and quarantine documents 

issued by the inspectors to make sure that the documents are complete and that 

appropriate actions were taken. The supervisors communicate with officials in the 

DGSG, providing a monthly report of all livestock activities within their jurisdiction [20, 

54, 60].

In addition to the livestock inspectors and their supervisors, Sonora also directly employs 

approximately 50 inspectors at 12 Centers of Livestock Inspection for High Movement 

(Centros de Inspección de Ganado en Lugares de Alta Movilización or CIGAMs). These 

high movement centers are located around areas near border crossings and corrals for 

livestock assembly and/or export. The inspectors at these centers primarily issue and 

cancel movement documents (i.e. transit guides) for livestock moving in and out of their 

affiliated facilities. In doing so, they verify that all documentation is present and 

appropriate to the intended movement, that seals are intact, and identification numbers 

and brands of the animals match those listed in the documentation. They also provide a 

brief health inspection (visual), and check that animals intended for export have received 

the proper tests and are appropriately tagged. They also confirm that animals originating 

from the southern part of the state are accompanied by tick dipping certificates. If 

necessary, they may serve as backup inspectors for livestock inspectors in their livestock 

zone [54].

Livestock Industry Partnerships

Private cattlemen’s groups have been instrumental in eradication and continual exclusion 

of Rhipicephalus spp. ticks from Sonora. The Regional Cattlemen’s Union of Sonora (La 

Unión Ganadera Regional de Sonora, or UGRS) is composed of 83 local cattlemen’s 

associations (Asociaciones Ganaderas Locales, or AGLs), and includes 35,000 active 

members representing approximately 95% of cattle producers in Sonora. This group 

spearheaded the eradication campaign and organized the first request to recognize Sonora 

as tick-free to SAGARPA, with the ultimate goal of being recognized by the U.S. 

government as tick-free, and to potentially eliminate the tick dipping requirement for 

Sonoran cattle exported to the United States [20]. 

The AGLs provide oversight of tick dipping procedures at the line dipping vats, in the 

buffer zone (the line dipping vats consist of a string of strategically placed dipping vats 

within the buffer zone). The presidents of the AGLs from the three municipalities that 
25

make up the buffer zone are the leaders of the Dipping Vat Operative Subcommittee (the 

Committee). The Committee operates under a joint agreement between the UGRS, 

SAGARPA, the State of Sonora, and the AGLs of the three municipalities that make up 

the majority of the buffer zone. The Committee provides operating guidelines and 

general oversight of the tick program, while the AGLs are responsible for ensuring that 

dipping and inspection procedures conducted in the buffer zone are adequate. 

SAGARPA provides the technical standards, operating personnel for programs, 

monitoring and inspection, financial and physical resources. The State of Sonora 

provides training, personnel, and performs movement control activities, as well as 

contributing financial and physical resources. The UGRS provides the remaining funding 

as well as dissemination of information and promotion of activities to be employed by 

producers in order to comply with all measures. And the AGLs agree to make their cattle 

and land available for treatment and inspection, and also promote and disseminate 

information about the program [20, 54]. 

The State of Sinaloa also works with Sonoran officials and AGLs from both States in 

order to conduct control activities in premises near or on the border between Sinaloa and 

Sonora [54].

Similarly, members of AGLs from livestock zones bordering the State of Chihuahua also 

cooperate with the Sonora officials in the maintenance and staffing of the zoosanitary 

cord, which helps to ensure the inspection of every animal that crosses the border into 

Sonora from Chihuahua. The zoosanitary cord consists of a number of inspection 

stations along the border with Chihuahua. Each is owned and maintained by the AGLs of 

the municipality in which the facility is located. Technical guidance and oversight of the 

facilities is provided by State officials while on-site operations are managed by the 

livestock inspectors for each respective livestock zone [20]. 

The AGLs also work with State and Federal sanitary authorities on other disease 

eradication efforts, such as tuberculosis and brucellosis [20]. 

Discussion

The overlapping system of laws and agencies used by Sonora to maintain programs and 

staff for identification, movement control, and tick surveillance, inspection, and 

treatment, provides significant assurance that these activities are carried out effectively 

by personnel. 

The movement control system, in combination with identification requirements, tick 

inspections, and check stations, appears to be very effective at tracking movement of 

livestock and assuring that appropriate treatments and inspections are provided. 

Sonora has the legal authority to enforce both Federal and State Rhipicephalus tick 

eradication regulations, and the personnel and infrastructure necessary to carry out 

livestock movement control activities. Site visit teams were impressed with the overall 

knowledge and professionalism of the staff and field personnel, in particular those at the 

dipping and quarantine stations. In addition, compliance with identification, inventory, 
26

inspection, treatment, and movement requirements by livestock producers in Sonora 

appears very high. The active participation of the Local and State Cattlemen’s 

Associations with government animal health programs appears to work well in 

maintaining Sonora’s tick-free status. 

2. Rhipicephalus tick status of the region

The State of Sonora was declared free from Rhipicephalus spp. ticks by the Mexican 

government on November 27, 1972, via a decree published in the Federation Official 

Diary [20].

Historically, the northern region of Sonora has not been subject to infestation with

Rhipicephalus spp. ticks due to its warm, dry climate and high altitude. However, these

ticks were present in the southern portion of Sonora, which has a climate that is more

amenable to Rhipicephalus and other tick species. In an effort to eradicate these ticks

from the entire State of Sonora, hopefully leading to fewer export restrictions, cattlemen 

from the southern region of the State combined their efforts for the first time, forming the 

Local Cattlemen’s Association, or AGL, in 1932. A private committee was formed 

specifically to coordinate all activities necessary to officially eradicate Rhipicephalus

ticks, which included requesting regulatory and technical support from State and Federal 

authorities in addition to providing personnel, money and motivation [20].

Initially, a sanitary line was established, dividing the State into two regions: clean

(northern) and infested (southern). Strict movement controls between the two regions

were imposed by the DGSA of SAGARPA, specifically a requirement that all livestock 

moving north from infected to clean regions receive a tick inspection and treatment. Tick 

dipping stations were placed at strategic locations along the sanitary line so that 

cattlemen with small operations could reach them on a regular basis in order to treat their 

cattle before moving them across the line (big ranches often had their own dipping bath 

facilities at that time). Bathing schedules and protocols for the use of acaricidal products 

were established, quarantine stations (which included tick dipping facilities) were created 

on the access highways leading into the State, and additional tick inspection and dipping 

stations were put in place along smaller roads leading into and across the State [20].

The campaign gradually advanced from north to south, increasing the area included in the

tick-free zone under the direction of the DGSA until 1972, at which point the entire State 

of Sonora was formally declared free of Rhipicephalus spp. ticks (with the recognition of 

the existence of a buffer zone adjacent to non-tick-free regions in northern Sinaloa and 

southwestern Chihuahua, which is equivalent to the U.S. permanent quarantine zone for 

ticks in South Texas). By 1972, no ticks had been found in Sonora for 10 years prior. At 

this point the authority and responsibility for maintenance of the tick-free status was

passed from SAGARPA to Sonora [20]. 

In order to verify freedom from Rhipicephalus spp. ticks, the Mexican government

required surveillance over a period of a year and a half, starting at the beginning of 

summer and extending through the end of the following summer. Surveillance activities 
27

consisted of on-farm inspections by official personnel every 14-21 days on every 

livestock premises in the proposed free-zone. The detection of any ticks during the 

surveillance period would mean treatment of all livestock in the proposed area, and 

restarting the surveillance clock. No ticks were found during the surveillance period for 

Sonora; therefore, at the conclusion of the surveillance, a notice was published for 

comment in the Federation Official Diary, and the area was declared free of 

Rhipicephalus spp. ticks [24].

Tick incursions into the buffer zone since 1972

Since eradication was declared in 1972, there have been instances of Rhipicephalus spp. 

re-infestations in Sonora, all entirely contained within the buffer zone, and specifically 

along the border with Sinaloa. Since the incursions were located entirely within the 

buffer zone, Sonora was not required to restart the treatment and surveillance cycle for 

the entire State. The affected premises plus neighboring premises were placed under 

quarantine for a year and a half (two summers with a winter season in between) during 

which time they underwent surveillance as described above. Additionally, any farms 

containing livestock that had moved into or out of infested farms (i.e. epidemiologically 

linked farms) were evaluated for the presence of ticks. If the epidemiologically linked 

farms were not found to be infested they were released from quarantine without having to 

undergo prolonged surveillance measures [20, 63].

Two of the tick incursions into Sonora occurred in the 1990s (1993 and 1998). These 

incursions were brought under control and eradicated in accordance with procedures 

established in the NOM-019-ZOO-1994, including treatment of all livestock on the 

affected properties and inspection of livestock on neighboring and epidemiologically 

linked properties, followed by an extended period of surveillance as described above. 

Following the successful completion of the surveillance period, which was conducted 

under the supervision of the DGSA, the State of Sonora regained its tick-free status [20]. 

On January 13, 2006, the local livestock inspector detected an infestation of 

Rhipicephalus microplus on four out of 48 cattle while inspecting a herd located in the 

Huatabampo municipality, within the buffer zone. Subsequent investigation identified 

the spread of the ticks to five additional farms, all within the buffer zone. This incident 

precipitated an emergency response involving quarantine and investigation of 

epidemiologically linked farms. Surveillance activities were conducted on all premises 

for the required time period with no additional ticks found, and all quarantines were

subsequently lifted. This infestation uncovered a deficiency in Sonora’s livestock 

movement system. It was determined that the infestation was allowed to spread to 

epidemiologically linked premises because there had been no requirement for livestock

moving exclusively within the buffer zone to be inspected and dipped for ticks prior to 

movement. Subsequent actions, including a new requirement for tick inspection and the 

use of transit guides (movement control documents) for livestock movement within the 

buffer zone, even if the animals were not entering the tick-free portion of Sonora, were 

implemented as a result of the finding and remain in place today. Additional training in 

emergency response and investigation, and enhancement of surveillance activities in the 

buffer zone were also enacted in response to the outbreak [63, 64]. 
28

Rhipicephalus microplus ticks were again detected in the buffer zone in October 2008 in 

80 head of cattle on a farm in the Alamos municipality. The incursion was determined to

be the result of movement of cattle onto the farm from a neighboring premises in the El 

Fuerte municipality of Sinaloa. The affected premises and adjacent premises were placed

under quarantine and all animals dipped with coumaphos4 and injected with ivermectin5

. 

Movement controls were established and regular inspections during the mandated 

quarantine period of one and one half years. No additional ticks were detected during 

this time, and the quarantine was subsequently lifted [54, 65]. 

Routine surveillance activities conducted throughout Sonora during 2009 identified four 

new farms with Rhipicephalus microplus infestation. Of 347 premises inspected in the

buffer zone during the 2009 systematic state-wide surveillance activities, Rhipicephalus 

microplus ticks were collected at four different premises, all located in the Alamos 

municipality, and all at or near the border with Sinaloa. Rhipicephalus microplus ticks 

were found on one animal out of 600 inspected on one farm on June 26, 2009; on three 

animals out of 475 on Dec. 2, 2009; on two animals out of 1,200 on Oct. 1, 2009; and on 

six animals out of 260 on Dec. 18, 2009. 

Livestock located on affected premises received an injection of ivermectin that is labelled 

as effective against Rhipicephalus ticks every 60 days. The first summer and winter 

inspections were conducted as part of the official surveillance activities by the Animal 

Health Campaign and Epidemiologic Surveillance Office of the DGSA, the DGSG of 

SAGARHPA, and the TB and Brucellosis Campaign Committee. No Rhipicephalus spp. 

ticks were found on any animals on the affected or adjacent farms (adjacent farms consist 

of 14 premises with 5,358 cattle total). 

Discussion

The operational measures used to maintain the Rhipicephalus free status of Sonora have 

been largely successful, as can be seen by the maintenance of this status over most of the 

State since 1972. When incursions have occurred within the buffer zone, they appear to 

have been identified prior to significant spread (with the exception of the 2006 outbreak, 

which led to identification and correction of deficiencies in Sonora’s tick control 

operations). In addition, control efforts, including movement controls (both general 

controls and enhanced controls aimed at quarantined premises) and repeated inspection 

and treatment for ticks on affected and associated premises, have been successful in 

preventing infestations from occurring outside of the buffer zone despite repeated 

incursions, which is similar to the situation in the U.S. permanent tick quarantine zone. 

3. Rhipicephalus tick status of adjacent regions

 4 Coumaphos is an organophosphate pesticide that is used in the control of ticks. Commercial formulations 

of coumaphos include Asuntol®, a product of Bayer Animal Health. 

5 Ivermectin is a broad spectrum antiparasitic agent that is available in many different formulations and is 

used in the control of ticks and other parasites. 
29

The western border of Sonora consists of the Gulf of California, while the northern edge 

is bordered by two U.S. States (Arizona and New Mexico), and the small northwestern 

tip adjoins Baja California. To the east is the State of Chihuahua and along the narrow 

southern border lies the State of Sinaloa (see figure 7).

Figure 7. Map of Sonora and surrounding areas.

Source: http://www.map-of-mexico.co.uk/images/sonoraenglish.gif

The U.S. States of Arizona and New Mexico are considered free of Rhipicephalus spp. 

ticks. 

Two of the three Mexican States surrounding Sonora are considered completely or 

partially free of Rhipicephalus spp. ticks by SAGARPA, although none have been 

officially declared free by APHIS to date. Baja California was declared free of

Rhipicephalus spp. ticks by the Mexican government in October 2007 [66]. SAGARPA 

considers the majority of Chihuahua to be free of these ticks, with two municipalities 

currently undergoing eradication and four still considered infested. The four non-tick 

free areas are located in southwestern Chihuahua, along its border with Sinaloa [21, 67]. 

Although neither Baja California nor Chihuahua is currently considered free of 

Rhipicephalus spp. ticks by APHIS, Baja California is currently under evaluation by 

APHIS regarding its tick status, and SAGARPA has requested a tick review of 

Chihuahua by APHIS [10, 23].
30

The majority of Sinaloa is currently considered by SAGARPA to be infested with 

Rhipicephalus ticks. Sinaloan officials are currently working with SAGARPA as well as 

Sonoran officials and local AGLs (in both Sonora and Sinaloa) in a campaign to establish 

a tick-free zone in Sinaloa’s northern region, consisting of the municipalities of Ahome, 

Choix, and El Fuerte and extending from the border between Sinaloa and Sonora to the El 

Fuerte River (see Figure 8). This area is currently considered to be in the Eradication 

phase of Mexico’s National Campaign against Boophilus spp. ticks. Surveillance and 

inspection activities are underway with movement restrictions similar to those in place in 

Sonora’s buffer zone. The intent is for surveillance activities to be successfully 

completed and the zone declared Free in 2012 [68, 69]. 

Figure 8. Proposed Rhipicephalus tick-free zone in northern Sinaloa (northern border of 

Sinaloa to the blue line, which represents the El Fuerte River).

Source: [68]

Discussion

The desert habitat throughout most of Sonora and northern Mexican States is inhospitable 

to the survival and maintenance of Rhipicephalus spp. ticks, limiting their potential for 

infestation and subsequent distribution in these areas. 

The area of Sonora at greatest risk for tick incursions is along its southern boundary,

which adjoins the State of Sinaloa, much of which is infested with Rhipicephalus spp. 

ticks. Additional protective measures implemented along the southern region of Sonora 

(i.e., within the buffer zone), such as tick inspection and dipping requirements prior to 

movement, supplemental tick surveillance of livestock, and routine administration of tick 

treatments on high risk premises adjoining the border with Sinaloa, appear to have 

limited the spread of Rhipicephalus spp. ticks within this region and prevented expansion 

of outbreaks out of the buffer zone. However, recent detections of infested cattle close to 

the Sinaloan border indicate that the risk of infestation persists along this border. The 
31

achievement of tick-free status of the northern portion of Sinaloa, if it occurs, could 

mitigate this risk. 

4. Extent of active tick control program 

The State of Sonora, in combination with SAGARPA and the Cattlemen’s Union, 

conducts many different activities which, even if not specifically developed for the 

purpose of detecting, controlling, and preventing the introduction of ticks, serve the tick 

control program in some capacity. 

Livestock inspection and dipping stations

The cornerstone of Sonora’s tick program is the network of official tick inspection and 

dipping stations located throughout the State. Sonora employs the use of a number of 

different types of stations at targeted locations, each of which meets different needs with 

respect to movement controls and tick inspection and dipping (see Section 7 for 

additional information). 

The type and location of the various inspection and dipping stations are represented in 

Figure 8, below. They include the seven Estaciones Cuarentenarias, or quarantine 

stations, which contain livestock corrals and facilities for scratch inspection and tick 

treatment (including dipping vats) for livestock. Three of the quarantine stations are 

located at Sonora’s borders and are used to inspect and treat incoming livestock while 

four are located internally and are used to inspect and treat livestock moving within 

Sonora. The baňos de linea, or line dipping vats, which consist of seven additional 

inspection and dipping stations located in Sonora’s buffer zone, provide additional 

inspection and treatment facilities for livestock that are transiting or moving out of the 

buffer zone. The cordon zoosanitario, or zoosanitary cord, is made up of smaller 

livestock inspection stations located along the mountainous border with Chihuahua; the 

Centros de inspection are large livestock inspection stations located throughout the State; 

the casetas are large agricultural inspection stations that handle both plant and animal 

inspections; the localidads are smaller agricultural inspection stations that may or may 

not provide livestock inspection but will inspect their documentation; and the puntos are 

truck inspection points that inspect paperwork [20, 60]. 

Figure 9. Agricultural Inspection Stations, Sonora, Mexico.
32

Source: [63]

The primary barriers to the entry of tick-infested livestock into Sonora are the quarantine 

stations, particularly those located along Sonora’s border. The three major quarantine 

stations located along the main routes of entry from surrounding Mexican States are: 

Puerto San Luis, at the northern entry road from Chihuahua into Sonora; Maycoba, along 

the central access road from Chihuahua; and Estación Don, at the point of entry from 

Sinaloa to Sonora. One additional point of entry, San Luis Rio Colorado, is located along 

the narrow juncture between Baja California and Sonora; however, this station only 

includes a documentation check and only allows entry of livestock that are transiting 

Sonora. 

These stations provide assurance that all livestock entering the State are evaluated for 

ticks and other animal health conditions. The first step is a review of the accompanying 

documentation for completeness and accuracy with respect to the number, type, and 

identification of animals in the shipment and verification that the numbers on any official 

vehicle seals match those on the documentation. Inspectors also verify that required 

health documents are present according to the animal health status of the region of origin 
33

of the livestock. Livestock also receive a scratch inspection for ticks, and treatment for 

ticks, usually in the form of dipping in an acaricidal solution. If any ticks are found on 

any of the incoming animals, the entire lot is either returned to its place of origin or 

quarantined at the inspection facility and re-inspected and re-treated for ticks until the lot 

has been found free of ticks [20, 54]. 

There are four additional quarantine stations located within Sonora along major roads 

within the State. All livestock entering Sonora (with the exception of Baja California) or 

moving from higher tick risk areas within Sonora are required to stop at one of the 

quarantine stations for documentation verification, scratch inspection, and treatment as 

described above [20, 70]. 

The line dipping vats provide additional opportunities for tick inspection and dipping for 

livestock transiting or moving out of the buffer zone (in line with movement 

requirements for livestock originating from or transiting this area) [20, 60]. 

The other types of inspection stations are overseen by State, Federal, or local authorities 

and perform documentation checks on shipments of livestock moving within Sonora. 

These stations are located throughout Sonora. The inspectors at all of the stations listed, 

even those that are not intended to provide livestock inspection, evaluate the 

documentation of all livestock shipments in order to verify that they are accompanied by 

the appropriate paperwork, including documents verifying current tick inspections and 

treatment when required by Federal and State regulations [20, 60]. 

Operations and facilities at the quarantine stations and line dipping vats will be discussed 

in greater detail below in section 7.

Tick surveillance

Sonora also has a robust surveillance network that has been shown to provide rapid 

identification of ticks found on livestock within the State (which has only occurred within 

the buffer zone to date). The inspection and dipping stations located throughout Sonora 

are part of this network, in that official inspections are provided routinely to animals 

engaged in movement throughout Sonora. The system of movement checks and penalties 

makes it very difficult for livestock producers to evade these inspection points.

In addition, enhanced surveillance activities are conducted by State officials in Sonora’s 

buffer zone, due to the increased risk of ticks or infested livestock moving from the tick 

eradication area in Sinaloa and southwestern Chihuahua into Sonora. Measures 

employed here include campaigns conducted in the high risk area of the buffer zone (i.e., 

premises located along the border with Sinaloa), which involve inspection and treatment 

of livestock in these areas every 4-6 months. Portable chutes are brought onto the 

properties if necessary in order to conduct scratch inspections and treatments of all 

livestock on the properties (either spray treatment with acaricide or ivermectin injection 

for cattle that will be going to pasture for several months and won’t be accessible). The 

brigades operate in addition to the regular livestock inspectors located in the buffer zone, 
34

consisting of 3 teams of 2 individuals each. They also work with personnel from the 

government of Sinaloa when working areas on the border between the two States [54]. 

Sonoran officials also collect ticks as part of a National tick survey orchestrated by 

SAGARPA. The survey is designed to detect ticks if present in 1% of the cattle herds in 

Sonora with a confidence of 99% (within herd confidence is 95% confidence of detection 

at 10% prevalence). This study is conducted across Mexico to determine the national 

prevalence data for tick infestations. This sampling was instrumental in identifying the 

four infested premises in the buffer zone during the 2009 cycle. The 2010 tick survey, 

which tested over 14,000 head of cattle on 481 premises throughout Sonora, and the 2011 

survey, which has tested 151 premises as of September 2011, have not detected any 

Rhipicephalus spp. ticks in any area of Sonora [62, 71]. Additional information is 

provided in section 9, below.

Tick control measures

When ticks are identified on Sonoran livestock, measures are immediately taken to 

identify the ticks, determine their resistance profile, provide treatment and inspection of

the animals until the ticks have been eliminated, destroy any contact materials, such as 

food and bedding, and restrict movement of the animals until the infestation has been 

cleared. When ticks are identified in animals that originate from Sonora, whether at an

inspection station or on the farm during surveillance activities, the entire farm of origin of 

the animal(s) is immediately placed under quarantine by the local livestock inspector (the 

quarantine is based on both Federal and State authority) and Sonora and SAGARPA 

officials are notified. All of the animals on the farm are inspected for ticks. Any ticks 

found are submitted to CENAPA for identification and determination of resistance, and 

all livestock on the farm are treated for ticks. Animals are re-inspected and re-treated 

every 60 days until the conclusion of the quarantine period [10, 54]. 

An epidemiologic investigation is also conducted by Sonoran livestock officials at this 

time. Any farms that have received or sent livestock to any affected premises are placed 

under quarantine until an investigation into their herd or flock can be conducted. If no 

ticks are found on any of the animals the quarantine is lifted and animals are free to move

[54]. 

All animals on premises where ticks have been detected (or livestock with ticks have 

originated) are maintained under quarantine by the local livestock inspector for an 

extended surveillance period which must encompass at least one inspection during 

successive summers and one inspection during the intervening winter season, for a 

duration of approximately one and one half years (once the infestation has been 

completely cleared and assuming no additional ticks are found on any of the animals). 

All premises within 10 km of the affected herd are considered within the perifocal zone 

and are also placed under movement restrictions. During the quarantine period, livestock

on affected premises are only allowed to leave after first getting a permit from State 

authorities, and then are subject to an on-farm inspection; if not ticks are found they are 

then allowed to go to a designated dipping vat facility for treatment. Livestock on 

perifocal premises (within 10km of the affected premises) must go immediately to a 
35

dipping facility and receive a dipping certificate before being allowed to move further

[54, 65].

In addition, all premises within a 10 km radius of the infested farm are investigated and 

all livestock on these farms are inspected for ticks by the livestock inspector (and backup 

or supervisory inspector if necessary). If any ticks are found they are treated as above 

and the 10 km radius is expanded to address any additional premises located near the new 

premises. Animals located within the 10 km radius of infested premises are also under 

limited movement restrictions for the duration of the quarantine of the affected/infested 

premises. These animals must receive a tick inspection (and treatment) prior to leaving 

their premises of origin, but once they have received these and no ticks were found, they 

are free to move without further restriction (other than those they would normally be 

subjected to) [54, 62].

If ticks are found on livestock presented to inspection stations an investigation is 

immediately conducted on the premises of origin as described above if the animals 

originate from Sonora. If the animals are from another State, that State will be notified as 

well as SAGARPA and will conduct its own on-farm investigation [20, 54].

In the meantime, the animals present at the inspection station will be treated for ticks, 

placed under quarantine for 72 hours on-site (in the in-take or “dirty” corrals), reinspected and, if no ticks are found, treated again and then released to their original 

destination. If ticks are found upon re-inspection, then the cycle is repeated until the 

animals have been found to be clean of ticks. Different acaricides are used depending on 

the number of treatments required and the resistance profile of the ticks once those results 

have been received (for example, coumaphos will be used at 400ppm after the second 

failed inspection and ivermectin may also be used). Additionally, any bedding or feed 

that arrived on the transport vehicle with the load is disinfected and incinerated on-site 

and the vehicle is cleaned and disinfected. Any bedding or feed left over from the 

quarantine corral where infested livestock were maintained is disinfected and incinerated 

in the same manner. The corrals used to house the animals are thoroughly cleaned and 

disinfected after the animals’ departure [20, 54].

All ticks collected by inspectors or other livestock officials, regardless of the site of the 

collection, are submitted to the CENAPA laboratory for identification and resistance 

characterization via courier through the regional supervisor (for livestock inspectors) or 

supervisor (for quarantine and inspection stations) at the State level. These officials also 

notify SAGARPA of the submission. CENAPA reports test results electronically. 

Samples and information on the date of collection, owner of the animals, location of the 

premises or origin, etc. are submitted on controlled forms [20, 54].

It is important that a sufficient number of ticks are collected, since approximately 20 

engorged females are needed for resistance determination to multiple acaricides. This 

has been a problem with regard to some tick collections on livestock presenting at the 

quarantine stations as few ticks have been found, hampering the ability of CENAPA to 

test for resistance. Taxonomic results take approximately 4-5 days to return, including 
36

transport time; however, officials, particularly those at quarantine stations and their

supervisors, are usually able to provide unofficial identification on-site. The 

determination of resistance takes considerably longer, due to the need for ticks to 

complete certain stages of their life cycle [54]. 

Discussion

Sonora’s tick exclusion, detection and control measures have been demonstrably 

effective. Officials are knowledgeable and effectively track movement of livestock, tying 

it together with all necessary tick inspection and treatment documentation according to 

the location of the point of origin of the livestock. Detection of incursions appears to be 

done in a timely manner and control measures, including quarantine, further inspections, 

investigations, and treatment have been effective.

The interrelated measure described above and throughout this document indicate the 

active role that Sonora, SAGARPA, and the livestock industry play in preventing, 

detecting, and controlling tick incursions in Sonora. 

5. Vaccination status of the region

Sonora does not currently vaccinate against Babesia organisms nor their associated tick 

vectors.

6. Separation from adjacent regions of higher risk

Sonora’s borders include two U.S. States, three Mexican States, and the Gulf of 

California, comprising desert and mountain terrain as well as water. See Figure 10 for a 

map of Sonora and surrounding areas. 

Figure 10. Map of Mexican States surrounding Sonora, Mexico.
37

Source: http://www.map-of-mexico.org/mexico-states.gif

Much of the land area surrounding Sonora is considered free of Rhipicephalus spp. ticks, 

by either Mexico or the United States. Sonora’s northern border, which adjoins the U.S. 

States of Arizona and New Mexico, is relatively flat and free of geographic barriers. It 

consists mostly of desert terrain and is not conducive to the survival and propagation of 

Rhipicephalus spp. ticks. Additionally, both U.S. States are free of these ticks. 

Baja California shares a small land border with Sonora’s northwestern tip. The only 

entry point between Sonora and Baja California is located in San Luis Rio Colorado. The

Colorado River and the Altar Desert form most of the border between the two States, 

creating an area that is inhospitable to Rhipicephalus spp. ticks. It is considered free of 

Rhipicephalus spp. ticks by Mexico and is currently under evaluation by APHIS. The 

remainder of Sonora’s western border consists of the Gulf of California.

Along the eastern border of Sonora lies the Western Sierra Madre mountain range, which 

provides a physical barrier between Sonora and Chihuahua, particularly along the 

northern portion of this border. Because of the difficult nature of the terrain in this 

region, there are only two major access roads with entry points between the States of 

Chihuahua and Sonora. Although Chihuahua has been declared tick-free by the Mexican 

government, it has not yet been evaluated by APHIS and therefore is not currently 

recognized as free by the United States. 

Sonora borders Sinaloa to the south, along a relatively narrow strip of land. An 

inspection point is located along the main route of entry, at Estación Don, and although 

there are other points of entry from Sinaloa, these roads are generally impassable to 

shipments of livestock. However, individual livestock may be able to pass back and forth 

between premises adjacent to or straddling the border between the two States. The State 

of Sinaloa is not considered free of Rhipicephalus spp. tick at this time.

There is a potential for infested wildlife to enter Sonora from the surrounding Mexican 

States. Unlike Sinaloa, Baja California and the majority of Chihuahua, including the part 

which adjoins Sonora, have been declared free of Rhipicephalus spp. ticks by the 

Mexican government and are not a likely route for entry of infested wildlife. The border 

with Sinaloa, which is the only adjoining area to Sonora likely to harbor Rhipicephalus

spp. ticks, is relatively short, providing minimal opportunity for entry of infested wildlife. 

Additionally, supplemental surveillance and routine treatment measures against ticks are 

in place for livestock located in the buffer zone in southern Sonora, providing enhanced 

protection of livestock along this border, in order to combat a possible incursion of 

Rhipicephalus spp. ticks from infested wildlife into the livestock population.

Discussion

Sonora appears to have sufficient physical barriers to effectively isolate the state from 

areas of high risk for Rhipicephalus spp. ticks. It is surrounded along most of its borders 

by natural physical barriers which allow it to funnel traffic coming into Sonora from 

these areas through a small number of paved roads, each of which is equipped with 

inspection and dipping facilities. Areas without physical barriers tend to adjoin tick-free 
38

regions. The southern border of Sonora poses a risk for occasional introduction of ticks 

into Sonora’s buffer zone due to its proximity to a tick-infested region and its relative 

lack of natural borders; however, a number of factors, including enhanced measures for 

the detection and prevention of tick infestations in the region and fencing along the State 

line with Sinaloa, have been successful in mitigating the risk of spread to the northern 

part of Sonora. Additional measures to reduce the risk of future incursions are described 

below. 

7. Movement controls and biosecurity from higher-risk regions

Sonora’s primary barrier to movement of Rhipicephalus spp. ticks from higher-risk 

regions (including from surrounding States as well as Sonora’s buffer zone) is its network 

of tick dipping and inspection stations. These include quarantine stations both at points 

of entry into Sonora as well as internal quarantine stations, their associated inspection 

points, the line dipping vats in Sonora’s buffer zone, and other inspection and document 

check stations, including the sanitary cord inspection stations, agricultural inspection 

stations and local inspection points. Integral to the successful operation of these facilities 

is the State of Sonora’s transit guide, which provides a system for movement tracking and 

verification of livestock combined with mandatory origin identification that allows 

inspection officials to determine compliance with tick treatment and other animal health 

requirements. 

Transit guide system

The cornerstone of Sonora’s livestock movement program is its transit guide (Guías de 

Tránsito) system. No livestock may be moved anywhere in Sonora without a transit 

guide. The transit guide is a controlled form issued by the State of Sonora that tracks the 

origin and movement of livestock. It also captures information on the number and type 

of animals being moved, dates of movement, premises of origin and destination, and herd 

identification number and brands [54, 56, 63]. 

Transit guides are issued by livestock inspectors or quarantine station officials. Before 

issuing a transit guide to animals leaving their premises, a livestock inspector checks the 

health of the animals being moved through a thorough inspection, verifies their 

ownership, and makes sure that the animals have been properly identified, using either 

the Sonora herd identification system or the National voluntary tagging system, both of 

which include a code that lists the animals’ herd and municipality of origin. Transit 

guides include an expiration date that is based on the expected amount of time necessary 

to complete the movement. Most transit guides expire after 24 hours, although some may 

be issued for 48 hours. Once animals have reached the official station, a new transit 

guide may be issued for any destination within Sonora once the animals and/or their 

documents have passed inspection and received any necessary treatment. Under Sonora’s 

Livestock Law, individuals who violate the terms of the transit guide or attempt to travel 

without one are subject to legal sanctions, including fines or even forfeiture of the 

livestock involved in the illegal movement [54, 56, 63]. 
39

Once livestock reach the destination stated on the transit guide the transit guide is 

cancelled by livestock officials (either quarantine inspectors or local livestock 

inspectors). In the case of animals that are en route to their final destination a new transit 

guide will be issued. Some of the officials at inspection stations are able to access the 

electronic database for transit guides and can enter and cancel transit guides in this 

system directly, but most local livestock officials only handle paper forms. Copies of 

transit guides are sent to the State offices where the information is entered into the 

electronic movement database (if it has not already been entered) and officials there 

verify that livestock reached their destinations within the allotted amount of time [54]. 

During the 2011 site visit, quarantine officials stated that this activity was currently 

conducted by hand, but that they were nearing completion of an automated system. Also, 

in many cases the livestock official will call an inspection station to alert them to an 

incoming load or when the inspection stations have access to the electronic movement 

database, they will know immediately if a livestock load fails to show up. If this happens 

the regional supervisors at the origin of the livestock will be contacted and will perform 

an investigation. If necessary, the police will be notified to assist with locating the 

livestock. This has been a very rare occurrence in Sonora [54]. 

Movement of ruminant livestock and horses into Sonora 

The importation of livestock into the State of Sonora is regulated by the Federal Law of 

Animal Health, the Livestock Law of the State Government of Sonora, and the NOM019-ZOO-1994 (National Campaign against the tick Boophilus spp.). All livestock 

entering Sonora, either as a final destination or for transit purposes, must first acquire a 

permit from the State of Sonora DGSG. The requirements for receipt of a permit depend 

on the disease and ectoparasite status of the State or country of origin of the livestock

[54, 56].

Livestock entering Sonora from neighboring Mexican States must pass through one of the

official quarantine stations located along the main routes of entry into Sonora. These 

quarantine stations are situated on paved highways entering Sonora and their facilities 

include livestock holding pens, a scratching chute for tick inspections, a tick dipping vat, 

and spray equipment for horses and small ruminants. They include Estación Don, on the 

southern entry route into Sonora from Sinaloa, Puerto San Luis, on Sonora’s western 

edge along the northern road from Chihuahua, and Maycoba, also on Sonora’s western 

edge, but located midway along Chihuahua’s border. The San Luis Rio Colorado station,

on the border between Sonora and Baja California, does not provide scratch inspection 

and dipping functions since livestock from Baja California are currently only allowed to 

transit Sonora and thus are only required to undergo a documentation check since they 

will not be unloaded within Sonora [20, 63, 72].

All livestock entering Sonora are required to be accompanied by an entry permit, a transit 

guide, a zoosanitary certificate, a herd of origin certificate, and a tick dipping certificate. 

The zoosanitary certificate is a general livestock health certificate required by 

SAGARPA for movement between Mexican States and issued by an official or accredited 

veterinarian. It includes information on the number, type, origin and destination of 
40

animals in a shipment. All vehicles transporting livestock into Sonora must be sealed at 

the point of origin, with the quarantine station at the entry point of Sonora responsible for 

verifying that seals are intact and that the seal number matches that provided on the

zoosanitary certificate and transit guide. Livestock that are entering Sonora from other 

countries must also be accompanied by a zoosanitary requirements sheet, which spells 

out the requirements for entry of livestock into Mexico and is verified by SAGARPA 

officials at the internal verification points (or PVIs) [3, 20, 54, 56, 60]. 

Each entry quarantine station is associated with a PVI. Whereas the quarantine stations 

are run by the State of Sonora, the PVIs are operated by SAGARPA; therefore the focus 

of their inspection is primarily on Federal entry requirements. The PVI addresses both 

animal and plant health concerns whereas the quarantine station addresses animal health. 

The PVI may be located before the quarantine station, as is the case with Estación Don, 

or after the quarantine station, as with Puerto San Luis and Maycoba. Personnel at the 

PVI focus their evaluation on the documentation accompanying the livestock load. They 

check to make sure the appropriate documents have been acquired, that the information 

on the documents matches the animals in the load (number and type of animals, 

identification tags and brands), and that the seals and vehicle licenses also match [54]. 

In addition to the documentation check at the PVI, livestock entering Sonora must also 

pass through the quarantine station. The quarantine station is under the control of the 

State authorities and staffed by personnel employed by the State of Sonora. Its personnel 

provide inspection and dipping for ticks, as well as a second review of the accompanying 

documentation, with a focus on State requirements. Livestock that have passed 

documentation checks are unloaded into the “dirty” corrals, which are used to hold 

animals that have not yet been inspected and dipped for ticks, then moved to chutes for 

individual inspection. Most of the chutes used at Sonora’s entry quarantine stations are 

narrow enough to maintain cattle in single-file formation, use grates for flooring to allow 

feces and other organic material to pass through (reducing contamination of the dipping

vat), and include slats that open up to allow for scratch inspection of the ventral area of 

livestock for ticks. An exception to this was noted at Estación Don during the 2011 site 

visit. Slats were observed to be used as flooring for the chutes, rather than grates, which 

are generally less effective at maintaining sanitation, and the chutes were not as narrow, 

allowing cattle to bunch up and making inspection more difficult [54]. 

Once the tick inspection has been completed, livestock proceed through the dipping vat

where quarantine station personnel provide assistance in ensuring that all cattle are 

adequately covered, including their heads. Cattle then enter a drying pen where they stay 

for 5-10 minutes to allow excess acaricide to run off and be recycled back into the tank,

then proceed to the “clean” corrals where they can be re-loaded onto vehicles and 

continue their journey. (Horses and small ruminants are treated using spray equipment.) 

Provided no ticks were found during the physical inspection, and all paperwork was 

found to be accurate and complete, quarantine station personnel will issue a dipping 

certificate and transit guide for the animals’ destination (or port of exit in Sonora if 

transiting the State). If the animals have been traveling for long periods, then they may 

be allowed to rest for a few hours in the clean pens before being re-loaded; however, if 
41

the livestock are from another state they will not be allowed to use their own feed and 

must purchase local feed from the station [20, 54].

The number of cattle imported into Sonora from other Mexican States ranged from 

162,000 to 277,000 head per year from 2008 to 2010. The vast majority (between 92 and 

96%) of these animals were transiting the State, destined for the Mexicali Valley feedlots 

in Baja California. Cattle at these feedlots all receive the “CN” brand and are intended 

for domestic consumption (within Mexico) only. The intended uses for the relatively 

small number of cattle destined to remain in Sonora include feeding, breeding, and sport, 

for the most part [54, 61]. 

Imports of livestock from outside of Mexico require a permit from SAGARPA prior to 

entering the country and issuance of a zoosanitary requirements sheet. The specific 

requirements are based on the animal disease and ectoparasite status of the exporting 

country [20, 54]. 

The vast majority of livestock imported into Mexico from other countries originate from

within the United States. Cattle imports from the United States averaged 20,000 head per 

year during 2009 and 2010, and imports from Canada made up the remainder of imports, 

averaging approximately 1,500 head per year. Sheep and goat imports all originated in 

the United States for 2009 and 2010. Equine imports ranged from 80,000 to over 

100,000 head during this time period, with approximately 99% originating from the 

United States [73].

To date, no ticks have ever been found at inspection stations on animals originating from 

Sonora, however, there have been tick identifications on animals entering Sonora from 

other States, most notably at Estación Don, at the southern end of the State in the buffer 

zone [54].

Livestock transiting Sonora from Baja California

Livestock transiting Sonora from Baja California to other Mexican States (either for

residence or eventual export to the United States) via the entry point at San Luis Rio 

Colorado are not off-loaded for tick inspection and treatment. A document check is 

completed, seals and license plates are checked, and the animals are issued a transit guide

to the port of export. The rationale for this process is to reduce the risk of introducing 

acaricide resistant ticks into Sonora. Off-loading the animals could result in dropping

ticks in the area of the quarantine station if ticks are present, with the possible infestation 

of subsequent animals passing through or held at the quarantine station. However, the 

risk of introducing infested livestock via this route is significantly mitigated by Baja 

California’s Rhipicephalus spp. tick-free status as declared by Mexico [74].

Movement of livestock from the buffer zone to the northern part of Sonora

The area of southern Sonora that adjoins Sinaloa and the southwestern corner of 

Chihuahua is referred to as the buffer zone for Rhipicephalus spp. ticks. It is comprised 

of portions of the municipalities of Álamos, Huatabampo, Navojoa, and Etchojoa. Due to 

its proximity to areas considered infested with Rhipicephalus spp. ticks and the lack of 
42

significant geographical barriers between infested and free zones, the buffer zone is 

considered at risk for re-infestation with Rhipicephalus spp. ticks (and incursions have 

been detected in recent years). Therefore, enhanced detection, prevention, and control 

measures are employed in the buffer zone [20, 53, 72]. 

Livestock originating from premises in the buffer zone that are planning to move into the 

northern tick-free area of Sonora are required to stop at the Bahuises quarantine facility

which is located at the northern border of the buffer zone, where their documents are 

checked, and the animals are inspected and dipped before being moved out of the buffer 

zone. No ticks have been found in livestock presented at the Bahuises facility [53]. 

There are seven line dipping vats, or dipping vat facilities, located along Sonora’s 

southern border. These provide an additional layer of surveillance and tick treatment for 

livestock within or moving through the buffer zone. The line dipping vats, located along 

the major access roads, have facilities for inspecting and dipping cattle (or spray treating 

other livestock). Transit guides may be issued from line dip bath personnel and local 

livestock inspectors in the buffer zone for movement to the nearest quarantine station

(Bahuises) only. See Figure 11 for a diagram of the line dipping vats and quarantine 

stations used by livestock departing the buffer zone. The seven line dip bath facilities are 

represented by yellow text, and include: San Bernardo, Las Chinacas, El Sabino, 

Masiaca, Palos Chinos, Maquipo, and Tapizuelas. The green text represents the 

quarantine stations: internal stations Guasimas and Bahuises on the road leading out of 

the buffer zone; and import station Estación Don with its associated PVI (in red) at the 

road leading into Sonora from Sinaloa [20, 54, 72]. 

Figure 11. Tick inspection and dipping facilities in Sonora’s buffer zone.

Source: [62]
43

Livestock residing in the area of the buffer zone adjoining Sinaloa and Chihuahua must 

go to a line dip bath (which are concentrated in these areas) before leaving the buffer 

zone. There they will be inspected and treated for ticks and a transit guide will be issued 

by the dipping vat inspector with the Bahuises quarantine station as the destination. At 

the Bahuises quarantine station the livestock will be inspected and dipped again before 

being allowed to proceed to the northern part of Sonora (or Guasimas if traveling at 

night). Livestock from other areas within the buffer zone will be issued a transit guide 

directly to the Bahuises quarantine station by the livestock inspector for their area. These 

livestock will receive a tick inspection and treatment at the quarantine station and the 

inspector can then issue a transit guide to their final destination. Any livestock shipments 

that try to avoid the Bahuises station (which only operates during one 8 hour shift each 

day) will be intercepted at the Guasimas inspection point, which is farther north along the 

highway and operates 24 hours a day [54].

Therefore all livestock moving into northern Sonora from the buffer zone will receive at 

least one inspection and tick treatment at a state-run quarantine station facility, and 

livestock originating from the higher risk area of the buffer zone (i.e. areas near tickinfested borders) will receive an additional inspection and treatment at a locally-run line 

dip bath. Approximately 30% of cattle in the buffer zone reside in the higher risk area 

and are subject to two tick inspections and two treatments before moving out of the 

buffer zone (cattle on these ranches also receive ivermectin injections two to three times 

per year) [54]. 

When ticks are found on livestock presented at any of the dipping stations, the tick(s) and 

information about the circumstances of the collection and origin of the livestock are 

provided to the supervisor (there is one supervisor for the quarantine entry stations, one 

for the internal quarantine stations, and another for the line dipping vats; all are employed 

by the State of Sonora). The supervisor sends the ticks and submission form to the 

CENAPA laboratory for identification and resistance analysis via courier and results are 

sent back to the supervisor electronically and the supervisor notifies his chain of 

command in Sonora, as well as SAGARPA and the dipping station inspector. In the 

meantime the infested shipment is quarantined, treated, and re-inspected as described in 

Section 4 [20, 54].

Movement of livestock entirely within the buffer zone 

Movement of animals entirely within the buffer zone requires a transit guide prior to 

movement. Tick dipping is not required if no ticks are identified during the inspection 

process and if the animal is not moving outside of the buffer zone [71, 74, 75]. 

However, cattle from high risk areas within the buffer zone, particularly premises located 

along the border with Sinaloa or Chihuahua, are required to receive a tick inspection and 

dipping certificate before the livestock inspector will issue a transit guide for movement. 

Livestock owners may acquire advanced approval by telephone from the livestock 

inspector to move their livestock to the nearest line dip bath in order to be dipped [71]. 
44

Movement of livestock exclusively within the northern tick-free area of Sonora

Movement of ruminant livestock and horses within the tick-free region of Sonora requires 

that a transit guide be issued by a livestock inspector prior to the animals leaving the farm 

of origin. Although a thorough scratch inspection for ticks is not required for this type of 

movement, a thorough inspection of general health is required, which would potentially 

detect a tick infestation, if present. A dipping certificate is not needed as long as the 

animals do not transit the buffer zone [20].

Dipping vat management

An integral component of Sonora’s tick control program, with respect to prevention of 

entry as well as enhanced detection and control of spread, is its system of dipping stations 

located throughout the State. Tick dipping is generally accomplished by immersing cattle 

in a vat or bath filled with acaricide solution. The vat itself is often located below ground 

level, and cattle walk down a ramp until their entire body is submerged in the solution. 

Handlers make sure that each animal’s head also becomes immersed. Horses and small 

ruminants are treated using spray equipment. Although there are different types of 

stations, each of which meets different needs, the dipping facilities themselves are all

managed in a similar manner. Specific guidance on procedures at quarantine stations and 

line dipping vats, including acaricidal solution maintenance and sample collection, tick 

collection, record keeping, and document review, are contained in Sonora’s operational 

manual for quarantine stations and line dipping vats.

Dipping vat facilities and operations

There are different types of stations used in the inspection and treatment of livestock for 

ticks as they move into and throughout Sonora. This section will focus only on those 

facilities that contain dipping vats, including the quarantine stations of entry into Sonora, 

the internal quarantine stations, and the line dipping vats.

The official quarantine stations, both for entry and internal movement, operate under the 

oversight of the State of Sonora (although the PVIs associated with entry quarantine 

stations are under Federal control). The inspectors who work at these stations are 

employed by the State of Sonora. All livestock entering Sonora, or moving north into the 

tick-free area of Sonora must pass through one of these quarantine stations [20, 70].

The line dipping vats, located in Sonora’s buffer zone, are managed and operated by the 

local AGLs (Local Cattlemen’s Association), with official oversight of day to day 

procedures provided by the Committee, but ultimate supervision and inspection provided 

by the State of Sonora. The local livestock inspector for the livestock zone in which a 

line dip bath is located runs the day to day operations of the line dip bath [20, 54]. 

Physical equipment and infrastructure at dipping vat facilities of the quarantine station 

include an office with internet, fax, and phone. Also evident are maps of Mexican States 

delineated according to tick status, procedural posters and instruction manuals. The 

offices also contain acaricide sample collection jars for submission to the laboratory for 

analysis, tick collection tubes (with 70% alcohol for dead ticks for taxonomy and clean 

tubes for lives ticks for resistance characterization), and pH test strips. Storage facilities 
45

were also viewed, containing pump aerators, acaricide concentrate for recharging and/or 

replacing the dipping vat solution, and sodium hydroxide for pH adjustment. Line dip 

bath inspectors do not maintain an on-site office or storage facility, but keep these items 

in a locked storage facility at home instead and transport them to the dipping vat when 

necessary [54].

All dipping vat stations include the necessary facilities for inspection, dipping, and 

maintenance of the dipping vat solution, although some are better maintained than others. 

All quarantine stations and line dipping vats contained “dirty” corrals for unloading 

uninspected livestock and “clean” corrals for holding the inspected and treated livestock 

prior to re-loading. All of the stations also include chutes for tick inspection of cattle

(other livestock are inspected individually), most of which squeezed the cattle into single 

file and included boards that could stop the cattle for individual inspection, and also 

contained ventral panels that opened for scratch inspection of the flank and brisket area 

and grates on the floor to allow for removal of waste prior to entry of cattle into the 

dipping vat [54]. 

The exception was the quarantine station located at Estación Don as observed during the 

2011 site visit, which allowed for bunching of cattle and did not have grates on the floor. 

It was commented that individual inspection could be conducted in a separate area when 

necessary, and on-site inspection of the facilities by the 2011 site visit team was able to 

determine that scratch inspection was conducted adequately. Other aspects incorporated 

into the design of both the quarantine stations and line dipping vats included covers over 

the dipping vat area to prevent rain and sunlight from reducing the effectiveness of the 

dipping vat solution, cement-floored drip pans for cattle that were just dipped, with drain 

lines equipped with filters to recycle the acaricide solution back into the dipping vat, and 

evaporation pools for discarded acaricide solution resulting from changing out the 

dipping vat [54].

Each dipping station also maintains a log book in which information on each shipment of 

livestock passing through is recorded. The information includes the number and type of 

animals inspected and dipped in each shipment, their identification information (ear tag 

or brand), premises number, the name of the owner, the origin and destination of the 

shipment, and the results of the tick inspection and quarantine information if appropriate. 

This information is kept in the log book at the dipping station and also compiled into a 

bimonthly report, copies of which are sent to State and Livestock Committee offices [54]. 

In addition to the log book, all dipping facilities also maintain a registry that captures 

information about the dipping vat solution and its maintenance, including the number of 

animals dipped, the acaricide concentration, pH, pollution level, and dates of recharging 

and replacement of the acaricide solution. All records are maintained for five years [20, 

54, 56]. 

Operations at facilities that include dipping vats are overseen by a supervisor with the 

DGSG who visits the station once a month (in the case of the quarantine stations) or 

twice a month (for line dipping vats). The supervisor reviews the entries in the dipping
46

vat solution registry book to evaluate whether or not tests are conducted at the 

appropriate frequency, dipping vat solutions have been maintained at adequate 

concentrations, determines whether current procedures are adequate or need to be 

adjusted, and also reviews on-site procedures. Visits can take up to three days for 

quarantine stations. The supervisor consults with the inspector in charge of the station 

and compiles a report with the results of his inspection and any recommendations that 

need to be made. Copies of the report are shared with State and Federal officials and the 

Livestock Association. The supervisor checks on the next visit to make sure that any 

recommended actions were taken in a timely manner and verifies the effectiveness and 

timeliness of the actions based on follow up laboratory results [54].

In addition, an annual audit of dipping station facilities is conducted by State, Federal and 

Committee officials. This review is more intensive than the monthly visit and includes 

evaluation of the facilities, as well as procedures and personnel. It includes inspecting 

the dipping vat roof to verify that the dipping solution is not exposed to direct sun or rain 

water, which can reduce its effectiveness; checking the drying area and the solids 

decanting tank to make sure waste and other organic materials aren’t entering the dipping

vat; checking to make sure the acaricide concentrate is maintained properly; the aerator 

and other equipment is functioning properly; and evaluating day to day procedures [54, 

56]. 

Dipping vat personnel

Inspectors at all quarantine stations are employees of the State of Sonora. These 

personnel generally consist of employees with different backgrounds, some primarily 

plant health and others animal health, but all inspectors receive training in both. 

Inspectors include agricultural techs, agronomists, and veterinarians. All inspectors 

receive training in livestock inspection and handling, tick identification, and the 

administration and management of acaricidal products by technical personnel from the 

DGSG and the laboratories that produce the acaricides. The supervisor or veterinarian at 

the station may always be contacted for assistance if necessary. Personnel at the larger 

quarantine stations with 24 hour a day operations generally work in 8-hour shifts, while 

the smaller stations only operate during daylight hours (although these are associated 

with 24 hour document inspection stations that can hold shipments if inspection is 

required [20, 54].

The livestock inspectors also act as the head inspector for the line dip bath located in their 

livestock zone. They are responsible for coordinating movement of animals within their 

zone through their line dip bath, maintaining records, and keeping the log books. The 

inspector is also responsible for making sure that the dipping vat solution is adequately 

monitored and maintained, which includes providing daily aeration even if no animals are 

scheduled to be dipped [54]. 

During site visits, inspectors and their supervisors were found to possess overall 

knowledge of the eradication program and its requirements, as well as a high degree of 

professionalism. In addition, the number of personnel providing inspection services and 

staffing of the dipping and quarantine stations was found to be sufficient during all three 
47

site visits. While some documentation reflecting monthly reports was found to be less 

frequent than stated, the reports that were viewed were complete, and appropriate 

measures were taken as indicated in the reports [54, 63, 72]. 

Acaricide management

The three dipping vats at the quarantine stations of entry into Sonora use amitraz6 at a 

concentration of 400 ppm, which is twice the strength recommended on the product label. 

The CENAPA laboratory determined this concentration to be effective against amidineresistant ticks in other parts of Mexico. The four internal quarantine stations and line 

dipping vats use organophosphates in their dipping vats. Organophosphate acaricide 

solution at a concentration of 200 ppm is also used in spray equipment used to treat 

horses and small ruminants [54, 60].

All acaricides used in Mexico are registered by SAGARPA and have passed biological 

testing performed at CENAPA demonstrating a minimum efficacy of 98% prevention of 

successful feeding, egg laying, and larval emergence according to the Mexican Official 

Standard NOM-006-ZOO-1994 [60].

Although the type and purpose of many of Sonora’s tick dipping stations vary, handling 

and control procedures for the dipping solutions are the same, with a number of different 

methods used to monitor their effectiveness. These procedures are reviewed on a 

monthly or bi-monthly basis by the dipping vat supervisors. The State Supervisor of the 

SFG is ultimately responsible for ensuring that these activities are carried out in an 

appropriate and timely manner [60]

Acaricide solution can lose its effectiveness if exposed to excessive organic matter or

other sediment. Sonora uses pump filtration systems in its dipping vats to provide 

continual removal of mud, hair, and other organic material that can end up in the solution. 

The pump is set up to filter the entire content of the dipping vat every 1000 animals. In 

addition, the contamination level of the tick bath solution is checked every 250 animals 

or every month, whichever is more frequent. This is done by measuring the sediment 

level in a one-liter test tube filled with the used acaricide solution. When the level of 

sediment reaches 15% the entire tank must be changed. Records reviewed at the 2011 

site visit showed that pollution levels rarely exceeded 10% before the dipping vat 

solution was replaced completely [54, 56, 60]. 

The lack of consistent and effective mixing, or agitation of the dipping vat solution 

during previous site visits was found to result in inadequate suspension of the acaricidal 

chemical in the dipping vat solution and lowered concentration levels. As a result, 

APHIS recommended that all dip vats acquire pump aerators and aerate the dipping vat 

solution for 40-50 minutes at the beginning of every day, whether or not animals were 

scheduled to be dipped that day. The 2011 APHIS site review team was able to verify 

that all dipping stations had pump aerators equipped with T-bar attachments to the hoses 

 6 Amitraz is an amidine antiparasitic agent that is available in different formulations and is effective against 

cattle fever ticks.
48

for better distribution and the inspectors demonstrated that the solution was aerated every 

day, beginning at the start of the day [54, 63]. 

Maintenance of proper pH levels is important to the maintenance of the acaricide 

concentration level and, in the case of organophosphate acaricides, to prevent the buildup 

of toxic byproducts of decomposition of the acaricide. Label recommendations advise 

that the pH of the acaricide solution be evaluated daily for the amidines, and it appeared 

that this was done regularly by dipping vat employees. For amitraz, the pH should be 12 

or higher (this is corrected by adding calcium hydroxide or lime to the bath if the pH is 

too low), and for organophosphates the pH should be as close 7 as possible. The pH 

levels are adjusted when indicated by adding calcium hydroxide (to increase the pH when 

amidines acaricide is being used) or acidifiers as necessary. The pH levels of acaricidal 

solution are evaluated by CENAPA along with pollution levels when the solution is 

submitted for concentration analysis, but the staff at the dipping stations keep pH strips 

on hand and can monitor and record results in real time [54, 76]. 

The APHIS team recommended that Sonora begin evaluating the pH of their 

organophosphate dipping vat solution on a daily basis and maintaining the levels closer to 

5.5 using triple phosphate to decrease the pH when necessary. Recent research at 

APHIS’ Agricultural Research Station revealed that maintaining the coumaphos at this 

level helped maintain the concentration of the acaricidal solution and eliminated or 

reduced the amount of toxic byproducts. Sonoran officials requested that APHIS share 

the protocol they had developed based on this information so they could implement it as 

soon as possible (they were currently following the label recommendations for 

coumaphos, which advised a neutral pH) [54, 56, 60].

Each dipping station has instructions on how to recharge the dipping vat contents with 

fresh acaricidal concentrate and when this is necessary in order to maintain an 

appropriate concentration. Each dipping vat contains an adjacent recharging container 

that contains measurements to assist with adding new acaricidal solution to the dipping

vat. The specific amounts of concentrate, water, and calcium hydroxide are provided in 

Sonora’s quarantine station operating procedures manual in a formula for a standard 

recharging. Additionally, CENAPA will provide specific recommendations and amounts 

for recharging in the event that the concentration of acaricidal solution is low and 

additional concentrate needs to be added. Re-loading of the acaricide in the dipping 

solution is scheduled to occur after 250 animals have been dipped (for amitraz) or when

the solution level in the dipping vat tank has declined by 500 liters (for both amitraz and 

coumaphos). In addition, a sample of dipping vat solution is collected in a clean brown 

glass collection vial and sent to CENAPA for a concentration analysis every 1000 head 

(or every 3 months, whichever is sooner) [54, 56, 76]. 

The dipping vat solution must be completely replaced every 5,500 head or when the 

pollution level reaches 15% (whichever comes first) or once per year in the event that 

fewer than 5,500 cattle are dipped in a year’s time (as is the case at all of the line dipping 

vats). The discarded solution is emptied into an evaporation tank which allows the 

unused acaricidal solution to volatize safely [54, 76].
49

The on-site registries for dipping vat solution management viewed during the 2011 site 

visit demonstrated that inspectors were conducting the above activities as prescribed, and 

were able to maintain acaricide concentrations within the effective zone. Amitraz 

concentrations at the external quarantine stations were usually above 400 ppm and rarely 

dipped below 300 ppm (which is well above the effective concentration according to the 

label). Similarly, coumaphos levels at the line dipping vats were rarely found to be 

below 200 ppm. Pollution levels and pH tests were conducted at the required frequency

and all were within target ranges. Similarly, acaricide concentration was checked, 

recharges conducted, and dipping vat contents replaced according to the protocol. The 

documentation was complete and matched what was provided in the animal movement 

log books, the supervisors’ reports, the laboratory submission and report forms, and any 

recommended adjustments to dipping vat procedures or contents were quickly acted upon 

by the dipping vat inspectors [54]. 

During the 2011 site visit it was determined that the turnaround time for receipt of 

acaricidal solution analysis results from the CENAPA laboratory generally took three 

weeks, and sometimes longer than four weeks. Although on-site inspectors and 

supervisors made the necessary corrections to the solutions based on laboratory results, 

the delay in receipt of laboratory results meant that the dipping vat solution often had 

already received a number of recharges or, in some cases, complete replacement by the 

time the findings and associated recommendations were received, rendering the 

recommendations practically useless [54].

The dipping vats used at the quarantine stations and line dipping vats are designed for use 

by cattle and are not appropriate for horses and small ruminants. These animals are 

therefore treated using spray equipment rather than the dipping vats. Organophosphates 

are used in the spray equipment and the equipment is cleaned and flushed with clean 

water after each use. Any unused solution is discarded after use [56, 60].

When treating an animal with spray equipment, one liter of solution per 100 kg of weight 

is prepared and applied so that each animal becomes thoroughly wet. The solution is

applied to the animal’s entire body, particularly difficult to reach areas such as the base of 

the tail, the ears, the groin, and inside the legs. As with the dipping vats, dates of 

treatment, number of animals treated, and the name and amount of the product used are 

recorded in the register [56]. 

Controls on hay and other forages entering Sonora

Because hay and other forages can harbor ticks and other pests, the government of 

Sonora regulates the importation of these products. Most livestock in Sonora are kept on 

pasture; therefore there is little demand for imported hay and forages for livestock

feeding. Forage materials that are used for Sonoran livestock generally originate from 

within the State and seeds used to sow these crops are acquired primarily from the United 

States and must comply with phytosanitary (plant health) requirements [56]. 
50

When importation of forage is necessary, requirements contained in the Official Mexican 

Standard NOM-044-FITO-1995, which spells out the phytosanitary requirements and 

specifications for the import of nuts, vegetable products, and vegetable byproducts, must 

be followed. Additionally, in 2000, USDA APHIS performed a risk assessment and site 

visit for the importation of hay from the Mexicali region of Baja California to the United 

States. The evaluation determined that there was no risk of importing tick-infested Sudan 

hay (the major crop in this region), but that opportunities existed for contact of cattle with 

some other forage crops. Therefore, hay from this area was allowed entry into the United 

States provided it was accompanied by certification stating that no potential tick-infested 

animals were allowed access to the hay pasture during production or harvesting [77, 78].

Movement of infested wildlife into Sonora

The most likely avenue for movement of Rhipicephalus-infested wildlife into Sonora is 

via the southern border of Sonora due to that area’s proximity to tick-infested regions of 

Mexico. Although cattle are the preferred host for Rhipicephalus ticks, other hooved 

animals, including white-tailed deer have also been found to harbor these ticks. While 

white-tailed deer have been demonstrated to maintain Rhipicephalus tick populations in 

previously infested cattle ranges, other wildlife species have not been implicated in the 

maintenance of these ticks to date [79, 80].

If infested wildlife were to become established in Sonora it is likely that the ticks would 

also be present on cattle in the region. Because of the intensive surveillance and preemptive treatment measures performed by local and special livestock inspectors and at 

dipping vats and quarantine stations in the southern portion of Sonora (the buffer zone), it 

is likely that infestation of cattle or other livestock would be detected by inspectors, 

quarantine station officials or members of the brigades. In addition, the currently infested 

areas that are adjacent to Sonora, in both Sinaloa and Chihuahua, are currently 

undergoing eradication and control programs for Rhipicephalus spp., and livestock in 

these areas are currently subject to similarly rigorous inspection and treatment regimens. 

Illegal movement of livestock into Sonora

Another concern is the possibility that livestock could be smuggled into Sonora,

effectively bypassing the control measures in place at the border stations. This is 

unlikely due to the mountainous terrain along Sonora’s border with Chihuahua, the 

narrow geographic border with Sinaloa, which possesses very few easily navigable access 

roads, and targeted distribution and locations of inspection facilities along the border with 

Chihuahua and Sinaloa. In addition, documentation checks are performed at the many 

inspection stations along the interior roads in Sonora and livestock inspectors conduct an 

annual inventory of all animals located on premises in their zone and verify the origin of 

the animals, which increases the likelihood that smuggled animals would be detected 

subsequent to their entry into Sonora. Any violations in movement or documentation 

would likely be detected and would result in fines and possible forfeiture of livestock, 

providing a strong negative incentive for attempting illegal movement. It can be 

expected that these measures would be sufficient to both deter and detect illegal 

movement of livestock infested with Rhipicephalus spp. ticks. 
51

Discussion

The system of transit guides, tick inspection, and dipping or spray treatment associated 

with animal movement into and within Sonora has proven successful in preventing the 

introduction of Rhipicephalus spp. ticks into Sonora from other States or from the buffer 

zone region in southern Sonora. The procedures for entry into Sonora include tick 

inspection and treatment of all animals, as well as verification of information contained in

all required movement documents as specified under the Animal Health Federal Law and 

NOM-019-ZOO-1994. These procedures are strictly followed by the inspection 

personnel and, in the event that ticks are detected on any animals, on-site quarantine is 

imposed until elimination of the tick(s) is accomplished and investigation of the origin of 

the animals is conducted. Personnel involved in the documentation and livestock 

inspections, as well as those manning the dipping vat stations, were found to be 

knowledgeable and professional during the multiple site visit reviews. 

Although the possibility that livestock could be smuggled into Sonora, allowing them to 

bypass the inspection and dipping procedures required upon entry, cannot be entirely 

excluded, this is unlikely due to the presence of multiple inspection and dipping stations 

located along most of the navigable roads into Sonora, such as line baths, quarantine 

stations, and zoosanitary cord stations and routine inventory audits conducted by local 

livestock inspectors.

Because Sonora is adjacent to some tick-infested regions it is possible that wildlife 

harboring Rhipicephalus spp. ticks could enter into Sonora, most likely in the buffer zone 

area. Because these ticks prefer cattle hosts, it is likely that any ticks would move to 

cattle and be detected and/or treated as a result of enhanced surveillance and treatment 

measures in place in the buffer zone. 

Facilities at the various inspection and dipping facilities were found to be in good overall 

condition, possessing all necessary infrastructure. Significant improvements to the 

facilities have been made in response to previous site visit recommendations. 

The inspectors at the dipping vat facilities were knowledgeable, professional, and 

conscientious. Supervisors were likewise knowledgeable and responsive to issues 

requiring correction. Routine actions, such as aeration of the dipping vat solution, 

maintaining records of animal movement, and management of acaricidal solution were

carried out as required in Federal and State regulations and procedures. Record keeping 

was excellent and documents from different sources (i.e. lab results, monthly reports, and 

registries) were consistent with each other. 

The concentration of acaricide in the dipping vat solution and pH levels were improved 

from previous site visits, with most sample results in the effective range; however the 

concentration levels were still highly variable from one sample to the next, possibly due 

to the delay in receipt of sample analysis results and the implementation of recommended 

changes after several re-charges and possibly replacement of dipping vat solution had 

already occurred, causing a boomerang effect. 
52

The lengthy turnaround time for receipt of results of acaricidal solution analysis is cause 

for concern as this could potentially result in the treatment of cattle with inadequate and 

ineffective acaricidal solution for a prolonged period of time before the deficiency could 

be recognized. However, the speed and accuracy with which inspectors and supervisors 

representing the different types of dipping vat stations were observed to correct 

deficiencies in acaricidal solution when these deficiencies were noted significantly 

mitigated this concern.

8. Livestock demographics and marketing practices in the region 

As of the 2010 livestock inventory, there were over 1.5 million cattle residing in the State 

of Sonora. Most cattle farms in Sonora consist of beef operations, with a small number

of dairy or mixed operations. Sonora’s 2010 livestock inventory also identified over 

51,000 sheep, 22,000 goats, 73,000 horses, mules, and donkeys, and 400 farmed deer. 

The livestock were recorded as residing on over 46,000 premises [20, 71]. 

The primary market for Sonoran cattle is export. The vast majority of Mexican exports 

(over 99.9%) are destined for the United States, with a few dozen head going to Central 

American countries or Micronesia each year [54, 73]. 

Marketing and movement patterns of cattle

As discussed above, in section 7, the majority of cattle entering Sonora from other states 

are destined for further States, many to the domestic feedlots in Mexicali Valley, Baja 

California. Of cattle that are destined to remain in Sonora, most are intended for feeding 

for feeding (57-73% between 2008 and 2011), while a few are used for breeding, 

working, exhibition, or other purposes [54, 61]. 

Most of the steers that are exported from Sonora go to the United States for feeding

(90%) or to the States of Chihuahua or Baja California. Approximately 30% of heifers 

are exported to the United States as spayed heifers for feeding, while the remainder are

kept as replacement heifers or used for feeding within Sonora, Chihuahua, Baja 

California or Sinaloa [20]. 

The main auction market in Sonora operates twice a week and is located in the UGRS

corrals in Hermosillo. The market trades in all livestock and operates under the oversight 

of the UGRS, which maintains detailed records of the sales and movements of animals 

marketed through this auction. Most of the cattle marketed through the UGRS auction 

market are used for slaughter within Sonora with the rest going to Chihuahua or Sinaloa

[20]. 

Animal identification required for movement

Sonora’s herd identification program was started in 1997. The program is mandatory for 

any livestock moving off of their premises of origin and uses yellow metal ear tags 

imprinted with “SON” for Sonora followed by a five digit number, with the first two

digits signifying the municipality and the last three the premises of origin of the animal. 
53

This coding system allows for a unique number to be assigned to each herd in Sonora. 

All cattle that are moved in Sonora are required by State Law to be identified with a herd 

of origin ear tag. Livestock inspectors will only issue transit guides for cattle that have 

appropriate identification [54, 56].

Sonoran cattle may also utilize the National Cattlemen’s Association tag (Sistema 

Nacional de Identificacion Individual de Ganado, or SINIIGA). This tag costs more than 

the Sonora tag, but it provides access to subsidies and other benefits provided by the 

Cattlemen’s Association. This tag also provides a distinct code for the premises of 

origin, but is recognized across Mexico. Its first two digits are the letters “MX”, 

followed by a numerical code for the State of origin (Sonora’s code is “26”) and then 8 

additional digits denoting the specific premises [54].

Other tags used to denote test status for tuberculosis and brucellosis are recorded on the 

transit guide and other documents if present. The official test tags are serially numbered 

and may be required for certain movement purposes, but they do not identify the 

premises of origin and may not be substituted for Sonora or SINIIGA tags [54]. 

Annual Livestock inventory

Sonora’s livestock inspectors are responsible for conducting an inventory of all livestock 

premises and stock within their livestock zone each year. The inspectors use their 

knowledge of the local livestock industry as well as information from transit guides 

acquired by livestock farms to help insure that all livestock owners respond to the survey. 

They also verify that the numbers of stock provided are accurate (for instance, the 

number of new natural additions should be consistent with the number of breeding 

females on the farm, purchased additions or sales should align with the number of 

animals listed on transit guides leaving and entering the farms, etc.) [81].

The inventory includes the number of livestock on each farm by age, sex, and production 

type, as well as the brand and ear notch pattern associated with each farm. The survey is 

conducted every November. Livestock owners that do not provide the information will 

be in violation of the State and Federal law and may be fined accordingly. Additionally, 

animals will not be allowed to leave the premises (for sale, slaughter, export, etc.). If 

necessary, the livestock inspector may follow up with an on-farm visit if there are any 

discrepancies or concerns about the veracity of the data on the inventory form or if the 

form was not provided. And the information submitted on the inventory can also help 

inform the livestock inspector when issuing transit guides to ensure consistency of the 

information [54]. 

The annual inventory report is compiled by each livestock inspector. The owner keeps 

the original of the form and one copy each goes to the livestock inspector, the Livestock 

Committee, and the State offices where the information is compiled. Funding for the 

annual inventory is derived from fees paid by cattle farmers to the Livestock Association

for movement, export and slaughter of cattle. The results of the inventory can be used at 

the local level to verify that improper or illegal movement of livestock has not occurred, 

as it would be detected on inventory checks [54, 63].
54

Export of livestock to the United States

The number of cattle exported to the United States from Sonora varies each year, ranging 

from 200,000 to almost 300,000 between 2007 and 2010. The majority of these cattle, in 

excess of 90%, originate from the northern area of the State, outside of the buffer zone 

(see Table 1) [54].

Table 1. Cattle exports to the United States from Sonora, by origin

Year Northern 

Sonora

% Southern 

Sonora

% Total

2007-2008 197,449 93.13% 14,572 6.87 % 212,021

2008-2009 210,882 91.93% 18,509 8.07 % 229,391

2009-2010 256,480 91.41% 24,092 8.59 % 280,572

2010-2011 214,663 93.38% 15,207 6.62 % 229,870

Source: [61]

Sonora has three ports on the border with the United States: San Luis Rio Colorado, near 

the border with Baja California; Nogales, located centrally on the border; and Agua 

Prieta, located near Chihuahua. Currently, only Sonoran cattle are exported through 

Sonora’s U.S. ports. See Table 2 for a breakdown of cattle exports to the United States

by port [54].

Table 2. Cattle exports to the United States by port and type

Year SLRC Nogales Agua Prieta Total

9/2008-8/2009 18,937 123,826 86,628 229,391

9/2009-7/2010* 20,392 161,802 89,968 272,162

* partial year

Source: [60]

Most cattle exported to the United States from Sonora use the export corrals owned by 

the UGRS to congregate and process cattle prior to export. The corrals are also used as a 

feed lot for congregating and assembling groups of animals of similar types and sizes 

prior to exporting them as lots. Only Sonoran cattle are allowed to use these corrals, and 

their owners must be members of the cattlemen’s association. Cattle undergo spay or

castration surgery while at the corrals, and may receive brucellosis and tuberculosis 

testing and identification placement. The cattle also typically receive an injection of 

ivermectin shortly after arrival. If cattle come from the buffer zone of Sonora they 

receive an inspection for ticks (although they are not given additional dipping after 

leaving the buffer zone and receiving dipping at the Bahuises station and also the line dip 

bath). Cattle usually spend between 21-30 days at the corrals, which is enough time for 

testing to be completed and spay or castration incision to heal. Occasionally cattle may 

be kept for up to 180 days for feeding and fattening [54]. 

Whether or not cattle are exported through the UGRS corrals, they must all adhere to the 

same export requirements. The first step in the process is for the owner to have the cattle 
55

intended for movement tested for tuberculosis and brucellosis and to acquire tags 

denoting their test status (they must test negative for required tests in order to be moved). 

The owner must also procure a transit guide and certificate of origin prior to moving off 

of their premises and must have either the yellow SON or SINIIGA premises ear tags 

applied to all cattle that will be moved. If the cattle are coming from the southern part of 

Sonora (south of the Guasimas quarantine station) they must also have been inspected 

and treated for ticks prior to moving to the corrals [54]. 

The export facility has its own livestock inspection office, which is separate from the 

system of livestock inspectors located in local livestock zones throughout Sonora. 

Instead, this counts as one of the Centers of Livestock Inspection for High Movement (or 

CIGAMs) and it is staffed by employees of the State of Sonora. The inspectors check 

animals upon arrival for proper documentation and brands, presence of premises ear tags, 

and verify the number, sex, and type of animals. At the export corrals, they receive an 

ear tag denoting sterilization after spay or castration has been completed as well as a blue 

metal SAGARPA ear tag denoting brucellosis testing, which is an individually, serially 

numbered tag required for all cattle exported to the United States. All identification tags 

(premises, testing, spay/castration, export, etc.) are linked together in the database by the 

inspector. The inspector also verifies that appropriate testing has been conducted, 

dipping certificate is present if required, and that the export health certificate (zoosanitary 

certificate) has been procured. Once the animals are ready to proceed for export the 

inspector at the corrals will issue another transit guide for movement to the border [54]. 

There is another CIGAM inspection station located at the corrals immediately preceding 

the U.S. port. The inspector at this station checks to make sure that the appropriate 

documentation accompanies the animals and has not expired, verifies that the information 

contained in the documentation matches the animals (i.e. number of head, brand and tag 

numbers, etc.), verifies that tuberculosis and brucellosis testing has been conducted with 

negative results, and checks to make sure that a dipping certificate is present if one is

required. The inspector also performs a cursory visual inspection of animals in the load. 

If any documentation is missing the inspector will check with the owner, and will refuse 

the load if proper documentation cannot be supplied. If ticks or evidence of disease is 

detected on inspection the load will also be refused. Once the load has been approved the 

inspector cancels the final transit guide and forwards the cancelled document to the State 

offices where they will be entered into the electronic database and used to verify that the 

animals have arrived at the port. Only then are the cattle allowed to proceed for USDA 

inspection [54]. 

Discussion

Sonora’s herd identification system appears to be an effective way to track animals back 

to their herd and municipality of origin, allowing inspectors to determine the origin of 

livestock and thus their compliance with tick inspection and treatment requirements. In 

combination with the transit guide system and annual inventory, the identification 

program is an important and effective tool in Sonora’s tick control and identification 

arsenal. 
56

Export requirements for livestock intended for export to the United States provide 

another layer of checks and balances in the assurance that Sonoran livestock destined for 

the United States have received tick inspections and treatment as appropriate based on 

their origin and movement patterns.

9. Tick surveillance in the region

Routine surveillance

Tick inspections are regularly performed on livestock moving through and within Sonora 

as a part of routine movement requirements, particularly in livestock moving from or 

through the buffer zone or entering Sonora from other Mexican States. Although 

livestock moving entirely within the northern tick-free portion of Sonora are not required 

to receive a scratch inspection for ticks prior to movement, they do undergo a thorough 

health evaluation in order to receive a transit guide, which would potentially detect an 

infestation. Additional inspections are conducted at inspection and dipping stations 

encountered along transit routes as described in the preceding sections. 

During 2010, over 70,000 head of livestock moving with Sonora, most of them cattle, 

were inspected for ticks at one of Sonora’s internal quarantine stations (not including 

Bahuises, which primarily captures livestock moving north from the buffer zone and is 

addressed below). 

Inspections are also conducted on all animals presented for slaughter within Sonora as 

part of their ante-mortem evaluation. Sonora administers a veterinary inspection service 

in 24 slaughterhouses within the state, which account for the slaughter of 92% of the

cattle population. A visual check for ectoparasites is conducted by slaughter plant 

officials as part of the ante-mortem inspection procedure at these slaughter plants. In the 

event that ticks are detected on animals intended for slaughter, the livestock inspector

assigned to the slaughterhouse is informed, the tick(s) is collected and submitted to the 

CENAPA laboratory, and the State authorities are informed of the submission through 

the regional supervisor [20, 60].

National tick survey

A tick survey is conducted across Mexico each year. Although the primary objective of 

the survey is to identify Rhipicephalus spp. ticks, all detected ticks are collected and 

submitted for analysis. Livestock premises are selected based on a sampling scheme 

developed by the Department of Epidemiology and Risk Analysis of the DGSA. The 

study design incorporates a 99% confidence level of detection among herds at a 

prevalence of 1% and a within herd detection confidence level of 95% and a prevalence 

of 10%. Premises containing at least 60 head of cattle are eligible for selection, based on 

random sampling. Sixty head, selected randomly, are sampled from within each herd. 

During the 2010 sampling year, 479 livestock premises were targeted for sampling in 

Sonora, with 481 premises actually sampled (two additional premises were sampled in 

Bacoachi municipality). All of Sonora’s 72 municipalities were represented in the study 

[62, 71, 82]
57

A number of ticks were identified on Sonoran cattle during the 2010 study; however 

none were Rhipicephalus spp. (it was this study that found Rhipicephalus microplus in 4 

herds in the buffer zone in 2009). Ticks found during the 2010 survey included:

Otobius megnini on 252 premises; Rhiphicephalus sanguineus on two premises; 

Amblyomma cajennense and A. maculatum on one premises each; and Dermacentor

albipictus on six premises [62].

Enhanced surveillance in the buffer zone

Additional surveillance activities for Rhipicephalus spp. ticks are conducted within 

Sonora’s buffer zone. Approximately 181,000 of Sonora’s 1.5 million cattle reside in the 

buffer zone. The extra measures are implemented due to the region’s proximity to 

potentially infested areas, particularly in those municipalities and premises immediately 

adjacent to potentially-infested areas [71]. 

Both active and passive surveillance measures are carried out in the buffer zone. Passive 

surveillance activities are conducted in much the same manner as in the rest of Sonora, 

consisting primarily of tick inspection by local livestock inspectors or line dipping vat or 

quarantine station officals as a component of livestock movement. The difference in the 

buffer zone is that tick-related movement requirements are more stringent than in the rest 

of Sonora. All livestock moving within the buffer zone must receive an inspection for 

ticks as part of their movement requirements, and if departing the buffer zone for the 

northern part of Sonora they must also receive a tick inspection and treatment at the 

Bahuises quarantine station, located at the northernmost edge of the buffer zone. In 

addition, livestock moving from areas adjacent to the tick-infested regions of Sinaloa and 

Chihuahua must also receive an inspection and treatment at one of the line dipping vats

before movement, and if leaving the buffer zone are also subject to an additional 

inspection and treatment at the Bahuises quarantine station. Approximately 30% of cattle 

in the buffer zone reside in this area and thus are subject to two tick inspections and 

treatments prior to movement out of the buffer zone [20, 54].

Between 11,000 and 12,000 head of livestock were inspected annually at line dipping 

vats in the buffer zone from 2008 to 2010 either as part of their movement requirements 

within the buffer zone or in preparation for moving out of the buffer zone. Almost all of 

the inspected animals were cattle, with a few horses included. Additionally, 

approximately 47,000 livestock (again, mostly cattle, but also including a few horses, 

sheep, and goats) originating from the buffer zone were inspected and treated at the 

Bahuises quarantine station during 2010. There is some overlap between livestock 

inspected at the line dip bath facilities and those inspected at the Bahuises quarantine 

station for those animals moving out of the buffer zone from higher risk areas, which 

requires two inspections. Livestock from the buffer zone are also subjected to antemortem inspection for ticks and other ectoparasites upon presentation for slaughter as are 

those in the rest of Sonora [20, 54]. 

Error! Not a valid link.Active surveillance for Rhipicephalus spp. ticks in the buffer 

zones consists of a number of supplemental activities, including routine inspection and 

treatment for ticks on high risk premises and inspection and treatment of any livestock 

within the perifocal zone of previously infested premises by livestock inspectors. These 
58

cattle also receive routine injections with ivermectin (in a formulation labeled for tick 

control) two to three times per year, particularly if they will be in pasture and inaccessible 

for tick inspection for part of the year. High risk premises consist of properties that are 

adjacent to or straddle the border with Sinaloa or Chihuahua; there are currently 66 of 

these premises in the buffer zone, representing approximately 31,000 head of cattle. In 

addition to movement inspections, cattle residing on high risk premises are also inspected 

on-farm at least once a year, with any quarantined premises inspected every 21 days [54, 

62, 71]. 

 

There are six special livestock inspectors, directly employed by Sonora, that team up in 

pairs and form brigades to conduct the active surveillance activities on high risk premises 

(in addition to 64 regular livestock inspectors in the buffer zone). The special inspectors 

all have portable chutes and treatment equipment that they can carry with them in order 

to conduct tick inspections and treatments on-farm. In premises that straddle the border 

with Sinaloa, they also work alongside Sinaloan employees to assure that tick inspection 

and control activities are conducted on both sides of the border [54, 62]. 

Discussion

Routine surveillance for Rhipicephalus spp. ticks practiced throughout Sonora is 

comprised of several overlapping activities, including general health inspections 

performed by local livestock inspectors prior to movement of livestock off of the farm, 

more rigorous tick inspection by livestock inspectors prior to certain types of movement, 

inspections while in transit at quarantine stations or line dipping vats, ante-mortem 

inspection at slaughter, and annual nationwide tick surveys. 

Supplemental measures employed in the buffer zone include additional tick inspection 

opportunities for livestock during movement, both at the Bahuises quarantine station at 

the northern perimeter of the buffer zone and at the line dipping vats located within the 

buffer zone. The increased density of inspection and dipping stations located in the 

buffer zone, along with supplemental dipping requirements create a more robust passive 

surveillance program than is practiced throughout the rest of Sonora. Enhanced on-farm 

inspections and treatment of animals on high risk, quarantined, and nearby premises are 

also conducted two to three times throughout the year.

The overlapping surveillance measures used to detect ticks in Sonoran livestock are well 

organized and implemented and appear to be effective, as has been demonstrated by the 

periodic identification of ticks in Sonora’s buffer zone. 

10. Diagnostic laboratory capacity

The National Center for Animal Health Verification Services (CENAPA), located in 

Morelos, Mexico, is the national reference laboratory for parasitic diseases and residues. 

It operates under the DGSA within SENASICA. Currently, this is the only laboratory 

used by Sonora in the identification of ticks collected from livestock and the analysis of 

acaricidal solution. The laboratory was created in 1976 as the National Animal 

Parasitology Center in order to provide support to the National Campaign against Cattle 
59

Tick. It has since been restructured, and currently includes offices overseeing 

ectoparasites and hematophagous flies, hemoparasites and helminthes, animal feeds and 

medicines, and toxic residues [83]. 

In October 2000 the United Nations Food and Agriculture Organization declared 

CENAPA as the Reference Center for the Resistance of Ticks to Pesticides for Central 

America and the Caribbean. The purpose was mainly to provide diagnostic services for 

the detection of resistance in Rhipicephalus spp. ticks, as well as training of Mexican, 

Central American and Caribbean technicians on resistance [83]. 

The Ectoparasite and Diptera Office of CENAPA conducts activities related to ticks, 

bloodsucking flies, and bees. This office provides speciation of preserved ticks as well as 

the acaricide resistance profile of live ticks that are submitted by livestock inspectors, 

quarantine officials and other animal health personnel in Sonora. This office also 

conducts testing of acaricide samples to determine their effectiveness, conducts 

biological verification of acaricide effectiveness in order to license their use in Mexico, 

and maintains references strains of Rhipicephalus spp. ticks. In addition, staff from this 

office provide training to field staff in the detection of ticks and maintenance of acaricide 

solution [83]. 

An important function of this office is evaluating and monitoring changes in the acaricide 

resistance of ticks submitted by field personnel throughout Mexico in collaboration with 

the National Campaign against Cattle Fever Ticks in order to identify zones that are 

believed to be at high risk for the development of resistance to the various acaricides 

currently in use in Mexico. Methodologies used in the characterization of resistance 

include the Adult Immersion Technique (AIT), Larvae Package Technique (LPT) and 

Stone’s Technique. For analysis of acaricide levels ultraviolet/visible spectrophotometry 

is used for coumaphos and high resolution liquid chromatography is used for amitraz [60, 

83]. 

Employee training in the analysis of acaricide samples is provided by a number of 

sources, including suppliers of analytical equipment, employees at other similar 

laboratories (usually international laboratories) that perform the same functions, and 

national laboratory agencies, including the Mexican laboratory accreditation agency, 

National Center of Standards and Measurements, and Department of Labor. Quality 

assurance audits are provided by external agencies, including the Mexican Accreditation 

and Standardization and Certification agencies. The audits take place on an annual basis 

[71].

During multiple site visits conducted by APHIS it was noted that the turnaround time for 

receipt of laboratory results for acaricide solution evaluation was cause for concern. In 

some of the quarantine stations evaluated during the 2011 site visit, results were not 

received until up to 30 days after the sample was collected. Part of this delay was 

reportedly due to transport time to the laboratory [54, 60, 63, 72].

Discussion
60

Although the ability of the CENAPA laboratory to provide tick speciation and 

characterization services and evaluate acaricide solution samples appears to be sufficient, 

the delay in receipt of laboratory results, particularly the analysis of acaricide samples, is 

a significant concern due to the potential that cattle could be treated with inadequate 

acaricidal solution for extended periods of time without the knowledge of inspectors

(although, as mentioned previously, dipping vat management practices greatly mitigated 

this concern). The APHIS evaluation team recommended that either additional

laboratory facilities or improved policies are needed in Sonora to more quickly and 

effectively return laboratory analysis results for tick dipping solutions used at tick 

dipping stations and quarantine stations in Sonora. 

11. Emergency response capacity

Sonora contains a State Emergency Group for Animal Health (Grupos Estatales de 

Emergencia en Salud Animal, or GEESA) which includes members from Federal, State 

and private sectors trained in various disciplines in animal health. This group is 

responsible for organization and training of personnel at all levels to respond to multiple 

animal health emergencies, not just those related to Rhipicephalus spp. tick incursions 

and also with organization and oversight of emergency response activities. Personnel 

from several different areas of animal health with different backgrounds are included in 

the response team. The scope of the group includes surveillance, diagnosis, and 

movement control of not only animals, but also products, byproducts, vehicles, and 

people. The group currently consists of 32 members [20, 54, 60].

All emergency response individuals (including recent veterinary graduates) receive 

training from GEESA at different levels based on their experience and the amount of 

responsibility they would have during an animal health emergency. The first level of 

training provides instruction on the recognition of exotic animal diseases plus 

information on the planning documents and operations of the emergency response 

system. This training is broadly targeted to all recent or imminent veterinary graduates. 

The next three levels of training include additional information combined with tabletop 

exercises and involve increasingly specific and complex information designed for 

individuals with increasing levels or responsibility in the event of an animal health 

emergency. The final two levels are intended for new and returning GEESA members. 

A specific tabletop exercise for Rhipicephalus spp. ticks is included in the training of 

GEESA members [60]. 

The director of the GEESA is the regional coordinator for the United States-Mexico 

Commission for the Prevention of Foot-and-Mouth Disease and Other Exotic Animal 

Diseases (Comision Mexico-Estados Unidos para la prevención y control de la fiebre 

aftosa y otras enfermadades exoticas, or CPA). The CPA operates within the DGSA of 

SENASICA as part of the National System for Emergencies in Animal Health 

(Dispositivo Nacional de Emergencia de Sanidad Animal, or DINESA). The mission of 

the CPA has expanded beyond foot and mouth disease since its inception and its 

functions currently include the prevention, detection, control and eradication of exotic 

pests and emerging diseases of animals, as well as the protection public health. The CPA 
61

prepares and maintains contingency plans and procedural documents on the control and 

eradication of exotic diseases and implements emergency operations through DINESA. 

It also oversees laboratories that are involved in the detection of emerging and exotic 

diseases and pests, promotes disease detection and reporting activities, and provides 

training and technical updates to staff at various levels of emergency response. DINESA 

responds to a broader range of animal health concerns, including endemic disease events 

and natural disasters involving animal health consequences [20, 84, 85]. 

The funding for response to incursions of Rhipicephalus spp. ticks in Sonora is derived 

from contributions made by Federal, State, and private partners. As of 2010, the amount 

available in this fund was estimated at approximately $1,160,000 MX pesos 

(approximately $100,000 USD). Additional funds could also be made available by the 

Federal government as needed [20, 60]. 

Sonora’s rapid and effective response to the most recent incursions of Rhipicephalus spp. 

ticks into the buffer zone indicate that their emergency response system is able to respond 

quickly in containing and controlling the infestation. 

Discussion

Sonora appears to have an adequate system for responding to tick incursions. The Staterun GEESA has ample participation from individuals within many Federal and State 

agencies as well as different sectors of private industry. Training is applied broadly in a 

way that incorporates different levels of participation into reporting and response 

activities. Evidence of the effectiveness of Sonora’s emergency response capabilities 

with respect to Rhipicephalus spp. tick incursions has been demonstrated within the 

buffer zone in recent years. 

Conclusions

APHIS concludes that the likelihood that Sonora is currently infested with or will become

infested with Rhipicephalus spp. ticks is very low.

The northern region of Sonora is desert-like in climate and does not support the survival 

of Rhipicephalus tick spp. eggs. Consequently, this area has historically remained 

naturally free of Rhipicephalus spp. ticks. The southern tip of Sonora, near its border 

with Sinaloa, comprises a buffer zone, which is similar to the permanent tick quarantine 

buffer zone in South Texas in that it possesses a suitable climate for tick survival and 

occasionally experiences tick incursions.

Sonora has demonstrated that it has the infrastructure, personnel, and legal framework to 

prevent tick incursions into the free area through its program of routine tick inspection 

and dipping during movement from areas at risk for tick infestation. Inspection stations 

are strategically located along major transportation routes that enter into and traverse the 

State. The transit guide system requires identification of livestock during movement, 

linking tick inspection and treatment requirements to the origin and destination of 

livestock, ensuring that appropriate control measures are applied to all livestock engaged 
62

in transit. Furthermore, this system, in combination with the annual livestock census,

helps ensure that animals are not moved illegally, evading tick inspection and treatment 

procedures. An important component of Sonora’s successful eradication program is its 

Federal-State-private partnerships, which have been instrumental in accomplishing and 

maintaining Sonora’s Rhipicephalus-free status.

Four infestations of Rhipicephalus spp. ticks have been detected in Sonora since 

eradication was declared by SAGARPA in 1972; however, all occurred exclusively 

within Sonora’s buffer zone, were detected before the infestation became widespread, 

and were contained and controlled within time frames established by SAGARPA. 

Movement controls and additional tick inspection and dipping requirements are in place 

for livestock that move from the buffer zone into the historically tick-free region of 

Sonora. These controls have so far been able to restrict any incursions to the buffer zone.

If Rhipicephalus spp. ticks were to enter into Sonora, internal inspection requirements 

could be expected to detect these ticks on Sonoran livestock. Surveillance efforts have 

proven effective at detecting tick incursions in the buffer zone in a timely manner. 

Surveillance for Rhipicephalus spp. ticks is multi-pronged and comprehensive, and 

includes routine surveillance through an integrated system of tick inspection tied to 

movement, an annual tick survey directed by SAGARPA, and active inspections in high 

risk areas within the buffer zone. 

The most significant concern identified by APHIS is the delay in receipt of dipping vat 

acaricide analysis results at quarantine stations and line dipping vats. Laboratory analysis 

turnaround times evaluated during the 2011 site visit often exceeded three weeks from 

submission of sample to receipt of results. A mitigating factor is the adherence of 

dipping vat personnel to routine dipping vat maintenance, including recharging and 

replacing the dipping vat contents. In the case of high volume quarantine stations, these 

procedures may have been conducted multiple times before dipping vat analysis results 

were received, limiting the exposure of cattle to inadequate acaricidal solution, if it were 

present. Results reviewed in the dipping vat registries indicated that overall levels of 

acaricidal solution concentration were maintained within the effective range. However, 

despite the responsiveness of dipping vat personnel in conducting routine maintenance 

activities and undertaking recommended adjustments to the dipping vat solution, APHIS 

has concerns that this delay could potentially result in personnel unknowingly applying 

ineffective acaricidal solution to cattle for an extended period of time. 

Although APHIS has concerns about the delay in the turnaround time for acaricide 

analysis results from dipping vats, Sonoran officials and inspectors appear to maintain 

appropriate acaricidal concentrations in the dipping vats. This factor, when combined 

with Sonora’s low environmental suitability for cattle fever ticks, excellent detection and 

response capabilities, and overlapping movement control procedures, results in the 

finding of a very low likelihood that Sonora would become infested with Rhipicephalus

spp. ticks and that imported Sonoran cattle would introduce these ticks into the United 

States.
63

Exposure Assessment 

In accordance with the OIE, an exposure assessment consists of describing the biological 

pathway(s) necessary for exposure of animals and humans in the importing country to the 

hazards released from a given risk source and estimates the probability of the exposure 

occurring [25]. APHIS’ regulatory authority only extends to animal health; therefore the 

exposure assessment will focus on the exposure risks to animals. 

The importation of cattle into the United States from Mexico is currently permitted 

provided the cattle are subject to mitigations contained in 9 CFR 93.427, among others. 

The regulatory action proposed in this document recommends the removal of the 

requirement for tick dipping at the U.S. border port as written in Part 93.427(b)(1) of the 

CFR for cattle originating from Sonora. The proposed change will only affect the legal 

importation of cattle; therefore, this is the only pathway that will be addressed in the 

exposure assessment. Other possible pathways, including movement of illegal and stray 

cattle infested with Rhipicephlaus spp. ticks, movement of infested wildlife, and 

importation of tick-infested animal by-products and animal feed are not affected by the 

proposed action and will not be discussed further. 

For purposes of this exposure assessment, a release event or outbreak is defined as an 

infestation of Rhipicephlaus spp. ticks in one animal in the U.S. domestic cattle 

population outside the permanent (or temporary) tick quarantine zone in Texas. 

Alternatively, an outbreak could be defined as the diagnosis of bovine babesiosis in one 

animal in the domestic cattle population outside the tick quarantine zone. Cases of 

bovine babesiosis and Rhipicephlaus spp. ticks found during routine import procedures 

(i.e. scratch inspections at the port, quarantine facilities, etc.) or on livestock within the

tick quarantine zone will not be considered an outbreak.

Legal importation of cattle infested with Rhipicephlaus spp. ticks 

In order for an outbreak to occur in U.S. cattle as a result of legal importation of infested 

cattle under the proposed regulations, multiple failures in both Sonoran and U.S. tick 

detection and treatment measure would have to occur, and the cattle would have to end 

up in a suitable environment for tick survival. First, infested cattle originating from 

Sonora would have to be selected for export to the United States without being detected.

Tick inspection measures required at Sonoran inspection stations and as a component of 

Sonoran livestock movement requirements would then have to fail, as would any tick 

treatments required during movement to the U.S. border. On arriving at the U.S. border 

port, the infested cattle would have to pass a scratch inspection without detection of the 

ticks. Following importation, the infested cattle would have to be transported within the 

United States to an environment that favors the survival of Rhipicephlaus spp. ticks (refer 

to the Hazard Identification for further details). An adult female tick would have to feed 

sufficiently to produce eggs, drop from the imported animal and find a suitable 

environment to lay the eggs, and produce viable larvae, all in close enough proximity to 

U.S. cattle in order for the larvae to attach to a domestic cattle host. 
64

Based on the historic endemic range of Rhipicephlaus spp. ticks, climatic conditions, and 

general movement patterns of Mexican cattle, exposure of the U.S. cattle population to 

fever ticks, if they were imported on cattle from Sonora, would most likely occur in the 

southern United States. However, the variability of seasonal weather patterns, possible 

climatic changes, and livestock movement patterns within the United States could create 

suitable microclimates outside these parameters and allow pockets of Rhipicephlaus spp.

ticks to survive in unexpected or unprecedented regions of the United States. 

Approximately one million cattle are exported into the United State from Mexico per 

year. Cattle enter through various ports in Arizona, New Mexico and Texas. Although 

cattle from Mexico are shipped all over the United States, most end up in states where 

large amounts of cattle feeding occurs such as California, the central United States, and 

the southwest [86]. Thus, Mexican cattle could be commingled with domestic herds in 

regions that could sustain the life cycle of Rhipicephlaus spp. ticks. Sonora exported an 

average of 240,000 head of cattle to the United States per year between 2007 and 2010. 

Due to the many overlapping tick prevention and detection measures in place in Sonora, 

as well as at the U.S. border ports, combined with environmental and transmission 

requirements for successful movement of ticks to the domestic cattle population, APHIS 

considers the likelihood of an outbreak of Rhipicephlaus spp. ticks in domestic livestock 

resulting from the legal importation of undetected infested cattle from Sonora to be low. 
65

Consequence Assessment

In accordance with the OIE, the consequence assessment consists of describing the 

relationship between specified exposures to a biological agent and the consequences of 

those exposures. Direct consequences include animal morbidity and mortality, 

production losses, and public health consequences while indirect consequences include 

surveillance and control costs, trade losses, and adverse consequences to the environment 

[25]. This consequence assessment will consider both direct and indirect consequences 

of introducing the hazard under consideration into the United States. 

For purposes of this consequence assessment, an outbreak is defined as an infestation of 

Rhipicephalus (=Boophilus) spp. ticks in one animal in the U.S. domestic cattle 

population outside the tick quarantine zone. Alternatively, an outbreak could be defined 

as the diagnosis of bovine babesiosis (B. bovis or B. bigemina) in one animal in the 

domestic cattle population outside the tick quarantine zone.

Biological consequences

Direct consequences of an outbreak need to consider the biological consequences of a 

Rhipicephalus spp. tick infestation or bovine babesiosis. It is assumed that the U.S. 

domestic cattle population is a naïve, or non-endemic population, with a general lack of 

immunity to B. bigemina and/or B. bovis. If the cattle are found to be infested with 

Rhipicephalus spp. ticks in the absence of bovine babesiosis, morbidity and mortality are 

expected to be low. Although tick infestations can cause some morbidity, especially in 

the very young and immunodeficient, death is uncommon. Severe tick infestations can 

cause anemia, poor growth, decreased milk production, and damage to hides and skin. 

In contrast, bovine babesiosis can cause significant morbidity and mortality in fully 

susceptible populations. Morbidity is expected to be greater than 50% with older animals 

more affected than calves. Similarly, mortality rates will also be greater than 50%, 

perhaps approaching 90%, with B. bovis generally resulting in a more severe infection. 

Animals that do survive can remain persistently infected and can contribute to persistence 

of the disease if Rhipicephalus spp. ticks are also present. Additionally, those that 

survive have a slow recovery and production losses associated with severe weight loss, 

drop in milk production, and abortion can be expected. If bovine babesiosis becomes 

endemic in the population, morbidity and mortality rates will subsequently drop as cattle 

can develop lifelong resistance to a species after infection [26, 87]. 

Although the biological consequences of infestation of U.S. cattle with Rhipicephalus

spp. ticks are low, if the infestation were to lead to infection of the U.S. cattle population 

with bovine babesiosis, the consequences would be high, particularly in the early stages 

of the outbreak while the majority of cattle are susceptible to acute infection. 

Public health consequences
66

Although public health is not under the authority of APHIS, public health consequences 

will be briefly mentioned. Neither B. bovis nor B. bigemina are believed to be zoonotic, 

so transmission of the infection to people is not a concern [26]. 

Exposure to the acaricide chemicals, however, can result in public health concerns. 

Coumaphos is an organophospate that can cause acute toxicity to humans via 

cholinesterase inhibition. It can be fatal if swallowed and may be absorbed through the 

skin, mucous membranes and through inhalation [88]. Increased occupational exposure 

of animal health personnel to coumaphos during an outbreak of Rhipicephalus spp. ticks 

or bovine babesiosis in the United States would be expected. The general public could be 

exposed through ground and water contamination. However, personal protective 

measures and pesticide disposal protocols could be expected to mitigate both of these 

exposures. Personal protective equipment guidelines are stated in VS Memo 556.1 

Supplemental No. 11 titled, Use of Personal Protective Equipment (PPE) when Using 

Permitted Pesticides for the Control and Eradication of Cattle Ticks. Disposal guidelines 

are stated in VS Memo 556.1 Supplement No. 10 titled, Procedures for Storage and 

Disposal of Permitted Pesticides. 

Additionally, depending on the size of the outbreak, there may be psychosocial effects on 

farmers and the farming community as a result of loss of livestock and revenue associated 

with outbreak control measures. Loss of animals, particularly expensive or rare breeding 

stock, disruption to business due to quarantine measures and movement restrictions, 

economic burdens from revenue losses, and stress of uncertain financial future can result 

in increased stress and distress in people during animal disease outbreaks. 

A Rhipicephalus spp. tick outbreak would be expected to be isolated, with relatively 

limited numbers of producers affected and control measures would not likely include 

destruction of infested animals. Additionally, current measures could be expected to 

mitigate human exposure to pesticides used to treat the tick infestation. 

Economic consequences

It is likely that movement restrictions would be imposed in the event of a domestic 

infestation with Rhipicephalus spp. ticks, involving affected herds as well as neighboring 

and epidemiologically linked herds. In addition, enhanced surveillance, inspection and 

treatment measures would likely be undertaken by livestock authorities. Implicated 

state(s) may also be subject to movement restrictions or additional requires for entry into 

unaffected states, including additional inspections and/or dipping requirements. 

International trading partners could be expected to apply restrictions on live cattle from 

the United States and associated products, at least temporarily. 

Although difficult to accurately predict, the economic impact of a single outbreak is 

likely to be significant. In a report from the Agricultural and Food Policy Center at 

Texas A&M University, analysts constructed a model to forecast the economic impact of 

a relatively small Rhipicephalus spp. tick outbreak outside of the tick quarantine zone in 

Texas as well as a more extensive outbreak within the historic tick range of the United 

States. The annual cost for the small outbreak (defined as 3 infestations) in Texas was 
67

estimated at $123 million the first year and $93 million per year for subsequent years. For 

a 500 cow-calf herd, producer costs in the first year were estimated at $250 per head. 

Extending the outbreak to the 14 states that comprise the historic range of Rhipicephalus

spp. ticks would conservatively cost over $1.2 billion in the first year [89]. 

The FY 2010 budget for the Cattle Fever Tick Eradication Program was $13.1 million. 

Even a relatively small outbreak would far exceed the budgetary resources needed to 

control and eradicate Rhipicephalus spp. ticks. The burden of additional funding for 

surveillance, dipping and inspections, indemnity, new dipping facilities, acaricide 

acquisition and disposal mechanisms, etc. would likely be borne by producers, State 

Governments, and APHIS. Additional revenue losses from trade restrictions, both 

domestic and international, would be expected to cause additional damage the U.S. cattle 

industry. 

Environmental consequences

Environmental consequences resulting from a Rhipicephalus spp. tick outbreak would 

result primarily from the use of additional acaricide in an effort to control the infestation. 

If bovine babesiosis were to result from the infestation, increased consequences may also 

occur as a result of increased carcass disposal due to livestock mortalities. 

For acaricide disposal, human and animal exposure to spent dipping vat coumaphos in the 

environment (ground and water sources as well was dietary sources) are mitigated by 

U.S. regulations. Currently, bioremediation (aerobic microbial degradation) of spent 

dipping vat water followed by storage in shallow, concrete lined evaporation ponds is 

required to be employed at U.S. Cattle Fever Tick Eradication Program dipping vats in 

the disposal of spent coumaphos solution [88, 90, 91]. Disposal guidelines are stated in 

VS Memo 556.1 Supplement No. 10 titled, Procedures for Storage and Disposal of 

Permitted Pesticides. Because of these regulations the environmental impact of disposal 

of spent dipping vat acaricidal solution would likely be low.

Mortalities would be expected to occur in the event of exposure of U.S. cattle to bovine 

babesiosis, at least initially, as this population is considered to be fully susceptible to B. 

bigemina and B. bovis. In addition, increased dipping of cattle as part of the enhanced 

tick control measures could be expected to lead to a small amount of morbidity and 

mortality in treated cattle, particularly young or weak animals, potentially as a result of 

drowning, aspiration pneumonia, or toxicity. 

Disposal of the additional carcasses could potentially have an effect on air quality (if 

incineration is used) or ground water (if burial is used). However, the expected number 

of additional mortalities is expected to be low. In addition, both State and Federal 

regulations would govern incineration and burial, likely minimizing or eliminating the 

effect of carcass disposal on air quality and ground water contamination, so the ultimate 

impact to the environment could be expected to be low. 
68

Risk Estimation

Risk estimation consists of integrating the results from the release assessment, exposure 

assessment, and consequence assessment to produce an overall measure of risk associated 

with the hazards identified at the outset of the evaluation. Thus, risk estimation takes into 

account the whole risk pathway from hazard identified to the unwanted event [25, 92].

APHIS concludes from the release assessment that the likelihood that Sonora is currently 

or will become infested with Rhipicephalus spp. ticks is very low. This is due in part to 

the historical absence of Rhipicephalus spp. ticks from Sonora as a result of its climate, 

as well as its robust inspection, treatment, and movement programs, which are largely 

successful due to the coordinated involvement of Federal, State, and private entities in 

Sonora’s tick eradication and prevention programs. Given that APHIS considers the risk 

of Rhipicephalus spp. tick infestation in Sonora to be very low, APHIS consequently 

concludes that removal of the requirement that Sonoran cattle receive a dipping vat 

treatment at the Sonoran port of entry into the United States is not likely to result in the 

exposure of U.S. cattle to these ticks. 

APHIS concludes from the exposure assessment that the risk of Rhipicephalus spp. ticks 

reaching the U.S. cattle population is low. Sufficient exposure would require the 

occurrence of a number of sequential adverse events following the importation of 

undetected Rhipicephalus-infested cattle into the United States. These would include a

failure of tick mitigations applied at the U.S. border ports, transport of imported cattle to 

an environment that could support the survival and replication of these ticks, and contact 

of the resulting larval ticks with domestic cattle. The combined risk of release and 

exposure is, therefore, extremely low. 

The consequences of Rhipicephalus spp. ticks entering into the United States, resulting in 

a tick outbreak would likely result in the implementation of a control campaign, which 

could be costly, especially if it becomes extensive. In contrast, if the tick infestation 

resulted in a resurgence of bovine babesiosis in the indigenous cattle population, the 

additional consequences in terms of cattle morbidity and mortality could be significant. 

Additionally, movement restrictions within the United States, as well as export trade 

losses, could be expected to add to these consequences.

In summary, although the consequences of an outbreak of Rhipicephalus spp. ticks in the 

U.S. cattle population could be costly, especially if associated with bovine babesiosis, 

APHIS considers the risk of Rhipicephalus-infested cattle entering the United States from 

Sonora resulting in exposure to U.S. cattle, even with the removal of the tick dipping 

requirement at the U.S. border port, and subsequent transmission of bovine babesiosis to 

the U.S. cattle herd to be very low. 
69

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