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FMD Epidemiological surveillance: 

Serological sampling 2011

Introduction:

The Directorate for Epidemiology, dependent of the National Directorate of Animal 

Health of SENASA, designs these studies which are prepared and advised by the 

Integrated Epidemiology Advisory Committee, made up by a group of epidemiologists of 

the Official Service and other agencies (INTA, CONICET and faculties of veterinary 

Schools).

The regulatory framework to carry out this study responds to the current international 

regulation on FMD in accordance with the Terrestrial Animal Health Code of the World 

Organization for Animal Health (OIE), SENASA carries out surveillance in conformity 

with articles 8.8.40 to 8.5.46; with the objective to demonstrate absence of disease, both in 

free zones with vaccination, as well as where vaccination is not practised.

In the zone with vaccination absence of virus circulation is demonstrated and immunity 

given by the vaccine at a cattle population is estimated.

As to operational sample collection and delivery, these are in charge of the regional local 

veterinarians of SENASA, while the diagnosis is carried out in the Animal Laboratory of 

the Directorate for Laboratories and Technical Control (DILAB-SENASA).

Objetives:

a) To detect virus circulation or infection by the foot-and-mouth disease virus (FAV) 

in the national territory.

b) To estimate the population immunity level for foot-and-mouth disease in the cattle 

population in the area with vaccination.

Variables to measure:

a) Infection or virus activity indicators: presence of antibodies against non-structural 

proteins (NSP) in cattle and against structural proteins (SP) in species other than 

cattle.

b) Immunity level in the vaccinated population: in cattle that previously were negative 

to the NSP tests, the values of antibodies against SP for types of virus present in 

the vaccine are determined
DNSA – Dirección de Epidemiología y Análisis de Riesgo - Programa de Fiebre Aftosa 

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Sampling framework: 

This study is carried out throughout the country, although due to the geographical 

diversity, climates and production systems, the territory is divided into zones in regard to 

vaccination implementation. It is for this reason that the vaccination zone is subdivided 

into sub-zones (1, 2 and 3). Based on this zoning for zones 1 and 2 according to the 

bovine density, majority in the first one, while in the second one extensive production 

systems predominate. Zone 3, according to the regionalization of the FMD Eradication 

Plan , corresponds to Patagonia North A; created with the objective of protecting the rest 

of the Patagonia (Patagonia North B and Patagonia South) that is separated from the rest 

of the country and is treated as a special zone without vaccination. Figure 1 shows the map 

with the different sub-zones.

Figure 1: Map with the zoning of Argentina.

Sample size:

The objective of this sampling consists in the detection of an event in each of the zones 

and was carried out in two stages.

The considered assumptions are represented in table 1.

References:

1. EAST ZONE

2. WEST ZONE

3. PATAGONIA NORTH A ZONE

4. PATAGONIA NORTH B ZONE AND PATAGONIA

SOUTH

2

1

3

4
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Table 1. Assumptions considered in this sampling

Prevalence of infected 

herds

1%

Prevalence of infected 

animals

10%

Confidence 95%

From these assumptions 350 livestock farms were selected in each zone, where 28 animals 

were sampled in each establishment.

Species and categories of sampled animals: 

The sampled species were cattle, sheep and goats. All of different categories or ages, 

according to each zone:

 Zones with vaccination (1, 2 and 3): 

o Cattle: 28 animals by each establishment : 

 17 animals of category 1 (6 to 12 months of age).

 11 animals of category 2 (12 to 24 months of age).

o Sheep/goats if any, in each establishment: 

 10 animals 6 to 24 months of age. 

This is because the production areas of these species coincide with marginal 

zones or of low receptivity, making distribution of these populations very 

irregular.

 Zone without vaccination (zone 4): 28 animals of any of the susceptible species 

(bovine, ovine or caprine animals) according to the stocks of the selected farm. 

Measure adopted due to the non-vaccination condition, added to the geographical 

and climatic diversity.

Diagnostic tests: 

All of the samples are processed at the SENASA central laboratory (Directorate for 

Laboratories and Technical Control, Martínez, Buenos Aires province), which is the FMD 

reference laboratory of the World Organization for Animal Health (OIE).

Cattle:

 ELISA 3 ABC-EITB (KIT NCPanaftosa) for the detection of antibodies against 

non-structural proteins (NSP) of foot-and-mouth disease virus (FMDV) as 

infection indicator. 
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 ELISA fl for the detection of antibodies against structural proteins (SP) of types 

O1 Campos, A2001 and C3 Indaial of FMDV, to estimate immunity in vaccinated 

populations. 

Sheep/goat:s: 

 ELISA fl for the detection of antibodies against structural proteins (SP) of types

O1 Campos, A2001 and C3 Indaial of FMDV, to estimate immunity in vaccinated 

populations. 

In regard to samples of esophageal-pharyngeal fluid (LEF) collected in reactor animals at 

initial sampling, these are processed by Complement Fixation Test at 50% in each of the 

two passages in BHK cell cultures.

Results of virus activity in the vaccination zone:

Table 2 and 3 show the number of bovine animals sampled in the zone with vaccination 

and the results obtained by categories are listed in the table 2 and 3. It is considered as 

reactor animal those whose sera were reactors to 3ABC and EITB ELISA tests. Table 4 

and 5 show the number of establishments sampled and the results obtained from 

sheep/goats.

Table 2: Number of sampled cattle in the zones with vaccination (zones 1, 2 and 3).

Zone No. of farms No. of cattle

1 350 9537

2 315 8065

3 332 7819

Total 997 25421

Table 3: Results to the ELISA 3ABC-EITB tests in cattle of the zone with vaccination, by 

category.

Animals in category 1 Animals in category 2

Zone sampled

 Reactors

sampled

 Reactors

No. % No. %

1 5794 0 0 3743 0 0

2 4771 1 0,02 3294 4 0,12

3 4795 0 0 3024 1 0,03

Total 15360 1 0,01 10061 5 0,05
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Table 4. Results to the ELISA fl tests for the virus types A2001, O1 Campos and C3 Indaial 

in sheep/goats of the zone with vaccination.

Zone No. farms No. sheep and/or goats

1 216 2111

2 180 1719

3 168 1928

Total 564 5758

Table 5. Farms and samples collected of sheep/goats.

Zone No sheep and/or goats No. of reactors

1 2111 0

2 1719 0

3 1928 0

Total 5758 0

In regard to the number of sampled farms, there were some zones where sample collection 

could not be concluded as requested. This was due to severe weather problems (drought) 

that affected large areas of the country, making it impossible to keep the animals in corrals

due to extreme weakness. However, the validity of the study was not affected given that a

larger number of samples than those requested in the design.

Figure 2 shows the map with the geographical distribution of the sampled cattle farms.

Figure 2. Geographical distribution of the sampled cattle farms.
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Figure 3 shows a map with the distribution of sampled farms with sheep/goats in the zone 

with vaccination (zones 1, 2 and 3).

Figure 3. Geographical distribution of the sheep/goats sampled farms

Figure 4 shows the geographical location of the farms that resulted with at least one bovine 

reactor to the serological tests carried out.

Figure 4. Geographical distribution of the farms with bovine reactors to ELISA 3 ABCEITB tests.
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Supplementary Studies:

When there was an animal positive to the confirmatory tests, the official laboratory 

informed the fact to the Epidemiology Directorate for the result and, according to the OIE 

Terrestrial Code, in that farm where the animal was found, a follow-up study was carried 

out. For this purpose, the official veterinarian of the jurisdiction corresponding to the 

mentioned farm, where the supplementary investigation was carried out was informed, 

which consisted in visiting the farm and interviewed the owner or the person responsible 

for the animals, movements of susceptible animals (entries and exits) were studied, 

additionally a supplementary serological study was carried out, which consisted in:

• Clinical inspection and new serology of the same group of animals of the first 

sampling.

• Clinical inspection and serology of a group of contact animals of the first lot.

• Clinical inspection and serology of a group of non-vaccinated susceptible animals 

(sheep/goats), in case they are available at this farm or at a neighboring farm.

• Extraction of esophageal-pharyngeal fluid (LEF) for PROBANG of the reactor 

animal. This sample is repeated in 21 days

In each of the 6 investigated farms, where there was a single reactor animal, indicated 

activities were carried out. In total 474 supplementary serum samples were collected and 

LEF samples were collected in those cases where the reactor animal was located.

In none of these investigated farms there was evidence of virus circulation or of disease, 

both by clinical inspections and surveys, supplementary serology or virological surveillance 

(LEF).

Results in the zone without vaccination:

The zone without vaccination (zone 4) is recognized by the OIE as a "FMD Free Zone 

where Vaccination is not practised" and corresponds to Patagonia South and Patagonia 

North B.

The design applied in this zone included sample collection in bovine, ovine and caprine 

species. However, due to the predominance of sheep production in all Patagonia, in most 

of the selected farms only this species was sampled.

Table 6 details the number of farms and samples collected, by species, as well as the results 

obtained.
DNSA – Dirección de Epidemiología y Análisis de Riesgo - Programa de Fiebre Aftosa 

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Table 6. Farms and animals sampled and their results in zone 4 (without vaccination) 

Farms reactors % Animals reactors %

Sheep/goats 326 0 0 8753 0 0

Cattle 24

0 0

Category 

1

286 0 0

0 0

Category 

2

220 0 0

Total 350 0 0 9259 0 0

Figure 5 shows the geographical distribution of the sampled farms in zone 4 (zone without 

vaccination) with sheep/goats and cattle.

Figure 5: Geographical distribution of the sampled farms with cattle (blue) and 

sheep/goats (green) in zone 4.
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Conclusions: 

Through these activities of active surveillance, no evidence of virus circulation or of 

infection of FMD virus was found, by clinical inspections and surveys, supplementary 

serology or virological surveillance (LEF), both in the zone with vaccination as in those in 

where vaccination is not practised.

In addition to these results, it is also taken into account other activities of epidemiological 

surveillance that are carried out across the country for the purpose of demonstrating the 

health situation in both zones in regard to FMD.

o Ante- and post-mortem inspection at the time of slaughter (approximately 12 

million cattle, 3 million pigs and 1 million sheep annually in establishment with 

SENASA inspection).

o Inspections at the time of FMD vaccination by trained personnel, two times per 

year in all the bovine population of the zone with vaccination.

o Inspecciones oficiales en diversos controles efectuados por personal de campo de 

SENASA o veterinarios acreditados:

o Official inspections in various control posts carried out by SENASA field staff or 

accredited veterinarians:

o Herds to slaughter for export.

o Auctions, fairs and exhibitions

o Inspections for transfer to zones of different status in regard to tick.

o Inspections by other health programs (sheep scab program in Patagonia,

for example).

o Inspections for movement of animals in protected areas (exit of animals in 

High Surveillance Zone; entry of susceptible animals to Patagonia North).