Equine Disease Quarterly Newsletter

5poor biosecurity. Many evacuations must occur
rapidly and at night, which produces additionalrisks. Early evacuation is strongly suggested using
a previously prepared plan that addresses capture,
movement to a safe area, and horse identification.

CONTACT:John Madigan, DVM, MS Diplomate ACVIM, ACAW,Distinguished Professor-Emeritus
jemadigan@ucdavis.edu
530-304-1212
University of California-Davis
Davis, California

Presorted Standard
US Postage Paid
Permit 51
Lexington KY

Department of Veterinary Science
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky 40546-0099
Address Service Requested

F U N D E D B Y U N D E R W R I T E R S AT L LOY D ' S , LO N D O N

KENTUCKYOCTOBER 2020
Volume 29, Number 4

Rhodococcus Equi-associated Extra-pulmonary DisordersRhodococcus equi is a ubiquitous environmental bacterium that causes one of the costliest
diseases on equine breeding farms. The most common disease manifestation is pneumonia in young
foals. Infection with R. equi appears to occur inthe first few days of life and remains subclinicalfor several weeks. Many foals eliminate infection
on their own, while others develop respiratory
disease. Management of rhodococcosis can befurther complicated by the development of extrapulmonary disorders (EPDs).
Extra-pulmonary disorders refer to any clinical manifestation of rhodococcosis other thanpneumonia. A large study estimated that 74% of
infected foals had at least one EPD. In many cases,
EPDs were not diagnosed until postmortem examination. In this study, survival was significantly
lower in foals with EPDs. Factors that influence
development of EPDs are not completely understood, but it is generally accepted that EPDs areindicative of a more severe infection. EPDs canpose a major diagnostic challenge and warrant
thorough evaluation of any sick juvenile foal.
Identification of EPDs can aid in selection of appropriate therapy, monitoring response to therapy,
and prognostication.
Clinical signs of R. equi pneumonia rarely develop before three to four weeks of age. While bloodwork and ultrasonography can increase suspicion
of infection, a tracheal wash provides a definitive
diagnosis. Suspicion of R. equi pneumonia should
prompt investigation for EPDs elsewhere in thebody.
Intra-abdominal abscessation is one of the mostcommon EPD. It is suspected that R. equi spreads
hematogenously or is ingested in sputum to cause
abdominal lesions. Abscesses are best diagnosed via
ultrasonography, highlighting the importance ofabdominal ultrasonography in foals with pneumonia. Alternatively, abdominal abscessation might
only manifest as a recurrent fever or unexplained

high white blood cell count. Generally, a sample
cannot be obtained from abscesses to confirm R.
equi involvement. Presumptive diagnosis is madebased on the foal’s age and concurrent pneumonia.
Successful treatment of abscessation is possible,
but foals with intra-abdominal abscesses are ata significantly greater mortality risk. Survivability seems to decrease with increasing size ofabdominal abscesses. Treatment of abdominal R.
equi infection includes provision of a long courseof antimicrobials. Surgical debulking or resection
typically is not possible due to attachments of theabscess to adjacent structures.
R. equi can spread hematogenously and resultin osteomyelitis. Clinical signs of affected foals include lameness, ataxia, and recumbency. Retrieving
diagnostic samples from affected sites for diseaseconfirmation can be difficult. Osteomyelitis may
be best diagnosed via radiography or computed tomography. Successful treatment has been reported,but prognosis is typically considered poor. Other
documented sites of R. equi infection include thecentral nervous system, kidney, and liver.
Polysynovitis is perhaps the most commonly
observed EPD. It is characterized by symmetricjoint effusion without lameness. R. equi is rarely
cultured from affected joints; this finding has longsupported a conclusion that this phenomenon isimmune-mediated. Recently, experimental infection of foals resulted in the isolation of R. equi fromsynovial fluid 14 days post-infection. This lends
support to a newer theory that polysynovitis isa septic complication of infection that might
actually result from hematogenous spread. In thesame study, experimental infection also resulted
in the isolation of R. equi from ocular fluid. Uveitis has also been considered immune-mediated.
Unlike polysynovitis, R. equi uveitis is strongly
associated with nonsurvival in foals. With both ofthese EPDs, a suspected hematogenous origin is
an interesting development in our understanding

C O M M E N TA RY
IN THIS ISSUEof the disease as many other EPDs appear to precipitate from bacteremia. The role of the immune
response in the development of EPDs should not
be discounted yet, as several reports exist of foals
affected by immune-mediated hemolytic anemia
associated with R. equi infection.
Extra-pulmonary disorders are frequently
encountered during the management of foals
infected with Rhodococcus equi. As current litera-ture suggests a septic process in the pathogenesisof polysynovitis and uveitis, it is logical to speculatethat the precipitation of most EPDs is a functionof bacteremia and the host’s immune response tosystemic infection.
CONTACT:
William Gilsenan, VMD, Dipl. ACVIM-LAIM(859) 233-0371
Rood and Riddle Equine Hospital
Lexington, KentuckyT

he COVID-19 pandemic has heightened theawareness of the horse industry regarding
Commentary
the potential introduction and spread of foreign
animal diseases (FAD). The human pandemic
International
highlights the importance of early detection,
Second Quarterlaboratory utilization of high capacity, validated
2020  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2diagnostic testing, and coordinated implementaAfrican Horsetion of a disease response plan. How would the
Sickness .  .  .  .  .  .  .  .  .  .  .  .  . 3national and international community respond toa pandemic of equine infectious disease?
National
The threat of an FAD entering the U.S. is a
Wildfires .  .  .  .  .  .  .  .  .  .  .  .  . 4 top concern of regulatory animal health officials.
These officials are responsible for implementing
Kentucky
mitigation measures to prevent introduction of a
Rhodococcus equi .  .  .  . 5 highly contagious or vector-borne disease agent.
Risk reduction includes pre-import testing andpost-import quarantine as well as testing of live
animals and animal products to ensure that diseases
with the potential to become widely disseminated
do not enter the country. FAD may be introduced
by an asymptomatic carrier, contaminated equipment, or an infected vector or reservoir host.
Should an FAD enter the country, private practitioners and equine owners would provide criticalsurveillance and hopefully its early detection. Any
individual suspecting an FAD should immediately
report the case to a local regulatory authority.
Once reported, an FAD diagnostician will visit
the premises within 24 hours of notification to
perform an onsite investigation, examine affected
College of Agriculture, animals, obtain appropriate samples for laboratory
Food and Environment testing, quarantine the animals and/or premises,
Department ofand implement disease control measures. If diVeterinary Scienceagnostic testing at the Foreign Animal Disease
Laboratory on Plum Island, NY, confirms an FAD,
then regulatory officials will implement movement
restrictions and disease eradication measures.
Unlike an outbreak of an endemic disease,
Lloyd’s—An internationalsuch as strangles or equine influenza, all members
insurance market forof the equine industry across the country would
bloodstock and otherspecialist insurance.

be impacted by an FAD outbreak. Confirmationof an FAD results in activation of a national response plan with coordination of state and federal
animal health officials. With detection of an FAD,
countries can prohibit entry of equids from the affected country and domestic movement of horses
is restricted. Restrictions may extend to equine
affiliated entities such as nutritionists, farriers,
equine dentists, and feed and hay suppliers.
The ultimate outcome following the introduction of an FAD depends on the response of regulatory officials in concert with the equine industry.
Preparedness, prompt response, and collaboration
are key to success. Unfortunately, domestic equinedisease outbreaks in recent years have shown theequine industry is underprepared due mainly tolimited implementation of biosecurity measuresand insufficient use of diagnostic testing. Furthermore, limited resources at national and local levels
to address equine disease issues result in the inability
to focus on the development and training involvedin a national equine FAD response plan. Lastly,
segmentation of different sectors of the equine
industry leads to challenges in communication andcollaboration and slows the response to an FAD.
The equine industry has a unique opportunity
to learn from the current human pandemic andenhance equine FAD preparedness and response.
Equine stakeholders can reach out to local andnational regulatory authorities to prioritize the development of an equine FAD response plan, which
focuses on business continuity while protecting thehealth of the nation’s equine population.
CONTACT:
Katie Flynn, DVM
Katie.flynn@ky.gov(502) 782-5913
Deputy State Veterinarian
Kentucky Department of AgricultureFrankfort, Kentucky

2

I N T E R N AT I O N A L

103 were equine only premises and four cattle
premises. The Indiana serotype was involved in all
but seven premises in Texas where the New Jersey
serotype was implicated.

Second Quarter 2020

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Rebecca Ruby

Staff

Diane Furry
Tawana Brown
Dennis Duross

Correspondence should be
addressed to the editors,
Department of Veterinary
Science, Maxwell H. Gluck
Equine Research Center,
University of Kentucky,
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
Internet address:
http://gluck.ca.uky.edu/
equine-disease-quarterly
Material published in the
Quarterly is not subject tocopyright. Permission istherefore granted toreproduce articles, althoughacknowledgment of thesource and author is requested.
The University of Kentucky
is an Equal Opportunity
Organization.

Printed on recycled paper

he International Collating Centre, Newmarket, United Kingdom, and other sources
reported the following disease outbreaks.
The Republic of South Africa (RSA), theKingdom of Eswatini (SZ), and Thailand reported
outbreaks of African horse sickness (AHS). AHS
was confirmed in all nine provinces in the RSA,
with the majority of cases in Gauteng Province.
A single case was recorded in SZ. Outbreaks of
AHS continued in Thailand, with multiple cases
confirmed in 11 provinces.
Estonia, France, Germany, the Netherlands,
the UK, and the USA reported outbreaks ofequine influenza ranging from one (Estonia), two(Germany), three (UK), four (France and theNetherlands), to at least five in many states (USA),
where the disease is endemic. Although diagnosed
primarily in unvaccinated or partially vaccinatedhorses, isolated cases were also seen in vaccinatedanimals.
Strangles is considered endemic in most countries with outbreaks reported from Belgium (one),
France (seven), the Netherlands (16), Switzerland(four), and the USA (38 outbreaks in 17 states).
Equine herpesvirus 1 (EHV-1) related diseases
are believed endemic in most countries and wereconfirmed by Belgium, Canada, France, Germany,
Ireland, Japan, the Netherlands, the UK and theUSA. Respiratory disease outbreaks were recorded
by Belgium (two), France (two), Ireland (eight),
Japan (one), the Netherlands (one), the UK (two)and the USA (one). EHV-1 abortion was reported
by France (two outbreaks, single cases), Germany(one case), Japan (three outbreaks, one or twocases apiece), the Netherlands (two outbreaks,
one involving two cases and a case of neonatal
mortality, and another, a single case), the UK(three outbreaks, one involving multiple cases of
respiratory disease, one neonatal mortality andthree of neurologic disease; a second, involving
three cases of neonatal mortality; and a third, a caseof neonatal mortality). EHV-1 neurologic disease
was confirmed by Canada (three outbreaks, one
involved three cases; another, a single case; anda third, five cases with three having to be euthanized), and the USA (11 outbreaks in eight states,
the majority were single cases).

Numerous countries reported equine herpesvirus 4 (EHV-4) respiratory disease; outbreaks
ranged from one (Belgium, Switzerland), four
(Ireland), five (the Netherlands), to eight (France).
France also reported a case of EHV-4 abortion.
Single cases of equine infectious anemia wererecorded by Canada, Germany, and Hungary. The
USA recorded three outbreaks, each involved one
or two cases.
Equine piroplasmosis cases were reported by
the RSA (where the disease is endemic) and New
Zealand (a single case in an imported mare).
The USA recorded four cases of Tyzzer’s diseasecaused by Clostridium piliforme and also two casesof equine parvovirus associated hepatitis.
The UK detected Taylorella equigenitalis in an
imported stallion.
Equine coital exanthema (equine herpesvirus 3
infection) was diagnosed by France (one case) andthe USA (three cases).
Belgium reported a case of leptospiral abortionand two cases of abortion caused by Streptococcus
zooepidemicus.
Nocardioform placentitis/abortion was diagnosed by the USA, with 24 cases confirmed in
Kentucky and 27 in Pennsylvania. Amycolatopsis
spp. were implicated in the majority of cases.
The USA reported 13 cases of salmonellosis,
the majority involving Serogroup B isolates.
Rotavirus diarrhea in foals was diagnosed by
France (14 outbreaks, mostly single cases of infection) and the USA (78 cases, most involving 60-90
day old foals). A subset of 67 cases comprised 31of the G3 genotype, 21 of the G14 genotype and
15 involving both genotypes.
Clostridium perfringens was reported in 12 foals
and Clostridium difficile in seven foals by the USA.
The USA confirmed two fatal cases of Easternequine encephalomyelitis in Florida and two casesof West Nile encephalitis, one in California andthe other in Florida; one was euthanized.
A total of 71 cases of equine encephalosis wereconfirmed in seven provinces of the RSA.
The USA confirmed re-emergence of vesicularstomatitis in New Mexico in mid-April. The disease was subsequently confirmed in Arizona, Texas,
Kansas, and Nebraska. Of 107 affected premises,

Outbreaks of Rhodococcus equi associated diseases were reported by the USA. The number ofrecorded outbreaks is not considered reflective ofthe true incidence of the disease.

3

4

African Horse Sickness:
Potential Threat for Disease-free Countries

A

major outbreak of African horse sickness(AHS) in Thailand earlier this year was atimely reminder for animal health officials, veterinarians, and members of the horse industry of thevulnerability of equine populations to this disease.
Of all known equine infectious diseases, AHS is
the single most important in terms of devastating
losses in naïve horses and economic impact on international trade. It is a dreaded, non-contagious,
vector-borne disease with the potential to kill 50%
to 95% of affected horses.
The etiological agent of AHS is an RNA virus
belonging to the family Reoviridae, genus Orbivirus,
that is transmitted naturally by species of Culicoides
or midges. There are nine antigenically distinct serotypes of the virus. While the primary host species are
members of the family, Equidae, evidence of infection has also been found in African elephants, black
and white rhinoceroses, camels and dogs, none ofwhich are considered epidemiologically significant.
Historically, AHS was considered restricted totropical and subtropical regions of sub-SaharanAfrica, where it had been known to occur regularly for over 200 years. Although infrequent, thedisease has spread from west and north Africa tovarious southern European or Middle Easterncountries. The most significant such event occurred
between 1959 and 1963 when serotype 9 of AHS
virus spread out of Africa into and throughout the
Middle East, as far north as Turkey, and extended
as far east as Afghanistan, Pakistan, and India.
Concern over the risk that AHS poses for horseindustries in Europe has been keenly felt for sometime. Southern European countries are faced withthe potential threat of disease introduction from
migration of the virus northwards from regions in
Africa, where the disease is endemic. Spread of thevirus could result from the movement of nomads
and their animals, passive wind-borne carriage of
infected Culicoides over long distances, and legal
or illegal trade in zebra from countries where thedisease is currently active. A similar if not greaterrisk exists for the Middle East which experienced
incursions of AHS more frequently than any otherregion or country.

As the most recent occurrence of AHS in
Thailand has shown, distance is no guarantee ofsafety from the risk of introduction of this disease.
Thailand is approximately 6,000 miles distant from
where the virus responsible for this event probably
originated, and the furthest east in Asia where
AHS has ever been recorded. The most plausible
explanation as to the source of virus lies in the factthat a shipment of zebra arrived in Thailand three
to four weeks before the first AHS outbreak of thedisease was discovered. Zebra are considered thenatural reservoir of the virus, developing viremias
lasting up to 40 days.
This would not be the first occasion that importation of zebra from a country in which AHS
is a seasonal occurrence has been implicated in the
introduction of disease into a disease-free country.
A shipment of zebra was the confirmed source of
this virus for a major disease event that occurred in
Spain in 1987 and subsequently involved Portugal
and Morocco.
International trade in wildlife, both legal andillegal, is believed to have increased significantly
in recent years. What happened in the Iberian
Peninsula in 1987 and Thailand in 2020 highlights
the inherent risks of introducing a disease, such as
AHS, into previously disease-free countries.
The influence of climate change and global
warming on the epidemiology of AHS must also be
considered vis-à-vis the threat it poses for a diseasefree country. Increased ambient temperatures andreduced rainfall over a period of years has resulted
in more widespread geographic distribution ofsome of the major vectors of AHS, especially C.
imicola, in southern Europe. An increase in ambient temperature can influence not only the life
cycle of the Culicoides vector but also replicationof the virus in the vector. As temperatures rise, theinfection rate in Culicoides midges increases andtransmission of the virus can occur sooner, however
there is a concomitant decrease in the survival rateof the adult Culicoides. The overall result of thesechanges is a higher transmission rate of the virus
in a country possibly at risk of the introductionof AHS.

The occurrence in Thailand and the very recent
confirmation of AHS in Malaysia underscore theimportance of increasing awareness and familiarity with this dreaded disease among animal healthofficials, veterinarians and members of the equine
industry around the world. The potential consequences of AHS for the health of a country’s equine
population and economy highlight the need foran adequate level of national preparedness in a)minimizing the risk of introduction of this disease,b) maintaining a program of active surveillance
for the disease and c) having a response plan inplace in the remote event of the introduction of
the disease.
The take-home message from past and recent
occurrences of AHS is that there is no room forcomplacency over the potential threat it represents
for disease free-countries.
CONTACT:
Peter Timoney, MVB, MS, PhD, FRCVS
ptimoney@uky.edu(859) 218-1094
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky

N AT I O N A L

Consequences of Wildfires on the Health of Horses

W

Swelling of the supraorbital fossa, eyelids and facial tissues, and bilateral
tearing of a horse affected with the cardiac form of African horse sickness.
COURTESY DR. M. RODRIGUEZ

ildfires have become the new normal formany areas of the world, and subsequent
health consequences have emerged as an important problem affecting large numbers of horses.
For those of us in California with a Mediterranean
climate, large areas are affected by unrelenting
fires, which produce a particular challenge tohorse owners and those providing veterinary care.
There is a paucity of education and training indisaster and emergency response in veterinary
curricula, including the health consequences ofwildfires.
Wildfires can create health problems in horses
by direct and indirect exposure to flames andsmoke, injury during flight or evacuation, and/or
disruption of the horse’s food and water sources.
Wildfire-smoke health effects include primary
smoke exposure with direct smoke inhalation andsecondary smoke-related air quality issues in areas
adjacent to fires where smoke has permeated theenvironment. Wildfire smoke reduces air quality.
It contains small amounts of the toxic gases within
the smoke and particulate matter, soot, and othersubstances depending on what has burned. Particulate matter within smoke is microscopic andquickly descends into the lower airways of horses
producing bronchial and pulmonary inflammation. Eye and nasal irritation, coughing, andincreased respiratory efforts may be observed primarily in horses with a history of heaves or recurrent airway obstruction disorders. Published daily
reports of air quality indexes that guide humans
should be considered for determining horse-related
activities. Events that induce increased respiratory

efforts may need to be postponed, and horses withmassive smoke exposure may need four to six weeks
to recover completely from lower airway inflammation.
Horses with elevated respiratory rates or persistent cough may require veterinary intervention,
including bronchial dilators, airway hydration, andfurther testing. Smoke inhalation from immediate
association with fire can produce thermal injury
to the lungs from hot gases and the toxic effectsof the smoke components. Often these horses also
show evidence of thermal skin injuries.
Thermal injury burns to the skin, eyes, limbs,
and hoofs can be seen in horses exposed to excessive
heat and flames. Horses can incur first-, second-,
and third-degree burns. The extent of affected bodysurface area and the degree of burns can determine
prognosis. Equine burn victims may require daily
treatments lasting several weeks.
Flight-related injuries may be diverse and occur
when horses are fleeing the loud noises associatedwith rapidly approaching wildfires and related
responses of emergency personnel and fire suppression vehicles.
Horses left behind during evacuation may
remain uninjured by the fire. However, they canbe without food and water for extended periods,
because owners are often prevented from returning
to the affected area for several days.
Horses are frequently evacuated from areas at
risk. Evacuation carries many risks to horses associated with trailer loading mishaps and injuries,
exposure to infectious diseases due to housing
in new areas with high densities of horses, and2

I N T E R N AT I O N A L

103 were equine only premises and four cattle
premises. The Indiana serotype was involved in all
but seven premises in Texas where the New Jersey
serotype was implicated.

Second Quarter 2020

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Rebecca Ruby

Staff

Diane Furry
Tawana Brown
Dennis Duross

Correspondence should be
addressed to the editors,
Department of Veterinary
Science, Maxwell H. Gluck
Equine Research Center,
University of Kentucky,
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
Internet address:
http://gluck.ca.uky.edu/
equine-disease-quarterly
Material published in the
Quarterly is not subject tocopyright. Permission istherefore granted toreproduce articles, althoughacknowledgment of thesource and author is requested.
The University of Kentucky
is an Equal Opportunity
Organization.

Printed on recycled paper

he International Collating Centre, Newmarket, United Kingdom, and other sources
reported the following disease outbreaks.
The Republic of South Africa (RSA), theKingdom of Eswatini (SZ), and Thailand reported
outbreaks of African horse sickness (AHS). AHS
was confirmed in all nine provinces in the RSA,
with the majority of cases in Gauteng Province.
A single case was recorded in SZ. Outbreaks of
AHS continued in Thailand, with multiple cases
confirmed in 11 provinces.
Estonia, France, Germany, the Netherlands,
the UK, and the USA reported outbreaks ofequine influenza ranging from one (Estonia), two(Germany), three (UK), four (France and theNetherlands), to at least five in many states (USA),
where the disease is endemic. Although diagnosed
primarily in unvaccinated or partially vaccinatedhorses, isolated cases were also seen in vaccinatedanimals.
Strangles is considered endemic in most countries with outbreaks reported from Belgium (one),
France (seven), the Netherlands (16), Switzerland(four), and the USA (38 outbreaks in 17 states).
Equine herpesvirus 1 (EHV-1) related diseases
are believed endemic in most countries and wereconfirmed by Belgium, Canada, France, Germany,
Ireland, Japan, the Netherlands, the UK and theUSA. Respiratory disease outbreaks were recorded
by Belgium (two), France (two), Ireland (eight),
Japan (one), the Netherlands (one), the UK (two)and the USA (one). EHV-1 abortion was reported
by France (two outbreaks, single cases), Germany(one case), Japan (three outbreaks, one or twocases apiece), the Netherlands (two outbreaks,
one involving two cases and a case of neonatal
mortality, and another, a single case), the UK(three outbreaks, one involving multiple cases of
respiratory disease, one neonatal mortality andthree of neurologic disease; a second, involving
three cases of neonatal mortality; and a third, a caseof neonatal mortality). EHV-1 neurologic disease
was confirmed by Canada (three outbreaks, one
involved three cases; another, a single case; anda third, five cases with three having to be euthanized), and the USA (11 outbreaks in eight states,
the majority were single cases).

Numerous countries reported equine herpesvirus 4 (EHV-4) respiratory disease; outbreaks
ranged from one (Belgium, Switzerland), four
(Ireland), five (the Netherlands), to eight (France).
France also reported a case of EHV-4 abortion.
Single cases of equine infectious anemia wererecorded by Canada, Germany, and Hungary. The
USA recorded three outbreaks, each involved one
or two cases.
Equine piroplasmosis cases were reported by
the RSA (where the disease is endemic) and New
Zealand (a single case in an imported mare).
The USA recorded four cases of Tyzzer’s diseasecaused by Clostridium piliforme and also two casesof equine parvovirus associated hepatitis.
The UK detected Taylorella equigenitalis in an
imported stallion.
Equine coital exanthema (equine herpesvirus 3
infection) was diagnosed by France (one case) andthe USA (three cases).
Belgium reported a case of leptospiral abortionand two cases of abortion caused by Streptococcus
zooepidemicus.
Nocardioform placentitis/abortion was diagnosed by the USA, with 24 cases confirmed in
Kentucky and 27 in Pennsylvania. Amycolatopsis
spp. were implicated in the majority of cases.
The USA reported 13 cases of salmonellosis,
the majority involving Serogroup B isolates.
Rotavirus diarrhea in foals was diagnosed by
France (14 outbreaks, mostly single cases of infection) and the USA (78 cases, most involving 60-90
day old foals). A subset of 67 cases comprised 31of the G3 genotype, 21 of the G14 genotype and
15 involving both genotypes.
Clostridium perfringens was reported in 12 foals
and Clostridium difficile in seven foals by the USA.
The USA confirmed two fatal cases of Easternequine encephalomyelitis in Florida and two casesof West Nile encephalitis, one in California andthe other in Florida; one was euthanized.
A total of 71 cases of equine encephalosis wereconfirmed in seven provinces of the RSA.
The USA confirmed re-emergence of vesicularstomatitis in New Mexico in mid-April. The disease was subsequently confirmed in Arizona, Texas,
Kansas, and Nebraska. Of 107 affected premises,

Outbreaks of Rhodococcus equi associated diseases were reported by the USA. The number ofrecorded outbreaks is not considered reflective ofthe true incidence of the disease.

3

4

African Horse Sickness:
Potential Threat for Disease-free Countries

A

major outbreak of African horse sickness(AHS) in Thailand earlier this year was atimely reminder for animal health officials, veterinarians, and members of the horse industry of thevulnerability of equine populations to this disease.
Of all known equine infectious diseases, AHS is
the single most important in terms of devastating
losses in naïve horses and economic impact on international trade. It is a dreaded, non-contagious,
vector-borne disease with the potential to kill 50%
to 95% of affected horses.
The etiological agent of AHS is an RNA virus
belonging to the family Reoviridae, genus Orbivirus,
that is transmitted naturally by species of Culicoides
or midges. There are nine antigenically distinct serotypes of the virus. While the primary host species are
members of the family, Equidae, evidence of infection has also been found in African elephants, black
and white rhinoceroses, camels and dogs, none ofwhich are considered epidemiologically significant.
Historically, AHS was considered restricted totropical and subtropical regions of sub-SaharanAfrica, where it had been known to occur regularly for over 200 years. Although infrequent, thedisease has spread from west and north Africa tovarious southern European or Middle Easterncountries. The most significant such event occurred
between 1959 and 1963 when serotype 9 of AHS
virus spread out of Africa into and throughout the
Middle East, as far north as Turkey, and extended
as far east as Afghanistan, Pakistan, and India.
Concern over the risk that AHS poses for horseindustries in Europe has been keenly felt for sometime. Southern European countries are faced withthe potential threat of disease introduction from
migration of the virus northwards from regions in
Africa, where the disease is endemic. Spread of thevirus could result from the movement of nomads
and their animals, passive wind-borne carriage of
infected Culicoides over long distances, and legal
or illegal trade in zebra from countries where thedisease is currently active. A similar if not greaterrisk exists for the Middle East which experienced
incursions of AHS more frequently than any otherregion or country.

As the most recent occurrence of AHS in
Thailand has shown, distance is no guarantee ofsafety from the risk of introduction of this disease.
Thailand is approximately 6,000 miles distant from
where the virus responsible for this event probably
originated, and the furthest east in Asia where
AHS has ever been recorded. The most plausible
explanation as to the source of virus lies in the factthat a shipment of zebra arrived in Thailand three
to four weeks before the first AHS outbreak of thedisease was discovered. Zebra are considered thenatural reservoir of the virus, developing viremias
lasting up to 40 days.
This would not be the first occasion that importation of zebra from a country in which AHS
is a seasonal occurrence has been implicated in the
introduction of disease into a disease-free country.
A shipment of zebra was the confirmed source of
this virus for a major disease event that occurred in
Spain in 1987 and subsequently involved Portugal
and Morocco.
International trade in wildlife, both legal andillegal, is believed to have increased significantly
in recent years. What happened in the Iberian
Peninsula in 1987 and Thailand in 2020 highlights
the inherent risks of introducing a disease, such as
AHS, into previously disease-free countries.
The influence of climate change and global
warming on the epidemiology of AHS must also be
considered vis-à-vis the threat it poses for a diseasefree country. Increased ambient temperatures andreduced rainfall over a period of years has resulted
in more widespread geographic distribution ofsome of the major vectors of AHS, especially C.
imicola, in southern Europe. An increase in ambient temperature can influence not only the life
cycle of the Culicoides vector but also replicationof the virus in the vector. As temperatures rise, theinfection rate in Culicoides midges increases andtransmission of the virus can occur sooner, however
there is a concomitant decrease in the survival rateof the adult Culicoides. The overall result of thesechanges is a higher transmission rate of the virus
in a country possibly at risk of the introductionof AHS.

The occurrence in Thailand and the very recent
confirmation of AHS in Malaysia underscore theimportance of increasing awareness and familiarity with this dreaded disease among animal healthofficials, veterinarians and members of the equine
industry around the world. The potential consequences of AHS for the health of a country’s equine
population and economy highlight the need foran adequate level of national preparedness in a)minimizing the risk of introduction of this disease,b) maintaining a program of active surveillance
for the disease and c) having a response plan inplace in the remote event of the introduction of
the disease.
The take-home message from past and recent
occurrences of AHS is that there is no room forcomplacency over the potential threat it represents
for disease free-countries.
CONTACT:
Peter Timoney, MVB, MS, PhD, FRCVS
ptimoney@uky.edu(859) 218-1094
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky

N AT I O N A L

Consequences of Wildfires on the Health of Horses

W

Swelling of the supraorbital fossa, eyelids and facial tissues, and bilateral
tearing of a horse affected with the cardiac form of African horse sickness.
COURTESY DR. M. RODRIGUEZ

ildfires have become the new normal formany areas of the world, and subsequent
health consequences have emerged as an important problem affecting large numbers of horses.
For those of us in California with a Mediterranean
climate, large areas are affected by unrelenting
fires, which produce a particular challenge tohorse owners and those providing veterinary care.
There is a paucity of education and training indisaster and emergency response in veterinary
curricula, including the health consequences ofwildfires.
Wildfires can create health problems in horses
by direct and indirect exposure to flames andsmoke, injury during flight or evacuation, and/or
disruption of the horse’s food and water sources.
Wildfire-smoke health effects include primary
smoke exposure with direct smoke inhalation andsecondary smoke-related air quality issues in areas
adjacent to fires where smoke has permeated theenvironment. Wildfire smoke reduces air quality.
It contains small amounts of the toxic gases within
the smoke and particulate matter, soot, and othersubstances depending on what has burned. Particulate matter within smoke is microscopic andquickly descends into the lower airways of horses
producing bronchial and pulmonary inflammation. Eye and nasal irritation, coughing, andincreased respiratory efforts may be observed primarily in horses with a history of heaves or recurrent airway obstruction disorders. Published daily
reports of air quality indexes that guide humans
should be considered for determining horse-related
activities. Events that induce increased respiratory

efforts may need to be postponed, and horses withmassive smoke exposure may need four to six weeks
to recover completely from lower airway inflammation.
Horses with elevated respiratory rates or persistent cough may require veterinary intervention,
including bronchial dilators, airway hydration, andfurther testing. Smoke inhalation from immediate
association with fire can produce thermal injury
to the lungs from hot gases and the toxic effectsof the smoke components. Often these horses also
show evidence of thermal skin injuries.
Thermal injury burns to the skin, eyes, limbs,
and hoofs can be seen in horses exposed to excessive
heat and flames. Horses can incur first-, second-,
and third-degree burns. The extent of affected bodysurface area and the degree of burns can determine
prognosis. Equine burn victims may require daily
treatments lasting several weeks.
Flight-related injuries may be diverse and occur
when horses are fleeing the loud noises associatedwith rapidly approaching wildfires and related
responses of emergency personnel and fire suppression vehicles.
Horses left behind during evacuation may
remain uninjured by the fire. However, they canbe without food and water for extended periods,
because owners are often prevented from returning
to the affected area for several days.
Horses are frequently evacuated from areas at
risk. Evacuation carries many risks to horses associated with trailer loading mishaps and injuries,
exposure to infectious diseases due to housing
in new areas with high densities of horses, and2

I N T E R N AT I O N A L

103 were equine only premises and four cattle
premises. The Indiana serotype was involved in all
but seven premises in Texas where the New Jersey
serotype was implicated.

Second Quarter 2020

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Rebecca Ruby

Staff

Diane Furry
Tawana Brown
Dennis Duross

Correspondence should be
addressed to the editors,
Department of Veterinary
Science, Maxwell H. Gluck
Equine Research Center,
University of Kentucky,
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
Internet address:
http://gluck.ca.uky.edu/
equine-disease-quarterly
Material published in the
Quarterly is not subject tocopyright. Permission istherefore granted toreproduce articles, althoughacknowledgment of thesource and author is requested.
The University of Kentucky
is an Equal Opportunity
Organization.

Printed on recycled paper

he International Collating Centre, Newmarket, United Kingdom, and other sources
reported the following disease outbreaks.
The Republic of South Africa (RSA), theKingdom of Eswatini (SZ), and Thailand reported
outbreaks of African horse sickness (AHS). AHS
was confirmed in all nine provinces in the RSA,
with the majority of cases in Gauteng Province.
A single case was recorded in SZ. Outbreaks of
AHS continued in Thailand, with multiple cases
confirmed in 11 provinces.
Estonia, France, Germany, the Netherlands,
the UK, and the USA reported outbreaks ofequine influenza ranging from one (Estonia), two(Germany), three (UK), four (France and theNetherlands), to at least five in many states (USA),
where the disease is endemic. Although diagnosed
primarily in unvaccinated or partially vaccinatedhorses, isolated cases were also seen in vaccinatedanimals.
Strangles is considered endemic in most countries with outbreaks reported from Belgium (one),
France (seven), the Netherlands (16), Switzerland(four), and the USA (38 outbreaks in 17 states).
Equine herpesvirus 1 (EHV-1) related diseases
are believed endemic in most countries and wereconfirmed by Belgium, Canada, France, Germany,
Ireland, Japan, the Netherlands, the UK and theUSA. Respiratory disease outbreaks were recorded
by Belgium (two), France (two), Ireland (eight),
Japan (one), the Netherlands (one), the UK (two)and the USA (one). EHV-1 abortion was reported
by France (two outbreaks, single cases), Germany(one case), Japan (three outbreaks, one or twocases apiece), the Netherlands (two outbreaks,
one involving two cases and a case of neonatal
mortality, and another, a single case), the UK(three outbreaks, one involving multiple cases of
respiratory disease, one neonatal mortality andthree of neurologic disease; a second, involving
three cases of neonatal mortality; and a third, a caseof neonatal mortality). EHV-1 neurologic disease
was confirmed by Canada (three outbreaks, one
involved three cases; another, a single case; anda third, five cases with three having to be euthanized), and the USA (11 outbreaks in eight states,
the majority were single cases).

Numerous countries reported equine herpesvirus 4 (EHV-4) respiratory disease; outbreaks
ranged from one (Belgium, Switzerland), four
(Ireland), five (the Netherlands), to eight (France).
France also reported a case of EHV-4 abortion.
Single cases of equine infectious anemia wererecorded by Canada, Germany, and Hungary. The
USA recorded three outbreaks, each involved one
or two cases.
Equine piroplasmosis cases were reported by
the RSA (where the disease is endemic) and New
Zealand (a single case in an imported mare).
The USA recorded four cases of Tyzzer’s diseasecaused by Clostridium piliforme and also two casesof equine parvovirus associated hepatitis.
The UK detected Taylorella equigenitalis in an
imported stallion.
Equine coital exanthema (equine herpesvirus 3
infection) was diagnosed by France (one case) andthe USA (three cases).
Belgium reported a case of leptospiral abortionand two cases of abortion caused by Streptococcus
zooepidemicus.
Nocardioform placentitis/abortion was diagnosed by the USA, with 24 cases confirmed in
Kentucky and 27 in Pennsylvania. Amycolatopsis
spp. were implicated in the majority of cases.
The USA reported 13 cases of salmonellosis,
the majority involving Serogroup B isolates.
Rotavirus diarrhea in foals was diagnosed by
France (14 outbreaks, mostly single cases of infection) and the USA (78 cases, most involving 60-90
day old foals). A subset of 67 cases comprised 31of the G3 genotype, 21 of the G14 genotype and
15 involving both genotypes.
Clostridium perfringens was reported in 12 foals
and Clostridium difficile in seven foals by the USA.
The USA confirmed two fatal cases of Easternequine encephalomyelitis in Florida and two casesof West Nile encephalitis, one in California andthe other in Florida; one was euthanized.
A total of 71 cases of equine encephalosis wereconfirmed in seven provinces of the RSA.
The USA confirmed re-emergence of vesicularstomatitis in New Mexico in mid-April. The disease was subsequently confirmed in Arizona, Texas,
Kansas, and Nebraska. Of 107 affected premises,

Outbreaks of Rhodococcus equi associated diseases were reported by the USA. The number ofrecorded outbreaks is not considered reflective ofthe true incidence of the disease.

3

4

African Horse Sickness:
Potential Threat for Disease-free Countries

A

major outbreak of African horse sickness(AHS) in Thailand earlier this year was atimely reminder for animal health officials, veterinarians, and members of the horse industry of thevulnerability of equine populations to this disease.
Of all known equine infectious diseases, AHS is
the single most important in terms of devastating
losses in naïve horses and economic impact on international trade. It is a dreaded, non-contagious,
vector-borne disease with the potential to kill 50%
to 95% of affected horses.
The etiological agent of AHS is an RNA virus
belonging to the family Reoviridae, genus Orbivirus,
that is transmitted naturally by species of Culicoides
or midges. There are nine antigenically distinct serotypes of the virus. While the primary host species are
members of the family, Equidae, evidence of infection has also been found in African elephants, black
and white rhinoceroses, camels and dogs, none ofwhich are considered epidemiologically significant.
Historically, AHS was considered restricted totropical and subtropical regions of sub-SaharanAfrica, where it had been known to occur regularly for over 200 years. Although infrequent, thedisease has spread from west and north Africa tovarious southern European or Middle Easterncountries. The most significant such event occurred
between 1959 and 1963 when serotype 9 of AHS
virus spread out of Africa into and throughout the
Middle East, as far north as Turkey, and extended
as far east as Afghanistan, Pakistan, and India.
Concern over the risk that AHS poses for horseindustries in Europe has been keenly felt for sometime. Southern European countries are faced withthe potential threat of disease introduction from
migration of the virus northwards from regions in
Africa, where the disease is endemic. Spread of thevirus could result from the movement of nomads
and their animals, passive wind-borne carriage of
infected Culicoides over long distances, and legal
or illegal trade in zebra from countries where thedisease is currently active. A similar if not greaterrisk exists for the Middle East which experienced
incursions of AHS more frequently than any otherregion or country.

As the most recent occurrence of AHS in
Thailand has shown, distance is no guarantee ofsafety from the risk of introduction of this disease.
Thailand is approximately 6,000 miles distant from
where the virus responsible for this event probably
originated, and the furthest east in Asia where
AHS has ever been recorded. The most plausible
explanation as to the source of virus lies in the factthat a shipment of zebra arrived in Thailand three
to four weeks before the first AHS outbreak of thedisease was discovered. Zebra are considered thenatural reservoir of the virus, developing viremias
lasting up to 40 days.
This would not be the first occasion that importation of zebra from a country in which AHS
is a seasonal occurrence has been implicated in the
introduction of disease into a disease-free country.
A shipment of zebra was the confirmed source of
this virus for a major disease event that occurred in
Spain in 1987 and subsequently involved Portugal
and Morocco.
International trade in wildlife, both legal andillegal, is believed to have increased significantly
in recent years. What happened in the Iberian
Peninsula in 1987 and Thailand in 2020 highlights
the inherent risks of introducing a disease, such as
AHS, into previously disease-free countries.
The influence of climate change and global
warming on the epidemiology of AHS must also be
considered vis-à-vis the threat it poses for a diseasefree country. Increased ambient temperatures andreduced rainfall over a period of years has resulted
in more widespread geographic distribution ofsome of the major vectors of AHS, especially C.
imicola, in southern Europe. An increase in ambient temperature can influence not only the life
cycle of the Culicoides vector but also replicationof the virus in the vector. As temperatures rise, theinfection rate in Culicoides midges increases andtransmission of the virus can occur sooner, however
there is a concomitant decrease in the survival rateof the adult Culicoides. The overall result of thesechanges is a higher transmission rate of the virus
in a country possibly at risk of the introductionof AHS.

The occurrence in Thailand and the very recent
confirmation of AHS in Malaysia underscore theimportance of increasing awareness and familiarity with this dreaded disease among animal healthofficials, veterinarians and members of the equine
industry around the world. The potential consequences of AHS for the health of a country’s equine
population and economy highlight the need foran adequate level of national preparedness in a)minimizing the risk of introduction of this disease,b) maintaining a program of active surveillance
for the disease and c) having a response plan inplace in the remote event of the introduction of
the disease.
The take-home message from past and recent
occurrences of AHS is that there is no room forcomplacency over the potential threat it represents
for disease free-countries.
CONTACT:
Peter Timoney, MVB, MS, PhD, FRCVS
ptimoney@uky.edu(859) 218-1094
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky

N AT I O N A L

Consequences of Wildfires on the Health of Horses

W

Swelling of the supraorbital fossa, eyelids and facial tissues, and bilateral
tearing of a horse affected with the cardiac form of African horse sickness.
COURTESY DR. M. RODRIGUEZ

ildfires have become the new normal formany areas of the world, and subsequent
health consequences have emerged as an important problem affecting large numbers of horses.
For those of us in California with a Mediterranean
climate, large areas are affected by unrelenting
fires, which produce a particular challenge tohorse owners and those providing veterinary care.
There is a paucity of education and training indisaster and emergency response in veterinary
curricula, including the health consequences ofwildfires.
Wildfires can create health problems in horses
by direct and indirect exposure to flames andsmoke, injury during flight or evacuation, and/or
disruption of the horse’s food and water sources.
Wildfire-smoke health effects include primary
smoke exposure with direct smoke inhalation andsecondary smoke-related air quality issues in areas
adjacent to fires where smoke has permeated theenvironment. Wildfire smoke reduces air quality.
It contains small amounts of the toxic gases within
the smoke and particulate matter, soot, and othersubstances depending on what has burned. Particulate matter within smoke is microscopic andquickly descends into the lower airways of horses
producing bronchial and pulmonary inflammation. Eye and nasal irritation, coughing, andincreased respiratory efforts may be observed primarily in horses with a history of heaves or recurrent airway obstruction disorders. Published daily
reports of air quality indexes that guide humans
should be considered for determining horse-related
activities. Events that induce increased respiratory

efforts may need to be postponed, and horses withmassive smoke exposure may need four to six weeks
to recover completely from lower airway inflammation.
Horses with elevated respiratory rates or persistent cough may require veterinary intervention,
including bronchial dilators, airway hydration, andfurther testing. Smoke inhalation from immediate
association with fire can produce thermal injury
to the lungs from hot gases and the toxic effectsof the smoke components. Often these horses also
show evidence of thermal skin injuries.
Thermal injury burns to the skin, eyes, limbs,
and hoofs can be seen in horses exposed to excessive
heat and flames. Horses can incur first-, second-,
and third-degree burns. The extent of affected bodysurface area and the degree of burns can determine
prognosis. Equine burn victims may require daily
treatments lasting several weeks.
Flight-related injuries may be diverse and occur
when horses are fleeing the loud noises associatedwith rapidly approaching wildfires and related
responses of emergency personnel and fire suppression vehicles.
Horses left behind during evacuation may
remain uninjured by the fire. However, they canbe without food and water for extended periods,
because owners are often prevented from returning
to the affected area for several days.
Horses are frequently evacuated from areas at
risk. Evacuation carries many risks to horses associated with trailer loading mishaps and injuries,
exposure to infectious diseases due to housing
in new areas with high densities of horses, andEquine Disease Quarterly Newsletter

5poor biosecurity. Many evacuations must occur
rapidly and at night, which produces additionalrisks. Early evacuation is strongly suggested using
a previously prepared plan that addresses capture,
movement to a safe area, and horse identification.

CONTACT:John Madigan, DVM, MS Diplomate ACVIM, ACAW,Distinguished Professor-Emeritus
jemadigan@ucdavis.edu
530-304-1212
University of California-Davis
Davis, California

Presorted Standard
US Postage Paid
Permit 51
Lexington KY

Department of Veterinary Science
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky 40546-0099
Address Service Requested

F U N D E D B Y U N D E R W R I T E R S AT L LOY D ' S , LO N D O N

KENTUCKYOCTOBER 2020
Volume 29, Number 4

Rhodococcus Equi-associated Extra-pulmonary DisordersRhodococcus equi is a ubiquitous environmental bacterium that causes one of the costliest
diseases on equine breeding farms. The most common disease manifestation is pneumonia in young
foals. Infection with R. equi appears to occur inthe first few days of life and remains subclinicalfor several weeks. Many foals eliminate infection
on their own, while others develop respiratory
disease. Management of rhodococcosis can befurther complicated by the development of extrapulmonary disorders (EPDs).
Extra-pulmonary disorders refer to any clinical manifestation of rhodococcosis other thanpneumonia. A large study estimated that 74% of
infected foals had at least one EPD. In many cases,
EPDs were not diagnosed until postmortem examination. In this study, survival was significantly
lower in foals with EPDs. Factors that influence
development of EPDs are not completely understood, but it is generally accepted that EPDs areindicative of a more severe infection. EPDs canpose a major diagnostic challenge and warrant
thorough evaluation of any sick juvenile foal.
Identification of EPDs can aid in selection of appropriate therapy, monitoring response to therapy,
and prognostication.
Clinical signs of R. equi pneumonia rarely develop before three to four weeks of age. While bloodwork and ultrasonography can increase suspicion
of infection, a tracheal wash provides a definitive
diagnosis. Suspicion of R. equi pneumonia should
prompt investigation for EPDs elsewhere in thebody.
Intra-abdominal abscessation is one of the mostcommon EPD. It is suspected that R. equi spreads
hematogenously or is ingested in sputum to cause
abdominal lesions. Abscesses are best diagnosed via
ultrasonography, highlighting the importance ofabdominal ultrasonography in foals with pneumonia. Alternatively, abdominal abscessation might
only manifest as a recurrent fever or unexplained

high white blood cell count. Generally, a sample
cannot be obtained from abscesses to confirm R.
equi involvement. Presumptive diagnosis is madebased on the foal’s age and concurrent pneumonia.
Successful treatment of abscessation is possible,
but foals with intra-abdominal abscesses are ata significantly greater mortality risk. Survivability seems to decrease with increasing size ofabdominal abscesses. Treatment of abdominal R.
equi infection includes provision of a long courseof antimicrobials. Surgical debulking or resection
typically is not possible due to attachments of theabscess to adjacent structures.
R. equi can spread hematogenously and resultin osteomyelitis. Clinical signs of affected foals include lameness, ataxia, and recumbency. Retrieving
diagnostic samples from affected sites for diseaseconfirmation can be difficult. Osteomyelitis may
be best diagnosed via radiography or computed tomography. Successful treatment has been reported,but prognosis is typically considered poor. Other
documented sites of R. equi infection include thecentral nervous system, kidney, and liver.
Polysynovitis is perhaps the most commonly
observed EPD. It is characterized by symmetricjoint effusion without lameness. R. equi is rarely
cultured from affected joints; this finding has longsupported a conclusion that this phenomenon isimmune-mediated. Recently, experimental infection of foals resulted in the isolation of R. equi fromsynovial fluid 14 days post-infection. This lends
support to a newer theory that polysynovitis isa septic complication of infection that might
actually result from hematogenous spread. In thesame study, experimental infection also resulted
in the isolation of R. equi from ocular fluid. Uveitis has also been considered immune-mediated.
Unlike polysynovitis, R. equi uveitis is strongly
associated with nonsurvival in foals. With both ofthese EPDs, a suspected hematogenous origin is
an interesting development in our understanding

C O M M E N TA RY
IN THIS ISSUEof the disease as many other EPDs appear to precipitate from bacteremia. The role of the immune
response in the development of EPDs should not
be discounted yet, as several reports exist of foals
affected by immune-mediated hemolytic anemia
associated with R. equi infection.
Extra-pulmonary disorders are frequently
encountered during the management of foals
infected with Rhodococcus equi. As current litera-ture suggests a septic process in the pathogenesisof polysynovitis and uveitis, it is logical to speculatethat the precipitation of most EPDs is a functionof bacteremia and the host’s immune response tosystemic infection.
CONTACT:
William Gilsenan, VMD, Dipl. ACVIM-LAIM(859) 233-0371
Rood and Riddle Equine Hospital
Lexington, KentuckyT

he COVID-19 pandemic has heightened theawareness of the horse industry regarding
Commentary
the potential introduction and spread of foreign
animal diseases (FAD). The human pandemic
International
highlights the importance of early detection,
Second Quarterlaboratory utilization of high capacity, validated
2020  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2diagnostic testing, and coordinated implementaAfrican Horsetion of a disease response plan. How would the
Sickness .  .  .  .  .  .  .  .  .  .  .  .  . 3national and international community respond toa pandemic of equine infectious disease?
National
The threat of an FAD entering the U.S. is a
Wildfires .  .  .  .  .  .  .  .  .  .  .  .  . 4 top concern of regulatory animal health officials.
These officials are responsible for implementing
Kentucky
mitigation measures to prevent introduction of a
Rhodococcus equi .  .  .  . 5 highly contagious or vector-borne disease agent.
Risk reduction includes pre-import testing andpost-import quarantine as well as testing of live
animals and animal products to ensure that diseases
with the potential to become widely disseminated
do not enter the country. FAD may be introduced
by an asymptomatic carrier, contaminated equipment, or an infected vector or reservoir host.
Should an FAD enter the country, private practitioners and equine owners would provide criticalsurveillance and hopefully its early detection. Any
individual suspecting an FAD should immediately
report the case to a local regulatory authority.
Once reported, an FAD diagnostician will visit
the premises within 24 hours of notification to
perform an onsite investigation, examine affected
College of Agriculture, animals, obtain appropriate samples for laboratory
Food and Environment testing, quarantine the animals and/or premises,
Department ofand implement disease control measures. If diVeterinary Scienceagnostic testing at the Foreign Animal Disease
Laboratory on Plum Island, NY, confirms an FAD,
then regulatory officials will implement movement
restrictions and disease eradication measures.
Unlike an outbreak of an endemic disease,
Lloyd’s—An internationalsuch as strangles or equine influenza, all members
insurance market forof the equine industry across the country would
bloodstock and otherspecialist insurance.

be impacted by an FAD outbreak. Confirmationof an FAD results in activation of a national response plan with coordination of state and federal
animal health officials. With detection of an FAD,
countries can prohibit entry of equids from the affected country and domestic movement of horses
is restricted. Restrictions may extend to equine
affiliated entities such as nutritionists, farriers,
equine dentists, and feed and hay suppliers.
The ultimate outcome following the introduction of an FAD depends on the response of regulatory officials in concert with the equine industry.
Preparedness, prompt response, and collaboration
are key to success. Unfortunately, domestic equinedisease outbreaks in recent years have shown theequine industry is underprepared due mainly tolimited implementation of biosecurity measuresand insufficient use of diagnostic testing. Furthermore, limited resources at national and local levels
to address equine disease issues result in the inability
to focus on the development and training involvedin a national equine FAD response plan. Lastly,
segmentation of different sectors of the equine
industry leads to challenges in communication andcollaboration and slows the response to an FAD.
The equine industry has a unique opportunity
to learn from the current human pandemic andenhance equine FAD preparedness and response.
Equine stakeholders can reach out to local andnational regulatory authorities to prioritize the development of an equine FAD response plan, which
focuses on business continuity while protecting thehealth of the nation’s equine population.
CONTACT:
Katie Flynn, DVM
Katie.flynn@ky.gov(502) 782-5913
Deputy State Veterinarian
Kentucky Department of AgricultureFrankfort, Kentucky

Equine Disease Quarterly Newsletter

5poor biosecurity. Many evacuations must occur
rapidly and at night, which produces additionalrisks. Early evacuation is strongly suggested using
a previously prepared plan that addresses capture,
movement to a safe area, and horse identification.

CONTACT:John Madigan, DVM, MS Diplomate ACVIM, ACAW,Distinguished Professor-Emeritus
jemadigan@ucdavis.edu
530-304-1212
University of California-Davis
Davis, California

Department of Veterinary Science
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky 40546-0099
Address Service Requested

F U N D E D B Y U N D E R W R I T E R S AT L LOY D ' S , LO N D O N

KENTUCKYOCTOBER 2020
Volume 29, Number 4

Rhodococcus Equi-associated Extra-pulmonary DisordersRhodococcus equi is a ubiquitous environmental bacterium that causes one of the costliest
diseases on equine breeding farms. The most common disease manifestation is pneumonia in young
foals. Infection with R. equi appears to occur inthe first few days of life and remains subclinicalfor several weeks. Many foals eliminate infection
on their own, while others develop respiratory
disease. Management of rhodococcosis can befurther complicated by the development of extrapulmonary disorders (EPDs).
Extra-pulmonary disorders refer to any clinical manifestation of rhodococcosis other thanpneumonia. A large study estimated that 74% of
infected foals had at least one EPD. In many cases,
EPDs were not diagnosed until postmortem examination. In this study, survival was significantly
lower in foals with EPDs. Factors that influence
development of EPDs are not completely understood, but it is generally accepted that EPDs areindicative of a more severe infection. EPDs canpose a major diagnostic challenge and warrant
thorough evaluation of any sick juvenile foal.
Identification of EPDs can aid in selection of appropriate therapy, monitoring response to therapy,
and prognostication.
Clinical signs of R. equi pneumonia rarely develop before three to four weeks of age. While bloodwork and ultrasonography can increase suspicion
of infection, a tracheal wash provides a definitive
diagnosis. Suspicion of R. equi pneumonia should
prompt investigation for EPDs elsewhere in thebody.
Intra-abdominal abscessation is one of the mostcommon EPD. It is suspected that R. equi spreads
hematogenously or is ingested in sputum to cause
abdominal lesions. Abscesses are best diagnosed via
ultrasonography, highlighting the importance ofabdominal ultrasonography in foals with pneumonia. Alternatively, abdominal abscessation might
only manifest as a recurrent fever or unexplained

high white blood cell count. Generally, a sample
cannot be obtained from abscesses to confirm R.
equi involvement. Presumptive diagnosis is madebased on the foal’s age and concurrent pneumonia.
Successful treatment of abscessation is possible,
but foals with intra-abdominal abscesses are ata significantly greater mortality risk. Survivability seems to decrease with increasing size ofabdominal abscesses. Treatment of abdominal R.
equi infection includes provision of a long courseof antimicrobials. Surgical debulking or resection
typically is not possible due to attachments of theabscess to adjacent structures.
R. equi can spread hematogenously and resultin osteomyelitis. Clinical signs of affected foals include lameness, ataxia, and recumbency. Retrieving
diagnostic samples from affected sites for diseaseconfirmation can be difficult. Osteomyelitis may
be best diagnosed via radiography or computed tomography. Successful treatment has been reported,but prognosis is typically considered poor. Other
documented sites of R. equi infection include thecentral nervous system, kidney, and liver.
Polysynovitis is perhaps the most commonly
observed EPD. It is characterized by symmetricjoint effusion without lameness. R. equi is rarely
cultured from affected joints; this finding has longsupported a conclusion that this phenomenon isimmune-mediated. Recently, experimental infection of foals resulted in the isolation of R. equi fromsynovial fluid 14 days post-infection. This lends
support to a newer theory that polysynovitis isa septic complication of infection that might
actually result from hematogenous spread. In thesame study, experimental infection also resulted
in the isolation of R. equi from ocular fluid. Uveitis has also been considered immune-mediated.
Unlike polysynovitis, R. equi uveitis is strongly
associated with nonsurvival in foals. With both ofthese EPDs, a suspected hematogenous origin is
an interesting development in our understanding

C O M M E N TA RY
IN THIS ISSUEof the disease as many other EPDs appear to precipitate from bacteremia. The role of the immune
response in the development of EPDs should not
be discounted yet, as several reports exist of foals
affected by immune-mediated hemolytic anemia
associated with R. equi infection.
Extra-pulmonary disorders are frequently
encountered during the management of foals
infected with Rhodococcus equi. As current litera-ture suggests a septic process in the pathogenesisof polysynovitis and uveitis, it is logical to speculatethat the precipitation of most EPDs is a functionof bacteremia and the host’s immune response tosystemic infection.
CONTACT:
William Gilsenan, VMD, Dipl. ACVIM-LAIM(859) 233-0371
Rood and Riddle Equine Hospital
Lexington, KentuckyT

he COVID-19 pandemic has heightened theawareness of the horse industry regarding
Commentary
the potential introduction and spread of foreign
animal diseases (FAD). The human pandemic
International
highlights the importance of early detection,
Second Quarterlaboratory utilization of high capacity, validated
2020  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2diagnostic testing, and coordinated implementaAfrican Horsetion of a disease response plan. How would the
Sickness .  .  .  .  .  .  .  .  .  .  .  .  . 3national and international community respond toa pandemic of equine infectious disease?
National
The threat of an FAD entering the U.S. is a
Wildfires .  .  .  .  .  .  .  .  .  .  .  .  . 4 top concern of regulatory animal health officials.
These officials are responsible for implementing
Kentucky
mitigation measures to prevent introduction of a
Rhodococcus equi  .  .  . 5 highly contagious or vector-borne disease agent.
Risk reduction includes pre-import testing andpost-import quarantine as well as testing of live
animals and animal products to ensure that diseases
with the potential to become widely disseminated
do not enter the country. FAD may be introduced
by an asymptomatic carrier, contaminated equipment, or an infected vector or reservoir host.
Should an FAD enter the country, private practitioners and equine owners would provide criticalsurveillance and hopefully its early detection. Any
individual suspecting an FAD should immediately
report the case to a local regulatory authority.
Once reported, an FAD diagnostician will visit
the premises within 24 hours of notification to
perform an onsite investigation, examine affected
College of Agriculture, animals, obtain appropriate samples for laboratory
Food and Environment testing, quarantine the animals and/or premises,
Department ofand implement disease control measures. If diVeterinary Scienceagnostic testing at the Foreign Animal Disease
Laboratory on Plum Island, NY, confirms an FAD,
then regulatory officials will implement movement
restrictions and disease eradication measures.
Unlike an outbreak of an endemic disease,
Lloyd’s—An internationalsuch as strangles or equine influenza, all members
insurance market forof the equine industry across the country would
bloodstock and otherspecialist insurance.

be impacted by an FAD outbreak. Confirmationof an FAD results in activation of a national response plan with coordination of state and federal
animal health officials. With detection of an FAD,
countries can prohibit entry of equids from the affected country and domestic movement of horses
is restricted. Restrictions may extend to equine
affiliated entities such as nutritionists, farriers,
equine dentists, and feed and hay suppliers.
The ultimate outcome following the introduction of an FAD depends on the response of regulatory officials in concert with the equine industry.
Preparedness, prompt response, and collaboration
are key to success. Unfortunately, domestic equinedisease outbreaks in recent years have shown theequine industry is underprepared due mainly tolimited implementation of biosecurity measuresand insufficient use of diagnostic testing. Furthermore, limited resources at national and local levels
to address equine disease issues result in the inability
to focus on the development and training involvedin a national equine FAD response plan. Lastly,
segmentation of different sectors of the equine
industry leads to challenges in communication andcollaboration and slows the response to an FAD.
The equine industry has a unique opportunity
to learn from the current human pandemic andenhance equine FAD preparedness and response.
Equine stakeholders can reach out to local andnational regulatory authorities to prioritize the development of an equine FAD response plan, which
focuses on business continuity while protecting thehealth of the nation’s equine population.
CONTACT:
Katie Flynn, DVM
Katie.flynn@ky.gov(502) 782-5913
Deputy State Veterinarian
Kentucky Department of AgricultureFrankfort, Kentucky

2

I N T E R N AT I O N A L

103 were equine only premises and four cattle
premises. The Indiana serotype was involved in all
but seven premises in Texas where the New Jersey
serotype was implicated.

Second Quarter 2020

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Rebecca Ruby

Staff

Diane Furry
Tawana Brown
Dennis Duross

Correspondence should be
addressed to the editors,
Department of Veterinary
Science, Maxwell H. Gluck
Equine Research Center,
University of Kentucky,
Lexington, Kentucky USA,40546-0099
Telephone (859) 257-4757
Fax (859) 257-8542
Internet address:
http://gluck.ca.uky.edu/
equine-disease-quarterly
Material published in the
Quarterly is not subject tocopyright. Permission istherefore granted toreproduce articles, althoughacknowledgment of thesource and author is requested.
The University of Kentucky
is an Equal Opportunity
Organization.

Printed on recycled paper

he International Collating Centre, Newmarket, United Kingdom, and other sources
reported the following disease outbreaks.
The Republic of South Africa (RSA), theKingdom of Eswatini (SZ), and Thailand reported
outbreaks of African horse sickness (AHS). AHS
was confirmed in all nine provinces in the RSA,
with the majority of cases in Gauteng Province.
A single case was recorded in SZ. Outbreaks of
AHS continued in Thailand, with multiple cases
confirmed in 11 provinces.
Estonia, France, Germany, the Netherlands,
the UK, and the USA reported outbreaks ofequine influenza ranging from one (Estonia), two(Germany), three (UK), four (France and theNetherlands), to at least five in many states (USA),
where the disease is endemic. Although diagnosed
primarily in unvaccinated or partially vaccinatedhorses, isolated cases were also seen in vaccinatedanimals.
Strangles is considered endemic in most countries with outbreaks reported from Belgium (one),
France (seven), the Netherlands (16), Switzerland(four), and the USA (38 outbreaks in 17 states).
Equine herpesvirus 1 (EHV-1) related diseases
are believed endemic in most countries and wereconfirmed by Belgium, Canada, France, Germany,
Ireland, Japan, the Netherlands, the UK and theUSA. Respiratory disease outbreaks were recorded
by Belgium (two), France (two), Ireland (eight),
Japan (one), the Netherlands (one), the UK (two)and the USA (one). EHV-1 abortion was reported
by France (two outbreaks, single cases), Germany(one case), Japan (three outbreaks, one or twocases apiece), the Netherlands (two outbreaks,
one involving two cases and a case of neonatal
mortality, and another, a single case), the UK(three outbreaks, one involving multiple cases of
respiratory disease, one neonatal mortality andthree of neurologic disease; a second, involving
three cases of neonatal mortality; and a third, a caseof neonatal mortality). EHV-1 neurologic disease
was confirmed by Canada (three outbreaks, one
involved three cases; another, a single case; anda third, five cases with three having to be euthanized), and the USA (11 outbreaks in eight states,
the majority were single cases).

Numerous countries reported equine herpesvirus 4 (EHV-4) respiratory disease; outbreaks
ranged from one (Belgium, Switzerland), four
(Ireland), five (the Netherlands), to eight (France).
France also reported a case of EHV-4 abortion.
Single cases of equine infectious anemia wererecorded by Canada, Germany, and Hungary. The
USA recorded three outbreaks, each involved one
or two cases.
Equine piroplasmosis cases were reported by
the RSA (where the disease is endemic) and New
Zealand (a single case in an imported mare).
The USA recorded four cases of Tyzzer’s diseasecaused by Clostridium piliforme and also two casesof equine parvovirus associated hepatitis.
The UK detected Taylorella equigenitalis in an
imported stallion.
Equine coital exanthema (equine herpesvirus 3
infection) was diagnosed by France (one case) andthe USA (three cases).
Belgium reported a case of leptospiral abortionand two cases of abortion caused by Streptococcus
zooepidemicus.
Nocardioform placentitis/abortion was diagnosed by the USA, with 24 cases confirmed in
Kentucky and 27 in Pennsylvania. Amycolatopsis
spp. were implicated in the majority of cases.
The USA reported 13 cases of salmonellosis,
the majority involving Serogroup B isolates.
Rotavirus diarrhea in foals was diagnosed by
France (14 outbreaks, mostly single cases of infection) and the USA (78 cases, most involving 60-90
day old foals). A subset of 67 cases comprised 31of the G3 genotype, 21 of the G14 genotype and
15 involving both genotypes.
Clostridium perfringens was reported in 12 foals
and Clostridium difficile in seven foals by the USA.
The USA confirmed two fatal cases of Easternequine encephalomyelitis in Florida and two casesof West Nile encephalitis, one in California andthe other in Florida; one was euthanized.
A total of 71 cases of equine encephalosis wereconfirmed in seven provinces of the RSA.
The USA confirmed re-emergence of vesicularstomatitis in New Mexico in mid-April. The disease was subsequently confirmed in Arizona, Texas,
Kansas, and Nebraska. Of 107 affected premises,

Outbreaks of Rhodococcus equi associated diseases were reported by the USA. The number ofrecorded outbreaks is not considered reflective ofthe true incidence of the disease.

3

4

African Horse Sickness:
Potential Threat for Disease-free Countries

A

major outbreak of African horse sickness(AHS) in Thailand earlier this year was atimely reminder for animal health officials, veterinarians, and members of the horse industry of thevulnerability of equine populations to this disease.
Of all known equine infectious diseases, AHS is
the single most important in terms of devastating
losses in naïve horses and economic impact on international trade. It is a dreaded, non-contagious,
vector-borne disease with the potential to kill 50%
to 95% of affected horses.
The etiological agent of AHS is an RNA virus
belonging to the family Reoviridae, genus Orbivirus,
that is transmitted naturally by species of Culicoides
or midges. There are nine antigenically distinct serotypes of the virus. While the primary host species are
members of the family, Equidae, evidence of infection has also been found in African elephants, black
and white rhinoceroses, camels and dogs, none ofwhich are considered epidemiologically significant.
Historically, AHS was considered restricted totropical and subtropical regions of sub-SaharanAfrica, where it had been known to occur regularly for over 200 years. Although infrequent, thedisease has spread from west and north Africa tovarious southern European or Middle Easterncountries. The most significant such event occurred
between 1959 and 1963 when serotype 9 of AHS
virus spread out of Africa into and throughout the
Middle East, as far north as Turkey, and extended
as far east as Afghanistan, Pakistan, and India.
Concern over the risk that AHS poses for horseindustries in Europe has been keenly felt for sometime. Southern European countries are faced withthe potential threat of disease introduction from
migration of the virus northwards from regions in
Africa, where the disease is endemic. Spread of thevirus could result from the movement of nomads
and their animals, passive wind-borne carriage of
infected Culicoides over long distances, and legal
or illegal trade in zebra from countries where thedisease is currently active. A similar if not greaterrisk exists for the Middle East which experienced
incursions of AHS more frequently than any otherregion or country.

As the most recent occurrence of AHS in
Thailand has shown, distance is no guarantee ofsafety from the risk of introduction of this disease.
Thailand is approximately 6,000 miles distant from
where the virus responsible for this event probably
originated, and the furthest east in Asia where
AHS has ever been recorded. The most plausible
explanation as to the source of virus lies in the factthat a shipment of zebra arrived in Thailand three
to four weeks before the first AHS outbreak of thedisease was discovered. Zebra are considered thenatural reservoir of the virus, developing viremias
lasting up to 40 days.
This would not be the first occasion that importation of zebra from a country in which AHS
is a seasonal occurrence has been implicated in the
introduction of disease into a disease-free country.
A shipment of zebra was the confirmed source of
this virus for a major disease event that occurred in
Spain in 1987 and subsequently involved Portugal
and Morocco.
International trade in wildlife, both legal andillegal, is believed to have increased significantly
in recent years. What happened in the Iberian
Peninsula in 1987 and Thailand in 2020 highlights
the inherent risks of introducing a disease, such as
AHS, into previously disease-free countries.
The influence of climate change and global
warming on the epidemiology of AHS must also be
considered vis-à-vis the threat it poses for a diseasefree country. Increased ambient temperatures andreduced rainfall over a period of years has resulted
in more widespread geographic distribution ofsome of the major vectors of AHS, especially C.
imicola, in southern Europe. An increase in ambient temperature can influence not only the life
cycle of the Culicoides vector but also replicationof the virus in the vector. As temperatures rise, theinfection rate in Culicoides midges increases andtransmission of the virus can occur sooner, however
there is a concomitant decrease in the survival rateof the adult Culicoides. The overall result of thesechanges is a higher transmission rate of the virus
in a country possibly at risk of the introductionof AHS.

The occurrence in Thailand and the very recent
confirmation of AHS in Malaysia underscore theimportance of increasing awareness and familiarity with this dreaded disease among animal healthofficials, veterinarians and members of the equine
industry around the world. The potential consequences of AHS for the health of a country’s equine
population and economy highlight the need foran adequate level of national preparedness in a)minimizing the risk of introduction of this disease,b) maintaining a program of active surveillance
for the disease and c) having a response plan inplace in the remote event of the introduction of
the disease.
The take-home message from past and recent
occurrences of AHS is that there is no room forcomplacency over the potential threat it represents
for disease free-countries.
CONTACT:
Peter Timoney, MVB, MS, PhD, FRCVS
ptimoney@uky.edu(859) 218-1094
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, Kentucky

N AT I O N A L

Consequences of Wildfires on the Health of Horses

W

Swelling of the supraorbital fossa, eyelids and facial tissues, and bilateral
tearing of a horse affected with the cardiac form of African horse sickness.
COURTESY DR. M. RODRIGUEZ

ildfires have become the new normal formany areas of the world, and subsequent
health consequences have emerged as an important problem affecting large numbers of horses.
For those of us in California with a Mediterranean
climate, large areas are affected by unrelenting
fires, which produce a particular challenge tohorse owners and those providing veterinary care.
There is a paucity of education and training indisaster and emergency response in veterinary
curricula, including the health consequences ofwildfires.
Wildfires can create health problems in horses
by direct and indirect exposure to flames andsmoke, injury during flight or evacuation, and/or
disruption of the horse’s food and water sources.
Wildfire-smoke health effects include primary
smoke exposure with direct smoke inhalation andsecondary smoke-related air quality issues in areas
adjacent to fires where smoke has permeated theenvironment. Wildfire smoke reduces air quality.
It contains small amounts of the toxic gases within
the smoke and particulate matter, soot, and othersubstances depending on what has burned. Particulate matter within smoke is microscopic andquickly descends into the lower airways of horses
producing bronchial and pulmonary inflammation. Eye and nasal irritation, coughing, andincreased respiratory efforts may be observed primarily in horses with a history of heaves or recurrent airway obstruction disorders. Published daily
reports of air quality indexes that guide humans
should be considered for determining horse-related
activities. Events that induce increased respiratory

efforts may need to be postponed, and horses withmassive smoke exposure may need four to six weeks
to recover completely from lower airway inflammation.
Horses with elevated respiratory rates or persistent cough may require veterinary intervention,
including bronchial dilators, airway hydration, andfurther testing. Smoke inhalation from immediate
association with fire can produce thermal injury
to the lungs from hot gases and the toxic effectsof the smoke components. Often these horses also
show evidence of thermal skin injuries.
Thermal injury burns to the skin, eyes, limbs,
and hoofs can be seen in horses exposed to excessive
heat and flames. Horses can incur first-, second-,
and third-degree burns. The extent of affected bodysurface area and the degree of burns can determine
prognosis. Equine burn victims may require daily
treatments lasting several weeks.
Flight-related injuries may be diverse and occur
when horses are fleeing the loud noises associatedwith rapidly approaching wildfires and related
responses of emergency personnel and fire suppression vehicles.
Horses left behind during evacuation may
remain uninjured by the fire. However, they canbe without food and water for extended periods,
because owners are often prevented from returning
to the affected area for several days.
Horses are frequently evacuated from areas at
risk. Evacuation carries many risks to horses associated with trailer loading mishaps and injuries,
exposure to infectious diseases due to housing
in new areas with high densities of horses, and