Equine Disease Quarterly Newsletter

5

3. Communicate with your veterinarian and withthe manager or resident veterinarian at any
facility to which you are taking your horse. Is
there an outbreak situation? If so, re-evaluate
your horse’s vaccination status, and re-evaluate
exposing your horse to flu.
4. Biosecurity from infectious diseases is best enforced by avoiding exposure whenever possible.
For farms, the best biosecurity is obtained byquarantining newly arriving horses away fromthe general herd for sufficient time to assurethat the new arrivals are not bringing diseases
with them. EI is transmitted through the air by
coughing and indirectly on hands or clothing/equipment (fomites) that have been in contact
with an infected horse.
CONTACT:
Thomas Chambers, PhD
tmcham1@uky.edu(859) 218-1126
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, KY

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

APRIL 2019
Volume 28, Number 2

C O M M E N TA RY
KENTUCKY
IN THIS ISSUE

Equine Neorickettsiosis: Incidence in Kentucky in 2018

E

quine neorickettsiosis (EN), more commonly
known as Potomac horse fever, is an equinespecific bacterial disease caused by Neorickettsia
risticii. The disease was first reported in the USA
in 1979 as a sporadic condition observed in horses
pastured in proximity to the Potomac River. Current distribution is now known to extend far beyond the northeastern United States and has beenreported in 43 states in the USA; three provincesin Canada; Uruguay and Brazil in South America;
France and the Netherlands in Europe; and in
India. The disease is often associated with horses
grazing pastures bordering creeks or rivers. Equine
neorickettsiosis is seasonal in occurrence, with the
majority of outbreaks in Kentucky reported in Julythrough September.
The disease is not contagious per se; infection
is naturally acquired by horses accidentally ingesting aquatic insects harboring metacercariae (fluke
larvae) infected with N. risticii.
The life cycle of the bacterium involves operculate freshwater snails and aquatic insects viz
mayflies and caddisflies, the latter being the sourceof infection for horses.
Outbreaks of EN comprise isolated or multiple
cases of the disease on a premises. Experiencehas shown that the disease once confirmed on apremises or in a particular area, tends to recur insubsequent years.

Neorickettsia risticii can cause an acute enterocolitis in susceptible horses that is clinically manifest
by fever, colic of variable severity and profuse
diarrhea. All ages and breeds of horses are at riskof developing the disease. Infections in pregnant
mares can give rise to abortion immediately following infection or months after the resolutionof clinical signs.
Equine neorickettsiosis has been recorded in
Kentucky for a significant number of years. Incidence of the disease can be very variable withincreased case numbers frequently seen in years
with high rainfalls in the spring followed by above
average temperatures in late spring/early summer.
In 2018, the disease was first confirmed in
Kentucky on June 1st. Over the period extending
through the week of 25th August, 26 cases werediagnosed. This figure is probably under-representative of the true incidence of the disease. The
case definition for EN was based on presence ofcharacteristic clinical signs together with a positive
polymerase chain reaction (PCR) test result for thecausal bacterium.
A breakdown of the total number of cases
revealed that the disease was confirmed in ninecounties, the majority in central Kentucky (Figure1). Affected horses ranged from one to 17 yearsof age. The preponderance of cases (20) was seen
in mares. Although the majority of cases were in
Thoroughbreds (18), the disease was recorded in
six other breeds. Of the 26 reported cases in thestate, six died and the remainder survived.

Commentary
International
Fourth Quarter2018  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2Sarcoids .  .  .  .  .  .  .  .  .  .  .  .  . 3National
Equine Influenza  .  .  .  . 4Kentucky

To minimize losses from EN, horsemen wereencouraged to review the environment in which
they kept their horses and to consult with theirveterinarian on strategies that might be used tomitigate disease risk. Recommendation was also
given to minimize the opportunity for horses toingest aquatic insects by turning off lighting in andaround barns and other areas at nighttime.
CONTACT:
E.S. Rusty Ford
Rusty.ford@ky.gov
Office of the Kentucky State VeterinarianFrankfort, KY

EquineNeorickettsiosis  .  .  .  .  . 5

Figure 1. Potomac Horse Fever Cases in
Kentucky in 2018 (confirmed cases).

65
2 3 4 9
7 8

1

Cases

Cases

Cases

1 Metcalfe.................. 1
2 Shelby ..................... 3
3 Franklin................... 3

4 Scott.......................11
5 Harrison .................. 1
6 Bracken ................... 1

7 Woodford............... 3
8 Fayette .................... 3
9 Bourbon ...............11

Office of the Kentucky State Veterinarian
Updated August 25, 2018

Total confirmed cases: 26
College of Agriculture,
Food and Environment
Department of
Veterinary ScienceT

he recent increased incidence of equine
influenza in the United States and abroadnecessitates implementation of prevention andcontrol strategies to protect the health of theequine population. Although vaccination plays
an important role, it should not be relied on as
the sole preventative. Similar to other influenza
viruses, equine influenza virus mutates over timeand vaccines must be periodically updated to keep
current with circulating viruses. Horses that havebeen vaccinated in accordance with manufacturer’slabel instructions and the recommendations ofAmerican Association of Equine Practitioners
may be protected against equine influenza. Studies suggest the use of the modified live intranasal
vaccine in previously unvaccinated horses canprovide protection within five days of primaryadministration. However, no vaccine is 100%
effective. Investigations into recent cases indicatethat vaccinated horses can develop mild clinicalsigns of short duration, whereas unvaccinatedhorses are more severely affected and more likely
to develop secondary pneumonia and pleuritis.
Implementation of biosecurity measures is essential to protecting the health of horses during
influenza season. As influenza virus is spread most
readily through nose-to-nose contact, it is criticalto limit horse-to-horse contact and require strict
isolation of new arrivals and sick horses. Infectedanimals should be kept at a minimum distance of
50 yards from healthy horses.
If no suitable permanent isolation stable is available, then designate an area on the property wherea temporary isolation structure can be erected.
When no appropriate onsite isolation areas are
identified, consider appropriate off-site isolation
facilities such as vacant barns, empty fair or event
grounds, or veterinary clinics. To prevent virustransmission, designate personnel and equipment
to the isolation area. Disposable coveralls, gloves,and boot covers should be used when handlinghorses in isolation. Personnel who must care foranimals both in and outside of isolation should
handle healthy animals first and isolated animals
last. Individuals caring for exposed or infectedhorses should utilize alcohol-based hand sanitizers
after handling all horses.
Influenza virus can be inactivated by exposure
to sunlight or by use of disinfectants. The virus canremain viable for up to 2 days on contaminatedsurfaces, specifically solid surfaces of stall door
latches. Thus, any shared equipment should bethoroughly cleaned and disinfected between uses.
The critical factor in controlling and preventing the spread of influenza virus is monitoring thehealth of all equids. Monitoring includes taking
body temperatures twice daily and recording allclinical observations. Only healthy horses, whichhave been monitored, should be permitted to leave
the premises. Any horse showing clinical signs ofrespiratory disease should be immediately isolated
and examined by a veterinarian. Horses should
remain isolated until they’re clinically healthy andno longer shedding virus. As respiratory sheddingof the influenza virus can persist for 7-10 days postinfection in a naïve animal, horses should remain
isolated for a minimum of 14 days.
Appropriate use of vaccination and implementing biosecurity measures are critical to protecting
the equine industry from highly contagious equine
influenza virus.
CONTACT:
Katie Flynn, BVMS
katherine.flynn@cdfa.ca.gov(916) 900-5039
California Department of Food and Agriculture, Animal
Health Branch
Sacramento, CA

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

N AT I O N A L

Fourth Quarter 2018

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Cynthia Gaskill

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita Fleming
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 equine disease outbreaks.
The Republic of South Africa (RSA) reported
isolated cases of African horse sickness in known
infected areas that included the provinces of theEastern Cape, Gauteng, and KwaZulu-Natal.
Occurrence of the disease is as expected for thistime of year.
Equine influenza was recorded in Ecuador (oneoutbreak), France (three outbreaks), and the UK
which considers the disease to be endemic. The disease is also endemic in the USA, being confirmed
in seven states, with some outbreaks characterizedby multiple cases of the disease.
Canada, France, Germany, Ireland, Switzerland,
the UK, and the USA reported multiple outbreaksof strangles. The number of confirmed outbreaks/
cases included two in Canada, 28 in France, fourin Germany, five in Ireland and four in Switzerland. The disease was reported to be endemic
in the UK and in the USA, where 34 outbreaks
were confirmed in 18 states involving at least 68
affected horses.
Equine herpesvirus 1 related diseases wererecorded by France, Germany, Ireland, Japan,
the RSA, the UK, and the USA. Febrile illness
was reported by the RSA and the USA. Respiratory disease was confirmed in France (eight outbreaks), Germany (one outbreak), the RSA (oneoutbreak), and the UK (one outbreak). Abortiondue to EHV-1 was recorded in France (two cases),Germany (single cases on two premises), Ireland(single cases on four premises), Japan (two cases on
separate premises), and the USA (five cases). The
RSA, UK, and USA reported outbreaks of EHV-1
myeloencephalopathy. The RSA and the UK eachreported a single case of the disease, whereas the
USA confirmed four cases involving premises in
Arizona and California.
Equine herpesvirus 4 (EHV-4) respiratory
disease was diagnosed in France (26 outbreaks),
Germany (one outbreak involving four cases ofthe disease), the UK (seven outbreaks), and theUSA (one case). One case of EHV-4 abortion was
confirmed in the USA.

Multiple cases of equine herpesvirus 2 and/or 5
infection were reported by the USA, some associated with evidence of respiratory disease.
France recorded one case of subclinical equine
arteritis virus infection and two cases of abortion
caused by the virus. Germany confirmed the carrierstate in one stallion.
Equine infectious anemia was diagnosed in
Canada (three cases), France (one case), and theUSA (three cases in Colorado and two in Texas).
The RSA and Switzerland reported cases of
equine piroplasmosis. The disease is endemic in the
RSA with cases confirmed in six provinces. One
case of Theileria equi was diagnosed in Switzerland.
Contagious equine metritis was recorded byGermany (two stallions on separate premises)
and South Korea (13 positive venereal swabs from2,236 stallions and broodmares tested as part of anational survey).
The USA confirmed four cases of leptospiralabortion and two cases of equine neorickettsiosis
abortion in Kentucky.
Germany reported one case of salmonellosis(serogroup not specified).
An outbreak of rotaviral enteritis was recorded
by Argentina; a total of ten 2- to 4-month-old
foals were affected on one premises, all of which
had been vaccinated.
The USA reported eight cases of infection with
Lawsonia intracellularis in Kentucky.
The fourth quarter of 2018 saw a sharp decline
in the number of cases of Eastern equine encephalomyelitis confirmed in the USA, with only threecases recorded, all in New York State.
West Nile virus activity was reported in Canada(3 cases), France (3 case), Portugal (1 case), Tunisia(7 cases), Turkey (1 case), and the USA (70 cases).
Rhodococcal-related disease is endemic in theUSA. Even though only three outbreaks were recorded in the fourth quarter, this is not reflectiveof the true incidence of the disease.
Singapore confirmed one case of Old world
screwworm infection in a horse, and Switzerland
reported more than four cases of Atypical Myopathy during October 2018.

Sarcoids

S

arcoids are believed to be the most common
skin tumor of the horse and affect about
2% of horses worldwide. Although they do notmetastasize (spread to distant locations), they
undoubtedly cause welfare concerns, especiallyin the ulcerated “fibroblastic” form. This may bethrough discomfort from the lesions themselves,from fly interference with the lesions, and also
from administered treatments. In their most extreme forms, they can affect eyelid function andlead to secondary ulceration of the eye’s surface(Figure 1). Clearly, they are not a “benign” lesion, despite their benign classification, and theyshould never be ignored. The presence of sarcoids
also has financial implications not only due to the(sometimes very high) cost of treatment, but also
due to reduced resale value.
There is compelling evidence that sarcoids arecaused by a bovine papillomavirus which is believed to be transmitted by flies, most likely from
infected cattle, but possibly also from infectedhorses. It remains unclear exactly how the virus
leads to neoplastic (cancerous) change, or why
the virus is able to cause disease in more than one
species. Interestingly, a (human) papillomavirus
also is responsible for the vast majority of cases ofcervical cancer and an increasingly large proportionof tumors of the head and neck in humans; clearly
there is much to be learned about the implicationsof infection with papillomaviruses in all species.
There is little doubt that there is a heritablecomponent to the disease. In warmbloods, theheritability has been well demonstrated: Breeding
two sarcoid-affected horses vastly increases therisk of producing a horse that develops sarcoids atsome stage in its life. There also appear to be breedrelated differences in sarcoid risk: Thoroughbreds
are more likely to develop sarcoids than Standardbreds, and Lipizzaners seem more resistant tosarcoid development. Unlike melanomas, there isno color predisposition and gender doesn’t affectthe chance of developing the disease. Specific genevariations, noted in horses with sarcoids, are also
associated with virally induced cancers in humans.
The reasons for this association are unclear, but it islikely due to differences in immune function andmay explain the apparent breed-specific variationin sarcoid risk.
Treatment options for sarcoids are numerous,
with no one option being suitable for every case.
Traditionally, sarcoids were often left without treatment, but as they almost invariably become larger
and more difficult to treat, early intervention isstrongly recommended to avoid long-term sequelae. Treatment may involve topical or intra-lesional
chemotherapy or immune modulators, surgicalprocedures, or radiotherapy. Electrochemotherapy
is a relatively new alternative treatment option withapparently very good results, but it unfortunately
necessitates the use of multiple general anaesthetics, so the risks must be carefully considered.
Appropriate treatment selection is largely dictated by the location and type of the lesion (Figure2). Laser surgical excision is the author’s treatmentof choice for the majority of lesions in locations
other than around the eye; periocular lesions
are treated via radiotherapy with great success.
Reported success rates for laser surgical excision
are in the order of 83% and for radiotherapy arearound 90%; compared to other treatment options
they represent the least risk to the horse and leadto the best results. However, not every lesion—or
horse—is a suitable candidate for these treatments,
and the key is to select the method most likely
to be successful in the first instance. Recurrent
sarcoids become increasingly difficult to manage
and convey a far worse prognosis than those appropriately treated in the first place.
CONTACT:
Anna Hollis, BVetMed DACVIM DipECEIM MRCVS
anna.hollis@aht.org.uk
Animal Health Trust
Newmarket, UK

Equine Influenza

E

Figure 1.
Horse with sarcoid lesion
before treatment.

Figure 2.
Horse 2½ years after
treatment.

quine influenza (EI) is considered endemic
in both the USA and Europe, but the viruses
causing EI differ slightly. For many years, the viruses in circulation in the USA have been ‘Florida
clade 1’ (FC1) whereas in Europe they have been
‘Florida clade 2’ (FC2). These clades split apart in
2003; circulation of FC2 ceased in the USA around2005, and by 2010 there was no evidence of FC1
in circulation in Europe. Because of the extensive
movement of horses between North America andEurope, the international panel of EI experts hasrecommended for the last ten years that EI vaccines contain representatives of both FC1 andFC2. Some (not all) available EI vaccines meetthis recommendation.
EI virus activity has recently increased in theUSA, Europe, and Nigeria. Normally, the virus
circulates at a variable, but fairly low, level in theUSA, but virus activity surged in the last threemonths of 2018 with outbreaks in 12 states. An
extensive EI event occurred in a donkey sanctuary
in Nigeria. For the first time since 2015, multiple
outbreaks of EI were reported during January andFebruary of 2019 in France, Belgium, the Netherlands, Germany, Ireland, England, and Scotland.
In England, it resulted in a temporary lockdownof at least 174 premises and cancellation of racing for 6 days in February. Outbreaks were also
reported in California, Arizona, Ohio, Indiana,
and Washington State.
Some of the horses in these outbreaks, in boththe USA and Europe, had been vaccinated for EI,
raising the question: Is this a new strain that is notin the vaccines? The answer appears to be no. While
the virus causing the Nigerian EI event is stilluncharacterized, genetic analysis of isolates fromboth England and the USA confirms these as FC1.
There are two mutations that make them different
from the recommended vaccines strains, but arethese important? That is still under investigation.
The absence of FC1 from European circulationmeans their horses have no natural immunity andare dependent on vaccination for protection. The
reports from England indicate that the clinicaldisease is of shorter duration and less severe invaccinated horses; this would indicate the vaccines
are working, at least partially. Milder disease invaccinated horses may reflect an inadequate level ofprotective immunity following exposure to unvaccinated horses shedding large quantities of virus.
What should owners and veterinarians do toprotect their horses from EI?
1. Familiarize yourself with the clinical signs of EI.
Often the very first sign is a harsh cough. Othersigns include fever and nasal discharge, which
is usually watery (serous) at first and then turns
thick and yellow (mucopurulent). The horse
may show unusually rapid breathing (tachypnea) or lose its appetite (anorexia). Sometimes
there may be enlarged submandibular lymph
nodes or dependent limb edema. Keep inmind that not all these signs may be present.
Horses can be infected and still appear normal(subclinical infection), especially if they havebeen previously vaccinated. Other infectious
agents can produce clinical signs that look like
EI, but aren’t. EHV-1/4 or strangles (Streptococcus equi) are examples. Have your veterinariancollect a nasal swab, or ideally a nasopharyngeal
swab (which goes beyond the nostrils into theback of the throat), and send it to a veterinary
diagnostic laboratory to confirm a diagnosis.
Information on nasal-swabbing can be found at
http://vetsci.ca.uky.edu/services. If your horse
does develop clinical signs of EI, then the ruleof thumb is that for every day of fever, it should
be stall-rested for a week.
2. Vaccinate your horses using a vaccine that
protects against both FC1 and FC2 viruses.
Horses’ antibody responses to vaccination do
not last indefinitely, so if your horse has notbeen vaccinated for six months or more, then it
is due for a booster. If it has been three months
or less since the last booster, then hopefully
your horse’s immunity should be at its peak.
Consult your veterinarian and refer to the
AAEP Guidelines (https://aaep.org/guidelines/
vaccination-guidelines/risk-based-vaccinationguidelines/equine-influenza). In the event of an
EI outbreak, where your horse may potentiallybe exposed, vaccination in the immediate faceof the event might help if there is sufficienttime—at least a week—for the horse’s immune
system to start making antibodies.

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

N AT I O N A L

Fourth Quarter 2018

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Cynthia Gaskill

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita Fleming
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 equine disease outbreaks.
The Republic of South Africa (RSA) reported
isolated cases of African horse sickness in known
infected areas that included the provinces of theEastern Cape, Gauteng, and KwaZulu-Natal.
Occurrence of the disease is as expected for thistime of year.
Equine influenza was recorded in Ecuador (oneoutbreak), France (three outbreaks), and the UK
which considers the disease to be endemic. The disease is also endemic in the USA, being confirmed
in seven states, with some outbreaks characterizedby multiple cases of the disease.
Canada, France, Germany, Ireland, Switzerland,
the UK, and the USA reported multiple outbreaksof strangles. The number of confirmed outbreaks/
cases included two in Canada, 28 in France, fourin Germany, five in Ireland and four in Switzerland. The disease was reported to be endemic
in the UK and in the USA, where 34 outbreaks
were confirmed in 18 states involving at least 68
affected horses.
Equine herpesvirus 1 related diseases wererecorded by France, Germany, Ireland, Japan,
the RSA, the UK, and the USA. Febrile illness
was reported by the RSA and the USA. Respiratory disease was confirmed in France (eight outbreaks), Germany (one outbreak), the RSA (oneoutbreak), and the UK (one outbreak). Abortiondue to EHV-1 was recorded in France (two cases),Germany (single cases on two premises), Ireland(single cases on four premises), Japan (two cases on
separate premises), and the USA (five cases). The
RSA, UK, and USA reported outbreaks of EHV-1
myeloencephalopathy. The RSA and the UK eachreported a single case of the disease, whereas the
USA confirmed four cases involving premises in
Arizona and California.
Equine herpesvirus 4 (EHV-4) respiratory
disease was diagnosed in France (26 outbreaks),
Germany (one outbreak involving four cases ofthe disease), the UK (seven outbreaks), and theUSA (one case). One case of EHV-4 abortion was
confirmed in the USA.

Multiple cases of equine herpesvirus 2 and/or 5
infection were reported by the USA, some associated with evidence of respiratory disease.
France recorded one case of subclinical equine
arteritis virus infection and two cases of abortion
caused by the virus. Germany confirmed the carrierstate in one stallion.
Equine infectious anemia was diagnosed in
Canada (three cases), France (one case), and theUSA (three cases in Colorado and two in Texas).
The RSA and Switzerland reported cases of
equine piroplasmosis. The disease is endemic in the
RSA with cases confirmed in six provinces. One
case of Theileria equi was diagnosed in Switzerland.
Contagious equine metritis was recorded byGermany (two stallions on separate premises)
and South Korea (13 positive venereal swabs from2,236 stallions and broodmares tested as part of anational survey).
The USA confirmed four cases of leptospiralabortion and two cases of equine neorickettsiosis
abortion in Kentucky.
Germany reported one case of salmonellosis(serogroup not specified).
An outbreak of rotaviral enteritis was recorded
by Argentina; a total of ten 2- to 4-month-old
foals were affected on one premises, all of which
had been vaccinated.
The USA reported eight cases of infection with
Lawsonia intracellularis in Kentucky.
The fourth quarter of 2018 saw a sharp decline
in the number of cases of Eastern equine encephalomyelitis confirmed in the USA, with only threecases recorded, all in New York State.
West Nile virus activity was reported in Canada(3 cases), France (3 case), Portugal (1 case), Tunisia(7 cases), Turkey (1 case), and the USA (70 cases).
Rhodococcal-related disease is endemic in theUSA. Even though only three outbreaks were recorded in the fourth quarter, this is not reflectiveof the true incidence of the disease.
Singapore confirmed one case of Old world
screwworm infection in a horse, and Switzerland
reported more than four cases of Atypical Myopathy during October 2018.

Sarcoids

S

arcoids are believed to be the most common
skin tumor of the horse and affect about
2% of horses worldwide. Although they do notmetastasize (spread to distant locations), they
undoubtedly cause welfare concerns, especiallyin the ulcerated “fibroblastic” form. This may bethrough discomfort from the lesions themselves,from fly interference with the lesions, and also
from administered treatments. In their most extreme forms, they can affect eyelid function andlead to secondary ulceration of the eye’s surface(Figure 1). Clearly, they are not a “benign” lesion, despite their benign classification, and theyshould never be ignored. The presence of sarcoids
also has financial implications not only due to the(sometimes very high) cost of treatment, but also
due to reduced resale value.
There is compelling evidence that sarcoids arecaused by a bovine papillomavirus which is believed to be transmitted by flies, most likely from
infected cattle, but possibly also from infectedhorses. It remains unclear exactly how the virus
leads to neoplastic (cancerous) change, or why
the virus is able to cause disease in more than one
species. Interestingly, a (human) papillomavirus
also is responsible for the vast majority of cases ofcervical cancer and an increasingly large proportionof tumors of the head and neck in humans; clearly
there is much to be learned about the implicationsof infection with papillomaviruses in all species.
There is little doubt that there is a heritablecomponent to the disease. In warmbloods, theheritability has been well demonstrated: Breeding
two sarcoid-affected horses vastly increases therisk of producing a horse that develops sarcoids atsome stage in its life. There also appear to be breedrelated differences in sarcoid risk: Thoroughbreds
are more likely to develop sarcoids than Standardbreds, and Lipizzaners seem more resistant tosarcoid development. Unlike melanomas, there isno color predisposition and gender doesn’t affectthe chance of developing the disease. Specific genevariations, noted in horses with sarcoids, are also
associated with virally induced cancers in humans.
The reasons for this association are unclear, but it islikely due to differences in immune function andmay explain the apparent breed-specific variationin sarcoid risk.
Treatment options for sarcoids are numerous,
with no one option being suitable for every case.
Traditionally, sarcoids were often left without treatment, but as they almost invariably become larger
and more difficult to treat, early intervention isstrongly recommended to avoid long-term sequelae. Treatment may involve topical or intra-lesional
chemotherapy or immune modulators, surgicalprocedures, or radiotherapy. Electrochemotherapy
is a relatively new alternative treatment option withapparently very good results, but it unfortunately
necessitates the use of multiple general anaesthetics, so the risks must be carefully considered.
Appropriate treatment selection is largely dictated by the location and type of the lesion (Figure2). Laser surgical excision is the author’s treatmentof choice for the majority of lesions in locations
other than around the eye; periocular lesions
are treated via radiotherapy with great success.
Reported success rates for laser surgical excision
are in the order of 83% and for radiotherapy arearound 90%; compared to other treatment options
they represent the least risk to the horse and leadto the best results. However, not every lesion—or
horse—is a suitable candidate for these treatments,
and the key is to select the method most likely
to be successful in the first instance. Recurrent
sarcoids become increasingly difficult to manage
and convey a far worse prognosis than those appropriately treated in the first place.
CONTACT:
Anna Hollis, BVetMed DACVIM DipECEIM MRCVS
anna.hollis@aht.org.uk
Animal Health Trust
Newmarket, UK

Equine Influenza

E

Figure 1.
Horse with sarcoid lesion
before treatment.

Figure 2.
Horse 2½ years after
treatment.

quine influenza (EI) is considered endemic
in both the USA and Europe, but the viruses
causing EI differ slightly. For many years, the viruses in circulation in the USA have been ‘Florida
clade 1’ (FC1) whereas in Europe they have been
‘Florida clade 2’ (FC2). These clades split apart in
2003; circulation of FC2 ceased in the USA around2005, and by 2010 there was no evidence of FC1
in circulation in Europe. Because of the extensive
movement of horses between North America andEurope, the international panel of EI experts hasrecommended for the last ten years that EI vaccines contain representatives of both FC1 andFC2. Some (not all) available EI vaccines meetthis recommendation.
EI virus activity has recently increased in theUSA, Europe, and Nigeria. Normally, the virus
circulates at a variable, but fairly low, level in theUSA, but virus activity surged in the last threemonths of 2018 with outbreaks in 12 states. An
extensive EI event occurred in a donkey sanctuary
in Nigeria. For the first time since 2015, multiple
outbreaks of EI were reported during January andFebruary of 2019 in France, Belgium, the Netherlands, Germany, Ireland, England, and Scotland.
In England, it resulted in a temporary lockdownof at least 174 premises and cancellation of racing for 6 days in February. Outbreaks were also
reported in California, Arizona, Ohio, Indiana,
and Washington State.
Some of the horses in these outbreaks, in boththe USA and Europe, had been vaccinated for EI,
raising the question: Is this a new strain that is notin the vaccines? The answer appears to be no. While
the virus causing the Nigerian EI event is stilluncharacterized, genetic analysis of isolates fromboth England and the USA confirms these as FC1.
There are two mutations that make them different
from the recommended vaccines strains, but arethese important? That is still under investigation.
The absence of FC1 from European circulationmeans their horses have no natural immunity andare dependent on vaccination for protection. The
reports from England indicate that the clinicaldisease is of shorter duration and less severe invaccinated horses; this would indicate the vaccines
are working, at least partially. Milder disease invaccinated horses may reflect an inadequate level ofprotective immunity following exposure to unvaccinated horses shedding large quantities of virus.
What should owners and veterinarians do toprotect their horses from EI?
1. Familiarize yourself with the clinical signs of EI.
Often the very first sign is a harsh cough. Othersigns include fever and nasal discharge, which
is usually watery (serous) at first and then turns
thick and yellow (mucopurulent). The horse
may show unusually rapid breathing (tachypnea) or lose its appetite (anorexia). Sometimes
there may be enlarged submandibular lymph
nodes or dependent limb edema. Keep inmind that not all these signs may be present.
Horses can be infected and still appear normal(subclinical infection), especially if they havebeen previously vaccinated. Other infectious
agents can produce clinical signs that look like
EI, but aren’t. EHV-1/4 or strangles (Streptococcus equi) are examples. Have your veterinariancollect a nasal swab, or ideally a nasopharyngeal
swab (which goes beyond the nostrils into theback of the throat), and send it to a veterinary
diagnostic laboratory to confirm a diagnosis.
Information on nasal-swabbing can be found at
http://vetsci.ca.uky.edu/services. If your horse
does develop clinical signs of EI, then the ruleof thumb is that for every day of fever, it should
be stall-rested for a week.
2. Vaccinate your horses using a vaccine that
protects against both FC1 and FC2 viruses.
Horses’ antibody responses to vaccination do
not last indefinitely, so if your horse has notbeen vaccinated for six months or more, then it
is due for a booster. If it has been three months
or less since the last booster, then hopefully
your horse’s immunity should be at its peak.
Consult your veterinarian and refer to the
AAEP Guidelines (https://aaep.org/guidelines/
vaccination-guidelines/risk-based-vaccinationguidelines/equine-influenza). In the event of an
EI outbreak, where your horse may potentiallybe exposed, vaccination in the immediate faceof the event might help if there is sufficienttime—at least a week—for the horse’s immune
system to start making antibodies.

2

3

4

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

N AT I O N A L

Fourth Quarter 2018

T

Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Cynthia Gaskill

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita Fleming
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 equine disease outbreaks.
The Republic of South Africa (RSA) reported
isolated cases of African horse sickness in known
infected areas that included the provinces of theEastern Cape, Gauteng, and KwaZulu-Natal.
Occurrence of the disease is as expected for thistime of year.
Equine influenza was recorded in Ecuador (oneoutbreak), France (three outbreaks), and the UK
which considers the disease to be endemic. The disease is also endemic in the USA, being confirmed
in seven states, with some outbreaks characterizedby multiple cases of the disease.
Canada, France, Germany, Ireland, Switzerland,
the UK, and the USA reported multiple outbreaksof strangles. The number of confirmed outbreaks/
cases included two in Canada, 28 in France, fourin Germany, five in Ireland and four in Switzerland. The disease was reported to be endemic
in the UK and in the USA, where 34 outbreaks
were confirmed in 18 states involving at least 68
affected horses.
Equine herpesvirus 1 related diseases wererecorded by France, Germany, Ireland, Japan,
the RSA, the UK, and the USA. Febrile illness
was reported by the RSA and the USA. Respiratory disease was confirmed in France (eight outbreaks), Germany (one outbreak), the RSA (oneoutbreak), and the UK (one outbreak). Abortiondue to EHV-1 was recorded in France (two cases),Germany (single cases on two premises), Ireland(single cases on four premises), Japan (two cases on
separate premises), and the USA (five cases). The
RSA, UK, and USA reported outbreaks of EHV-1
myeloencephalopathy. The RSA and the UK eachreported a single case of the disease, whereas the
USA confirmed four cases involving premises in
Arizona and California.
Equine herpesvirus 4 (EHV-4) respiratory
disease was diagnosed in France (26 outbreaks),
Germany (one outbreak involving four cases ofthe disease), the UK (seven outbreaks), and theUSA (one case). One case of EHV-4 abortion was
confirmed in the USA.

Multiple cases of equine herpesvirus 2 and/or 5
infection were reported by the USA, some associated with evidence of respiratory disease.
France recorded one case of subclinical equine
arteritis virus infection and two cases of abortion
caused by the virus. Germany confirmed the carrierstate in one stallion.
Equine infectious anemia was diagnosed in
Canada (three cases), France (one case), and theUSA (three cases in Colorado and two in Texas).
The RSA and Switzerland reported cases of
equine piroplasmosis. The disease is endemic in the
RSA with cases confirmed in six provinces. One
case of Theileria equi was diagnosed in Switzerland.
Contagious equine metritis was recorded byGermany (two stallions on separate premises)
and South Korea (13 positive venereal swabs from2,236 stallions and broodmares tested as part of anational survey).
The USA confirmed four cases of leptospiralabortion and two cases of equine neorickettsiosis
abortion in Kentucky.
Germany reported one case of salmonellosis(serogroup not specified).
An outbreak of rotaviral enteritis was recorded
by Argentina; a total of ten 2- to 4-month-old
foals were affected on one premises, all of which
had been vaccinated.
The USA reported eight cases of infection with
Lawsonia intracellularis in Kentucky.
The fourth quarter of 2018 saw a sharp decline
in the number of cases of Eastern equine encephalomyelitis confirmed in the USA, with only threecases recorded, all in New York State.
West Nile virus activity was reported in Canada(3 cases), France (3 case), Portugal (1 case), Tunisia(7 cases), Turkey (1 case), and the USA (70 cases).
Rhodococcal-related disease is endemic in theUSA. Even though only three outbreaks were recorded in the fourth quarter, this is not reflectiveof the true incidence of the disease.
Singapore confirmed one case of Old world
screwworm infection in a horse, and Switzerland
reported more than four cases of Atypical Myopathy during October 2018.

Sarcoids

S

arcoids are believed to be the most common
skin tumor of the horse and affect about
2% of horses worldwide. Although they do notmetastasize (spread to distant locations), they
undoubtedly cause welfare concerns, especiallyin the ulcerated “fibroblastic” form. This may bethrough discomfort from the lesions themselves,from fly interference with the lesions, and also
from administered treatments. In their most extreme forms, they can affect eyelid function andlead to secondary ulceration of the eye’s surface(Figure 1). Clearly, they are not a “benign” lesion, despite their benign classification, and theyshould never be ignored. The presence of sarcoids
also has financial implications not only due to the(sometimes very high) cost of treatment, but also
due to reduced resale value.
There is compelling evidence that sarcoids arecaused by a bovine papillomavirus which is believed to be transmitted by flies, most likely from
infected cattle, but possibly also from infectedhorses. It remains unclear exactly how the virus
leads to neoplastic (cancerous) change, or why
the virus is able to cause disease in more than one
species. Interestingly, a (human) papillomavirus
also is responsible for the vast majority of cases ofcervical cancer and an increasingly large proportionof tumors of the head and neck in humans; clearly
there is much to be learned about the implicationsof infection with papillomaviruses in all species.
There is little doubt that there is a heritablecomponent to the disease. In warmbloods, theheritability has been well demonstrated: Breeding
two sarcoid-affected horses vastly increases therisk of producing a horse that develops sarcoids atsome stage in its life. There also appear to be breedrelated differences in sarcoid risk: Thoroughbreds
are more likely to develop sarcoids than Standardbreds, and Lipizzaners seem more resistant tosarcoid development. Unlike melanomas, there isno color predisposition and gender doesn’t affectthe chance of developing the disease. Specific genevariations, noted in horses with sarcoids, are also
associated with virally induced cancers in humans.
The reasons for this association are unclear, but it islikely due to differences in immune function andmay explain the apparent breed-specific variationin sarcoid risk.
Treatment options for sarcoids are numerous,
with no one option being suitable for every case.
Traditionally, sarcoids were often left without treatment, but as they almost invariably become larger
and more difficult to treat, early intervention isstrongly recommended to avoid long-term sequelae. Treatment may involve topical or intra-lesional
chemotherapy or immune modulators, surgicalprocedures, or radiotherapy. Electrochemotherapy
is a relatively new alternative treatment option withapparently very good results, but it unfortunately
necessitates the use of multiple general anaesthetics, so the risks must be carefully considered.
Appropriate treatment selection is largely dictated by the location and type of the lesion (Figure2). Laser surgical excision is the author’s treatmentof choice for the majority of lesions in locations
other than around the eye; periocular lesions
are treated via radiotherapy with great success.
Reported success rates for laser surgical excision
are in the order of 83% and for radiotherapy arearound 90%; compared to other treatment options
they represent the least risk to the horse and leadto the best results. However, not every lesion—or
horse—is a suitable candidate for these treatments,
and the key is to select the method most likely
to be successful in the first instance. Recurrent
sarcoids become increasingly difficult to manage
and convey a far worse prognosis than those appropriately treated in the first place.
CONTACT:
Anna Hollis, BVetMed DACVIM DipECEIM MRCVS
anna.hollis@aht.org.uk
Animal Health Trust
Newmarket, UK

Equine Influenza

E

Figure 1.
Horse with sarcoid lesion
before treatment.

Figure 2.
Horse 2½ years after
treatment.

quine influenza (EI) is considered endemic
in both the USA and Europe, but the viruses
causing EI differ slightly. For many years, the viruses in circulation in the USA have been ‘Florida
clade 1’ (FC1) whereas in Europe they have been
‘Florida clade 2’ (FC2). These clades split apart in
2003; circulation of FC2 ceased in the USA around2005, and by 2010 there was no evidence of FC1
in circulation in Europe. Because of the extensive
movement of horses between North America andEurope, the international panel of EI experts hasrecommended for the last ten years that EI vaccines contain representatives of both FC1 andFC2. Some (not all) available EI vaccines meetthis recommendation.
EI virus activity has recently increased in theUSA, Europe, and Nigeria. Normally, the virus
circulates at a variable, but fairly low, level in theUSA, but virus activity surged in the last threemonths of 2018 with outbreaks in 12 states. An
extensive EI event occurred in a donkey sanctuary
in Nigeria. For the first time since 2015, multiple
outbreaks of EI were reported during January andFebruary of 2019 in France, Belgium, the Netherlands, Germany, Ireland, England, and Scotland.
In England, it resulted in a temporary lockdownof at least 174 premises and cancellation of racing for 6 days in February. Outbreaks were also
reported in California, Arizona, Ohio, Indiana,
and Washington State.
Some of the horses in these outbreaks, in boththe USA and Europe, had been vaccinated for EI,
raising the question: Is this a new strain that is notin the vaccines? The answer appears to be no. While
the virus causing the Nigerian EI event is stilluncharacterized, genetic analysis of isolates fromboth England and the USA confirms these as FC1.
There are two mutations that make them different
from the recommended vaccines strains, but arethese important? That is still under investigation.
The absence of FC1 from European circulationmeans their horses have no natural immunity andare dependent on vaccination for protection. The
reports from England indicate that the clinicaldisease is of shorter duration and less severe invaccinated horses; this would indicate the vaccines
are working, at least partially. Milder disease invaccinated horses may reflect an inadequate level ofprotective immunity following exposure to unvaccinated horses shedding large quantities of virus.
What should owners and veterinarians do toprotect their horses from EI?
1. Familiarize yourself with the clinical signs of EI.
Often the very first sign is a harsh cough. Othersigns include fever and nasal discharge, which
is usually watery (serous) at first and then turns
thick and yellow (mucopurulent). The horse
may show unusually rapid breathing (tachypnea) or lose its appetite (anorexia). Sometimes
there may be enlarged submandibular lymph
nodes or dependent limb edema. Keep inmind that not all these signs may be present.
Horses can be infected and still appear normal(subclinical infection), especially if they havebeen previously vaccinated. Other infectious
agents can produce clinical signs that look like
EI, but aren’t. EHV-1/4 or strangles (Streptococcus equi) are examples. Have your veterinariancollect a nasal swab, or ideally a nasopharyngeal
swab (which goes beyond the nostrils into theback of the throat), and send it to a veterinary
diagnostic laboratory to confirm a diagnosis.
Information on nasal-swabbing can be found at
http://vetsci.ca.uky.edu/services. If your horse
does develop clinical signs of EI, then the ruleof thumb is that for every day of fever, it should
be stall-rested for a week.
2. Vaccinate your horses using a vaccine that
protects against both FC1 and FC2 viruses.
Horses’ antibody responses to vaccination do
not last indefinitely, so if your horse has notbeen vaccinated for six months or more, then it
is due for a booster. If it has been three months
or less since the last booster, then hopefully
your horse’s immunity should be at its peak.
Consult your veterinarian and refer to the
AAEP Guidelines (https://aaep.org/guidelines/
vaccination-guidelines/risk-based-vaccinationguidelines/equine-influenza). In the event of an
EI outbreak, where your horse may potentiallybe exposed, vaccination in the immediate faceof the event might help if there is sufficienttime—at least a week—for the horse’s immune
system to start making antibodies.

Equine Disease Quarterly Newsletter

5

3. Communicate with your veterinarian and withthe manager or resident veterinarian at any
facility to which you are taking your horse. Is
there an outbreak situation? If so, re-evaluate
your horse’s vaccination status, and re-evaluate
exposing your horse to flu.
4. Biosecurity from infectious diseases is best enforced by avoiding exposure whenever possible.
For farms, the best biosecurity is obtained byquarantining newly arriving horses away fromthe general herd for sufficient time to assurethat the new arrivals are not bringing diseases
with them. EI is transmitted through the air by
coughing and indirectly on hands or clothing/equipment (fomites) that have been in contact
with an infected horse.
CONTACT:
Thomas Chambers, PhD
tmcham1@uky.edu(859) 218-1126
Maxwell H. Gluck Equine Research Center
University of Kentucky
Lexington, KY

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

APRIL 2019
Volume 28, Number 2

C O M M E N TA RY
KENTUCKY
IN THIS ISSUE

Equine Neorickettsiosis: Incidence in Kentucky in 2018

E

quine neorickettsiosis (EN), more commonly
known as Potomac horse fever, is an equinespecific bacterial disease caused by Neorickettsia
risticii. The disease was first reported in the USA
in 1979 as a sporadic condition observed in horses
pastured in proximity to the Potomac River. Current distribution is now known to extend far beyond the northeastern United States and has beenreported in 43 states in the USA; three provincesin Canada; Uruguay and Brazil in South America;
France and the Netherlands in Europe; and in
India. The disease is often associated with horses
grazing pastures bordering creeks or rivers. Equine
neorickettsiosis is seasonal in occurrence, with the
majority of outbreaks in Kentucky reported in Julythrough September.
The disease is not contagious per se; infection
is naturally acquired by horses accidentally ingesting aquatic insects harboring metacercariae (fluke
larvae) infected with N. risticii.
The life cycle of the bacterium involves operculate freshwater snails and aquatic insects viz
mayflies and caddisflies, the latter being the sourceof infection for horses.
Outbreaks of EN comprise isolated or multiple
cases of the disease on a premises. Experiencehas shown that the disease once confirmed on apremises or in a particular area, tends to recur insubsequent years.

Neorickettsia risticii can cause an acute enterocolitis in susceptible horses that is clinically manifest
by fever, colic of variable severity and profuse
diarrhea. All ages and breeds of horses are at riskof developing the disease. Infections in pregnant
mares can give rise to abortion immediately following infection or months after the resolutionof clinical signs.
Equine neorickettsiosis has been recorded in
Kentucky for a significant number of years. Incidence of the disease can be very variable withincreased case numbers frequently seen in years
with high rainfalls in the spring followed by above
average temperatures in late spring/early summer.
In 2018, the disease was first confirmed in
Kentucky on June 1st. Over the period extending
through the week of 25th August, 26 cases werediagnosed. This figure is probably under-representative of the true incidence of the disease. The
case definition for EN was based on presence ofcharacteristic clinical signs together with a positive
polymerase chain reaction (PCR) test result for thecausal bacterium.
A breakdown of the total number of cases
revealed that the disease was confirmed in ninecounties, the majority in central Kentucky (Figure1). Affected horses ranged from one to 17 yearsof age. The preponderance of cases (20) was seen
in mares. Although the majority of cases were in
Thoroughbreds (18), the disease was recorded in
six other breeds. Of the 26 reported cases in thestate, six died and the remainder survived.

Commentary
International
Fourth Quarter2018  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2Sarcoids .  .  .  .  .  .  .  .  .  .  .  .  . 3National
Equine Influenza  .  .  .  . 4Kentucky

To minimize losses from EN, horsemen wereencouraged to review the environment in which
they kept their horses and to consult with theirveterinarian on strategies that might be used tomitigate disease risk. Recommendation was also
given to minimize the opportunity for horses toingest aquatic insects by turning off lighting in andaround barns and other areas at nighttime.
CONTACT:
E.S. Rusty Ford
Rusty.ford@ky.gov
Office of the Kentucky State VeterinarianFrankfort, KY

EquineNeorickettsiosis  .  .  .  .  . 5

Figure 1. Potomac Horse Fever Cases in
Kentucky in 2018 (confirmed cases).

65
2 3 4 9
7 8

1

Cases

Cases

Cases

1 Metcalfe.................. 1
2 Shelby ..................... 3
3 Franklin................... 3

4 Scott.......................11
5 Harrison .................. 1
6 Bracken ................... 1

7 Woodford............... 3
8 Fayette .................... 3
9 Bourbon ...............11

Office of the Kentucky State Veterinarian
Updated August 25, 2018

Total confirmed cases: 26
College of Agriculture,
Food and Environment
Department of
Veterinary ScienceT

he recent increased incidence of equine
influenza in the United States and abroadnecessitates implementation of prevention andcontrol strategies to protect the health of theequine population. Although vaccination plays
an important role, it should not be relied on as
the sole preventative. Similar to other influenza
viruses, equine influenza virus mutates over timeand vaccines must be periodically updated to keep
current with circulating viruses. Horses that havebeen vaccinated in accordance with manufacturer’slabel instructions and the recommendations ofAmerican Association of Equine Practitioners
may be protected against equine influenza. Studies suggest the use of the modified live intranasal
vaccine in previously unvaccinated horses canprovide protection within five days of primaryadministration. However, no vaccine is 100%
effective. Investigations into recent cases indicatethat vaccinated horses can develop mild clinicalsigns of short duration, whereas unvaccinatedhorses are more severely affected and more likely
to develop secondary pneumonia and pleuritis.
Implementation of biosecurity measures is essential to protecting the health of horses during
influenza season. As influenza virus is spread most
readily through nose-to-nose contact, it is criticalto limit horse-to-horse contact and require strict
isolation of new arrivals and sick horses. Infectedanimals should be kept at a minimum distance of
50 yards from healthy horses.
If no suitable permanent isolation stable is available, then designate an area on the property wherea temporary isolation structure can be erected.
When no appropriate onsite isolation areas are
identified, consider appropriate off-site isolation
facilities such as vacant barns, empty fair or event
grounds, or veterinary clinics. To prevent virustransmission, designate personnel and equipment
to the isolation area. Disposable coveralls, gloves,and boot covers should be used when handlinghorses in isolation. Personnel who must care foranimals both in and outside of isolation should
handle healthy animals first and isolated animals
last. Individuals caring for exposed or infectedhorses should utilize alcohol-based hand sanitizers
after handling all horses.
Influenza virus can be inactivated by exposure
to sunlight or by use of disinfectants. The virus canremain viable for up to 2 days on contaminatedsurfaces, specifically solid surfaces of stall door
latches. Thus, any shared equipment should bethoroughly cleaned and disinfected between uses.
The critical factor in controlling and preventing the spread of influenza virus is monitoring thehealth of all equids. Monitoring includes taking
body temperatures twice daily and recording allclinical observations. Only healthy horses, whichhave been monitored, should be permitted to leave
the premises. Any horse showing clinical signs ofrespiratory disease should be immediately isolated
and examined by a veterinarian. Horses should
remain isolated until they’re clinically healthy andno longer shedding virus. As respiratory sheddingof the influenza virus can persist for 7-10 days postinfection in a naïve animal, horses should remain
isolated for a minimum of 14 days.
Appropriate use of vaccination and implementing biosecurity measures are critical to protecting
the equine industry from highly contagious equine
influenza virus.
CONTACT:
Katie Flynn, BVMS
katherine.flynn@cdfa.ca.gov(916) 900-5039
California Department of Food and Agriculture, Animal
Health Branch
Sacramento, CA

Equine Disease Quarterly Newsletter

5

3. Communicate with your veterinarian and withthe manager or resident veterinarian at any
facility to which you are taking your horse. Is
there an outbreak situation? If so, re-evaluate
your horse’s vaccination status, and re-evaluate
exposing your horse to flu.
4. Biosecurity from infectious diseases is best enforced by avoiding exposure whenever possible.
For farms, the best biosecurity is obtained byquarantining newly arriving horses away fromthe general herd for sufficient time to assurethat the new arrivals are not bringing diseases
with them. EI is transmitted through the air by
coughing and indirectly on hands or clothing/equipment (fomites) that have been in contact
with an infected horse.
CONTACT:
Thomas Chambers, PhD
tmcham1@uky.edu(859) 218-1126
Maxwell H. Gluck Equine Research Center
University of Kentucky
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

APRIL 2019
Volume 28, Number 2

C O M M E N TA RY
KENTUCKY
IN THIS ISSUE

Equine Neorickettsiosis: Incidence in Kentucky in 2018

E

quine neorickettsiosis (EN), more commonly
known as Potomac horse fever, is an equinespecific bacterial disease caused by Neorickettsia
risticii. The disease was first reported in the USA
in 1979 as a sporadic condition observed in horses
pastured in proximity to the Potomac River. Current distribution is now known to extend far beyond the northeastern United States and has beenreported in 43 states in the USA; three provincesin Canada; Uruguay and Brazil in South America;
France and the Netherlands in Europe; and in
India. The disease is often associated with horses
grazing pastures bordering creeks or rivers. Equine
neorickettsiosis is seasonal in occurrence, with the
majority of outbreaks in Kentucky reported in Julythrough September.
The disease is not contagious per se; infection
is naturally acquired by horses accidentally ingesting aquatic insects harboring metacercariae (fluke
larvae) infected with N. risticii.
The life cycle of the bacterium involves operculate freshwater snails and aquatic insects viz
mayflies and caddisflies, the latter being the sourceof infection for horses.
Outbreaks of EN comprise isolated or multiple
cases of the disease on a premises. Experiencehas shown that the disease once confirmed on apremises or in a particular area, tends to recur insubsequent years.

Neorickettsia risticii can cause an acute enterocolitis in susceptible horses that is clinically manifest
by fever, colic of variable severity and profuse
diarrhea. All ages and breeds of horses are at riskof developing the disease. Infections in pregnant
mares can give rise to abortion immediately following infection or months after the resolutionof clinical signs.
Equine neorickettsiosis has been recorded in
Kentucky for a significant number of years. Incidence of the disease can be very variable withincreased case numbers frequently seen in years
with high rainfalls in the spring followed by above
average temperatures in late spring/early summer.
In 2018, the disease was first confirmed in
Kentucky on June 1st. Over the period extending
through the week of 25th August, 26 cases werediagnosed. This figure is probably under-representative of the true incidence of the disease. The
case definition for EN was based on presence ofcharacteristic clinical signs together with a positive
polymerase chain reaction (PCR) test result for thecausal bacterium.
A breakdown of the total number of cases
revealed that the disease was confirmed in ninecounties, the majority in central Kentucky (Figure1). Affected horses ranged from one to 17 yearsof age. The preponderance of cases (20) was seen
in mares. Although the majority of cases were in
Thoroughbreds (18), the disease was recorded in
six other breeds. Of the 26 reported cases in thestate, six died and the remainder survived.

Commentary
International
Fourth Quarter2018  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 2Sarcoids .  .  .  .  .  .  .  .  .  .  .  .  . 3National
Equine Influenza  .  .  .  . 4Kentucky

To minimize losses from EN, horsemen wereencouraged to review the environment in which
they kept their horses and to consult with theirveterinarian on strategies that might be used tomitigate disease risk. Recommendation was also
given to minimize the opportunity for horses toingest aquatic insects by turning off lighting in andaround barns and other areas at nighttime.
CONTACT:
E.S. Rusty Ford
Rusty.ford@ky.gov
Office of the Kentucky State VeterinarianFrankfort, KY

EquineNeorickettsiosis  .  .  .  .  . 5

Figure 1. Potomac Horse Fever Cases in
Kentucky in 2018.

1
1
1 1 4 113 3

1

26 Confirmed Cases:
1 case each.........Bracken, Franklin, Harrison, Shelby, and Metcalfe
3 cases each.......Fayette and Woodford
4 cases .................Scott
11 cases...............Bourbon
Office of the Kentucky State Veterinarian, Updated August 25, 2018

College of Agriculture,
Food and Environment
Department of
Veterinary ScienceT

he recent increased incidence of equine
influenza in the United States and abroadnecessitates implementation of prevention andcontrol strategies to protect the health of theequine population. Although vaccination plays
an important role, it should not be relied on as
the sole preventative. Similar to other influenza
viruses, equine influenza virus mutates over timeand vaccines must be periodically updated to keep
current with circulating viruses. Horses that havebeen vaccinated in accordance with manufacturer’slabel instructions and the recommendations ofAmerican Association of Equine Practitioners
may be protected against equine influenza. Studies suggest the use of the modified live intranasal
vaccine in previously unvaccinated horses canprovide protection within five days of primaryadministration. However, no vaccine is 100%
effective. Investigations into recent cases indicatethat vaccinated horses can develop mild clinicalsigns of short duration, whereas unvaccinatedhorses are more severely affected and more likely
to develop secondary pneumonia and pleuritis.
Implementation of biosecurity measures is essential to protecting the health of horses during
influenza season. As influenza virus is spread most
readily through nose-to-nose contact, it is criticalto limit horse-to-horse contact and require strict
isolation of new arrivals and sick horses. Infectedanimals should be kept at a minimum distance of
50 yards from healthy horses.
If no suitable permanent isolation stable is available, then designate an area on the property wherea temporary isolation structure can be erected.
When no appropriate onsite isolation areas are
identified, consider appropriate off-site isolation
facilities such as vacant barns, empty fair or event
grounds, or veterinary clinics. To prevent virustransmission, designate personnel and equipment
to the isolation area. Disposable coveralls, gloves,and boot covers should be used when handlinghorses in isolation. Personnel who must care foranimals both in and outside of isolation should
handle healthy animals first and isolated animals
last. Individuals caring for exposed or infectedhorses should utilize alcohol-based hand sanitizers
after handling all horses.
Influenza virus can be inactivated by exposure
to sunlight or by use of disinfectants. The virus canremain viable for up to 2 days on contaminatedsurfaces, specifically solid surfaces of stall door
latches. Thus, any shared equipment should bethoroughly cleaned and disinfected between uses.
The critical factor in controlling and preventing the spread of influenza virus is monitoring thehealth of all equids. Monitoring includes taking
body temperatures twice daily and recording allclinical observations. Only healthy horses, whichhave been monitored, should be permitted to leave
the premises. Any horse showing clinical signs ofrespiratory disease should be immediately isolated
and examined by a veterinarian. Horses should
remain isolated until they’re clinically healthy andno longer shedding virus. As respiratory sheddingof the influenza virus can persist for 7-10 days postinfection in a naïve animal, horses should remain
isolated for a minimum of 14 days.
Appropriate use of vaccination and implementing biosecurity measures are critical to protecting
the equine industry from highly contagious equine
influenza virus.
CONTACT:
Katie Flynn, BVMS
katherine.flynn@cdfa.ca.gov(916) 900-5039
California Department of Food and Agriculture, Animal
Health Branch
Sacramento, CA

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

N AT I O N A L

Fourth Quarter 2018

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Equine Disease Quarterly
Editors

Peter Timoney
Alan Loynachan
Cynthia Gaskill

Staff

Diane Furry
Tawana Brown
Dennis Duross
Anita Fleming
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 equine disease outbreaks.
The Republic of South Africa (RSA) reported
isolated cases of African horse sickness in known
infected areas that included the provinces of theEastern Cape, Gauteng, and KwaZulu-Natal.
Occurrence of the disease is as expected for thistime of year.
Equine influenza was recorded in Ecuador (oneoutbreak), France (three outbreaks), and the UK
which considers the disease to be endemic. The disease is also endemic in the USA, being confirmed
in seven states, with some outbreaks characterizedby multiple cases of the disease.
Canada, France, Germany, Ireland, Switzerland,
the UK, and the USA reported multiple outbreaksof strangles. The number of confirmed outbreaks/
cases included two in Canada, 28 in France, fourin Germany, five in Ireland and four in Switzerland. The disease was reported to be endemic
in the UK and in the USA, where 34 outbreaks
were confirmed in 18 states involving at least 68
affected horses.
Equine herpesvirus 1 related diseases wererecorded by France, Germany, Ireland, Japan,
the RSA, the UK, and the USA. Febrile illness
was reported by the RSA and the USA. Respiratory disease was confirmed in France (eight outbreaks), Germany (one outbreak), the RSA (oneoutbreak), and the UK (one outbreak). Abortiondue to EHV-1 was recorded in France (two cases),Germany (single cases on two premises), Ireland(single cases on four premises), Japan (two cases on
separate premises), and the USA (five cases). The
RSA, UK, and USA reported outbreaks of EHV-1
myeloencephalopathy. The RSA and the UK eachreported a single case of the disease, whereas the
USA confirmed four cases involving premises in
Arizona and California.
Equine herpesvirus 4 (EHV-4) respiratory
disease was diagnosed in France (26 outbreaks),
Germany (one outbreak involving four cases ofthe disease), the UK (seven outbreaks), and theUSA (one case). One case of EHV-4 abortion was
confirmed in the USA.

Multiple cases of equine herpesvirus 2 and/or 5
infection were reported by the USA, some associated with evidence of respiratory disease.
France recorded one case of subclinical equine
arteritis virus infection and two cases of abortion
caused by the virus. Germany confirmed the carrierstate in one stallion.
Equine infectious anemia was diagnosed in
Canada (three cases), France (one case), and theUSA (three cases in Colorado and two in Texas).
The RSA and Switzerland reported cases of
equine piroplasmosis. The disease is endemic in the
RSA with cases confirmed in six provinces. One
case of Theileria equi was diagnosed in Switzerland.
Contagious equine metritis was recorded byGermany (two stallions on separate premises)
and South Korea (13 positive venereal swabs from2,236 stallions and broodmares tested as part of anational survey).
The USA confirmed four cases of leptospiralabortion and two cases of equine neorickettsiosis
abortion in Kentucky.
Germany reported one case of salmonellosis(serogroup not specified).
An outbreak of rotaviral enteritis was recorded
by Argentina; a total of ten 2- to 4-month-old
foals were affected on one premises, all of which
had been vaccinated.
The USA reported eight cases of infection with
Lawsonia intracellularis in Kentucky.
The fourth quarter of 2018 saw a sharp decline
in the number of cases of Eastern equine encephalomyelitis confirmed in the USA, with only threecases recorded, all in New York State.
West Nile virus activity was reported in Canada(3 cases), France (3 case), Portugal (1 case), Tunisia(7 cases), Turkey (1 case), and the USA (70 cases).
Rhodococcal-related disease is endemic in theUSA. Even though only three outbreaks were recorded in the fourth quarter, this is not reflectiveof the true incidence of the disease.
Singapore confirmed one case of Old world
screwworm infection in a horse, and Switzerland
reported more than four cases of Atypical Myopathy during October 2018.

Sarcoids

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arcoids are believed to be the most common
skin tumor of the horse and affect about
2% of horses worldwide. Although they do notmetastasize (spread to distant locations), they
undoubtedly cause welfare concerns, especiallyin the ulcerated “fibroblastic” form. This may bethrough discomfort from the lesions themselves,from fly interference with the lesions, and also
from administered treatments. In their most extreme forms, they can affect eyelid function andlead to secondary ulceration of the eye’s surface(Figure 1). Clearly, they are not a “benign” lesion, despite their benign classification, and theyshould never be ignored. The presence of sarcoids
also has financial implications not only due to the(sometimes very high) cost of treatment, but also
due to reduced resale value.
There is compelling evidence that sarcoids arecaused by a bovine papillomavirus which is believed to be transmitted by flies, most likely from
infected cattle, but possibly also from infectedhorses. It remains unclear exactly how the virus
leads to neoplastic (cancerous) change, or why
the virus is able to cause disease in more than one
species. Interestingly, a (human) papillomavirus
also is responsible for the vast majority of cases ofcervical cancer and an increasingly large proportionof tumors of the head and neck in humans; clearly
there is much to be learned about the implicationsof infection with papillomaviruses in all species.
There is little doubt that there is a heritablecomponent to the disease. In warmbloods, theheritability has been well demonstrated: Breeding
two sarcoid-affected horses vastly increases therisk of producing a horse that develops sarcoids atsome stage in its life. There also appear to be breedrelated differences in sarcoid risk: Thoroughbreds
are more likely to develop sarcoids than Standardbreds, and Lipizzaners seem more resistant tosarcoid development. Unlike melanomas, there isno color predisposition and gender doesn’t affectthe chance of developing the disease. Specific genevariations, noted in horses with sarcoids, are also
associated with virally induced cancers in humans.
The reasons for this association are unclear, but it islikely due to differences in immune function andmay explain the apparent breed-specific variationin sarcoid risk.
Treatment options for sarcoids are numerous,
with no one option being suitable for every case.
Traditionally, sarcoids were often left without treatment, but as they almost invariably become larger
and more difficult to treat, early intervention isstrongly recommended to avoid long-term sequelae. Treatment may involve topical or intra-lesional
chemotherapy or immune modulators, surgicalprocedures, or radiotherapy. Electrochemotherapy
is a relatively new alternative treatment option withapparently very good results, but it unfortunately
necessitates the use of multiple general anaesthetics, so the risks must be carefully considered.
Appropriate treatment selection is largely dictated by the location and type of the lesion (Figure2). Laser surgical excision is the author’s treatmentof choice for the majority of lesions in locations
other than around the eye; periocular lesions
are treated via radiotherapy with great success.
Reported success rates for laser surgical excision
are in the order of 83% and for radiotherapy arearound 90%; compared to other treatment options
they represent the least risk to the horse and leadto the best results. However, not every lesion—or
horse—is a suitable candidate for these treatments,
and the key is to select the method most likely
to be successful in the first instance. Recurrent
sarcoids become increasingly difficult to manage
and convey a far worse prognosis than those appropriately treated in the first place.
CONTACT:
Anna Hollis, BVetMed DACVIM DipECEIM MRCVS
anna.hollis@aht.org.uk
Animal Health Trust
Newmarket, UK

Equine Influenza

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Figure 1.
Horse with sarcoid lesion
before treatment.

Figure 2.
Horse 2½ years after
treatment.

quine influenza (EI) is considered endemic
in both the USA and Europe, but the viruses
causing EI differ slightly. For many years, the viruses in circulation in the USA have been ‘Florida
clade 1’ (FC1) whereas in Europe they have been
‘Florida clade 2’ (FC2). These clades split apart in
2003; circulation of FC2 ceased in the USA around2005, and by 2010 there was no evidence of FC1
in circulation in Europe. Because of the extensive
movement of horses between North America andEurope, the international panel of EI experts hasrecommended for the last ten years that EI vaccines contain representatives of both FC1 andFC2. Some (not all) available EI vaccines meetthis recommendation.
EI virus activity has recently increased in theUSA, Europe, and Nigeria. Normally, the virus
circulates at a variable, but fairly low, level in theUSA, but virus activity surged in the last threemonths of 2018 with outbreaks in 12 states. An
extensive EI event occurred in a donkey sanctuary
in Nigeria. For the first time since 2015, multiple
outbreaks of EI were reported during January andFebruary of 2019 in France, Belgium, the Netherlands, Germany, Ireland, England, and Scotland.
In England, it resulted in a temporary lockdownof at least 174 premises and cancellation of racing for 6 days in February. Outbreaks were also
reported in California, Arizona, Ohio, Indiana,
and Washington State.
Some of the horses in these outbreaks, in boththe USA and Europe, had been vaccinated for EI,
raising the question: Is this a new strain that is notin the vaccines? The answer appears to be no. While
the virus causing the Nigerian EI event is stilluncharacterized, genetic analysis of isolates fromboth England and the USA confirms these as FC1.
There are two mutations that make them different
from the recommended vaccines strains, but arethese important? That is still under investigation.
The absence of FC1 from European circulationmeans their horses have no natural immunity andare dependent on vaccination for protection. The
reports from England indicate that the clinicaldisease is of shorter duration and less severe invaccinated horses; this would indicate the vaccines
are working, at least partially. Milder disease invaccinated horses may reflect an inadequate level ofprotective immunity following exposure to unvaccinated horses shedding large quantities of virus.
What should owners and veterinarians do toprotect their horses from EI?
1. Familiarize yourself with the clinical signs of EI.
Often the very first sign is a harsh cough. Othersigns include fever and nasal discharge, which
is usually watery (serous) at first and then turns
thick and yellow (mucopurulent). The horse
may show unusually rapid breathing (tachypnea) or lose its appetite (anorexia). Sometimes
there may be enlarged submandibular lymph
nodes or dependent limb edema. Keep inmind that not all these signs may be present.
Horses can be infected and still appear normal(subclinical infection), especially if they havebeen previously vaccinated. Other infectious
agents can produce clinical signs that look like
EI, but aren’t. EHV-1/4 or strangles (Streptococcus equi) are examples. Have your veterinariancollect a nasal swab, or ideally a nasopharyngeal
swab (which goes beyond the nostrils into theback of the throat), and send it to a veterinary
diagnostic laboratory to confirm a diagnosis.
Information on nasal-swabbing can be found at
http://vetsci.ca.uky.edu/services. If your horse
does develop clinical signs of EI, then the ruleof thumb is that for every day of fever, it should
be stall-rested for a week.
2. Vaccinate your horses using a vaccine that
protects against both FC1 and FC2 viruses.
Horses’ antibody responses to vaccination do
not last indefinitely, so if your horse has notbeen vaccinated for six months or more, then it
is due for a booster. If it has been three months
or less since the last booster, then hopefully
your horse’s immunity should be at its peak.
Consult your veterinarian and refer to the
AAEP Guidelines (https://aaep.org/guidelines/
vaccination-guidelines/risk-based-vaccinationguidelines/equine-influenza). In the event of an
EI outbreak, where your horse may potentiallybe exposed, vaccination in the immediate faceof the event might help if there is sufficienttime—at least a week—for the horse’s immune
system to start making antibodies.