COOPERATIVE EXTENSION SERVICE • UNIVERSITY OF KENTUCKY COLLEGE OF AGRICULTURE, LEXINGTON, KY, 40546 ID-197 Equine Viral Arteritis Fernanda C. Camargo and K. Amy Lawyer, Animal and Food Sciences, and Peter Timoney, Veterinary Sciences

quine viral arteritis (EVA) is a con- Additionally, EAV can be spread cooled, and frozen semen for varying pe- tagious disease of and other through indirect contact with objects riods of time—years in the case of frozen Eequine species caused by equine arteritis contaminated with in urine or other semen. Once mares are infected with virus (EAV) that is found in popula- body secretions/excretions of acutely EAV, they can then transmit the virus to tions in many countries. It was first iso- infected horses, aborted fetuses, and pla- other horses, primarily via the respiratory lated and identified in 1953 from the lung cental membranes and fluids. Exposure route but also venereally, for 6-10 days. of an aborted fetus with characteristic in such instances is by the respiratory pathologic changes in the smaller arter- route. There is evidence that EAV can Development of the Disease ies, which is how the disease got its name. also be transmitted via embryo transfer. After respiratory exposure, EAV rap- EVA was differentiated from influenza The prevalence of EAV infection— idly spreads from the lungs to the regional and equine rhinopneumonitis caused that is, frequency of EAV antibodies in bronchial lymph nodes, where it multi- by equine herpesviruses 1 and 4, both a group or population of horses—varies plies and is released into the bloodstream of which can cause clinically similar from country to country and from breed and lymphatics. The virus is dispersed respiratory disease in horses. Although to breed. Higher seropositivity rates often throughout the body principally by way the majority of cases of primary infec- occur in Standardbreds and . of a cell-associated viremia. In the vast tion with EAV are asymptomatic, the EAV infection is considered endemic majority of cases, EAV is cleared from the virus can cause signs of respiratory and in Standardbreds in the United States, body fluids and tissues of infected horses systemic illness, abortion in pregnant with up to 85% of adult Standardbreds within 28 days, the exception being the mares, and infrequently, life-threatening frequently being seropositive to the virus. carrier . The vascular lesions start respiratory or enteric illness in young The seroprevalence of EAV infection in to diminish after 10-12 days and resolve foals. A significant outcome of EAV and mares in some completely in a matter of a few weeks. infection in the sexually mature colt or European countries can be very high, stallion is establishment of a long-term with up to 93% of Austrian Warmblood Clinical Outcome carrier state in a variable percentage of stallions found antibody positive in one If clinical signs occur, they develop infected animals. study. within 3-13 days after exposure, normally An extensive outbreak of EVA on a Persistently infected carrier stallions a week if is via the venereal large number of breeding are the primary natural reservoir of EAV route. farms in Kentucky in 1984 resulted in and are majorly responsible for perpetu- Acutely infected animals may present widespread national and international ating and maintaining the virus in equine any or all of the following signs: concerns over the disease. That was populations. Equine arteritis virus is • fever, loss of appetite, depression, lym- the first occasion of EVA diagnosis in restricted to the reproductive tract in phocytopenia in North America. The the carrier stallion, where it persists in • dependent edema or fluid accumula- occurrence led to major restrictions be- certain of the accessory sex glands. Long tion in and swelling of limbs, scrotum, ing placed on movement of horses from after the animal has recovered from the sheath, and mammary glands the United States, many of which are still acute phase of the infection, virus con- • respiratory signs, including nasal and/ in place today. tinues to be shed, sometimes for many or ocular discharge years, in the semen of such stallions. Transmission • conjunctivitis or “pink-eye” Studies have shown that persistence of • skin rash Equine arteritis virus is most fre- EAV is a testosterone-dependent carrier • abortion in the pregnant mare quently transmitted by direct physical state. Neither mares, geldings, nor sexu- • interstitial pneumonia and enteritis in contact with acutely infected horses via ally immature colts can become carriers young foals virus-containing secretions or excretions. of the virus. • persistent infection in the stallion Transmission can also occur through When mares without detectable anti- breeding mares naturally or by artifi- bodies to the virus are bred to a carrier Some clinical signs are pictured in cial insemination with the semen of an stallion, the transmission rate can be as Figure 1. acutely or chronically infected stallion. high as 85-100%. Bred mares will sero- convert (produce EAV antibodies) within 7-28 days. EAV can remain viable in fresh,

Agriculture and Natural Resources • Family and Consumer Sciences • 4-H Youth Development • Community and Economic Development EXTENSION Treatment Figure 1. Signs of EAV infection. No specific anti-viral treatment currently exists for this disease. Non- steroidal anti-inflammatories are recom- mended in severe clinical cases of EVA to reduce the severity of illness. These non-steroidal anti-inflammatories are especially indicated in affected stallions to minimize the chances of a period of temporary sub-fertility that can last for up to four months. The vast majority of horses that develop EVA will experience Depression Swelling of scrotum a full and uneventful recovery with no adverse side effects, even without the intervention of any symptomatic treat- ment. Diagnosis EVA cannot be diagnosed on clinical signs alone, as these signs can closely resemble those of a wide range of other infectious and non-infectious equine Swelling of limbs diseases. Laboratory confirmation of a provisional clinical diagnosis is required. Diagnosis of the carrier state in the stallion is based upon detection of the virus in the semen. Carrier stallions are constant shedders of EAV in semen but Skin rash, urticaria, or not in any other secretion or excretion. Currently, it is not possible to dif- ferentiate a -induced antibody response from that due to natural infec- tion. Swelling of eyes and conjunctivitis Economic Significance of EVA EVA can economically impact both the breeding and performance sectors of the equine industry. Direct financial losses resulting from outbreaks on breed- ing farms include the following: • loss of foals (abortion or death) • decreased commercial value of persis- tently infected stallions • reduced demand to breed to carrier Ocular discharge and swelling of eyes Swelling of mammary glands stallions because of the expense and inconvenience involved in vaccinating and isolating the mares before and after Prevention • protect stallions against development breeding of the carrier state EVA is a preventable and controllable • reduced export markets for horses that • immunize seronegative mares before disease. Integral to the success of current are seropositive they are bred to an EAV-infected stal- control programs against EVA is the lion or with EAV-infective semen availability of a safe and effective vaccine An EVA outbreak at the racetrack • prevention and control of outbreaks in against the disease. or show grounds has the potential for non-breeding populations widespread transmission and financial Vaccination will: losses as a result of disruption of training • provide clinical protection against schedules, reduced race or show entries, EVA, especially in the face of a field or even cancellation of horse-related outbreak of the disease events. Prevention involves minimizing or The following are some management Resources eliminating direct or indirect contact of measures that can help you prevent or United States Department of Agriculture susceptible horses with various secre- minimize the spread of EAV: (USDA): http://www.aphis.usda.gov/ tions, excretions, or tissues of infected • Ideally, isolate all new horses and those animal_health/animal_diseases/eva/ horses together with a strategic vaccina- returning from other farms, sales, or Balasuriya, U.B.R., MacLachlan, N.J. tion program of stallions and sexually racetracks for three to four weeks. Equine Viral Arteritis. In: Equine Infec- mature colts to prevent establishment • Segregate pregnant mares from other tious Diseases. Editors: Debra C. Sellon of the carrier state. Discuss with your horses on the farm and maintain these and Maureen Long, Saunders-Elsevier, veterinarian about the need to vaccinate mares in small groups until they have Missouri, USA, pp. 153-164, 2007. your breeding and performance horses. foaled, which makes it easier to contain Timoney, P.J. and McCollum, W.H. Equine Current control programs focus pri- an outbreak should it occur. Viral Arteritis. In: The Veterinary Clin- marily on: • Breeding farm operations should ics of North America: Equine Practice • restricting spread of the virus in breed- blood-test all new breeding stallions on Infectious Diseases. Editor: Josie ing horse populations to prevent out- for the presence of antibodies to EAV L. Traub-Dargatz, W.B. Saunders, breaks of EAV-related abortion and/or before each breeding season and if Philadelphia, Pennsylvania, USA, pp. illness and death in very young foals found seropositive, confirm that their 295-309, 1993. • minimizing risk of establishing the semen is negative for virus. Timoney, P.J. Equine Viral Arteritis. In: carrier state in stallions • When planning to breed your mare, Equine Respiratory Diseases. Editor: make sure the stallion is either a non- P. Lekeux, International Veterinary Nationally, no ongoing programs exist carrier or has been vaccinated against Information Service ( ), for preventing introduction of EAV or EVA. www.ivis.org Ithaca, New York, USA, 2002. curtailing its spread among performance • Annually vaccinate all non-carrier horses at racetracks, equestrian events, or breeding stallions at least four weeks horse shows. The infrequency with which before the start of each breeding sea- such disease events occur is not sufficient son. justification for such a program. Horses • If you intend to breed a seronegative travelling internationally, however, mare to a carrier stallion, vaccinate the need to be confirmed that they are not mare at least 21 days before breeding . shedding the virus. They also need to be Mares do not have to be revaccinated either seronegative or, if seropositive, be if they are to be rebred to the same or accompanied by certification that their another carrier stallion. serum antibody level is either stable or • Isolate first-time vaccinated mares bred decreasing. Semen being exported needs to a carrier stallion from all but known to be accompanied by laboratory certifi- seropositive horses for three weeks. It is cation that it is negative for EAV. especially important to avoid any con- tact between these mares and pregnant mares to which they could spread the virus by the respiratory route.

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