Equine viral arteritis (EVA) is a contagious disease of horses caused by equine arteritis virus (EAV), an RNA virus that is found in horse populations in many countries. While typically not life-threatening to otherwise healthy adult horses, EAV can cause abortion in pregnant mares; uncommonly, death in young foals; and establish a long-term carrier state in breeding stallions. While various horse breeds appear equally susceptible to EAV, the prevalence of infection can vary widely, with higher sero-positivity rates occurring in Standardbreds and Warmbloods.
Clinical signs, if they occur, typically develop 3 to 7 days post-infection and are variable but may include any combination or all of the following:
Abortion is a frequent sequel to infection in the unprotected, pregnant mare. When pregnant mares are exposed to the virus very close to term, they may not abort but give birth to a congenitally infected foal, affected with a rapidly progressive interstitial pneumonia. Foals within a few months of age, if exposed to EAV can develop a life-threatening pneumonia or pneumoenteritis.
How it’s spread
Much like a human would contract a respiratory virus infection, like a cold or flu, horses can contract EAV infection from acutely affected horses. In addition, stallions can shed the virus in their semen. The respiratory route is the primary means whereby the virus is spread during outbreaks of EVA at racetracks, horse shows, sales and veterinary clinics. Venereal transmission, in contrast, has frequently been associated with the primary spread of EAV on breeding farms. As a result, every precaution should be taken with EAV positive semen to ensure that outbreaks do not occur.
Equine Arteritis Virus is a very manageable disease. Vaccination against the disease is a first line of defense, particularly of colts between the ages of six and nine months in breeds in which EAV is endemic, e.g. the Standardbred. Over a number of years, this would significantly reduce the number of carrier stallions.
ARVAC is one of the only vaccines available to prevent Equine Viral Arteritis. It should be used to help prevent any carrier stallions, this way it is not passed down the bloodline. Also, it is strongly recommended that mares be vaccinated against EVA at least three weeks before insemination. The reasons for this are twofold: first, vaccinated animals need to be provided with adequate opportunity to mount an immune response to the virus; second, first-time vaccinated animals may shed small amounts of vaccine virus for a short interval after vaccination, during which time they should be isolated from other horses negative for antibodies to the virus. This vaccine has been tested and shown to be satisfactory for marketing in accordance with procedures required by the U.S. Department of Agriculture.