Equine Viral Arteritis (EVA) is a contagious viral disease in horses caused by Equine Arteritis Virus (EAV). Infection can go undetected by horse owners/breeders and in herds that were previously unexposed (naïve). Abortion rates in pregnant mares can reach up to 70%. Most horses infected with EAV will show minimal, if any, clinical signs and recover without incident; although, stallions can become carriers and lifelong shedders of the virus. There is a vaccine available that has been shown to prevent infection with EAV. Vaccination should be performed at least 21 days prior to the start of breeding season to provide adequate levels of immunity. EAV has not been shown to be zoonotic.


During the spring of 1984, a virus identified as Equine Arteritis Virus, by the University of Kentucky's Department of Veterinary Science, was threatening Kentucky's thoroughbred population. As a result of the continued spread of the virus amongst Central Kentucky's thoroughbred farms, all breeding of thoroughbred horses was ordered stopped during the early summer months by the Kentucky Department of Agriculture.

The Department of Agriculture, working cooperatively with the University of Kentucky's Department of Veterinary Science, worked throughout the fall and winter to determine the extent of the recent outbreak. Prior to the 1985 breeding season, all thoroughbred stallions were tested under the supervision of the Department. All stallions found to be positive to the serology test were quarantined while additional testing was conducted to determine if they in fact were carriers of the arteritis virus.

After a short delay, non-affected stallions were permitted to begin breeding in 1985. Stallions which were not vaccinated against the virus were monitored by serology testing every 14 days throughout the course of the breeding season to ensure that the virus was not being spread. Stallions which were found to be shedding arteritis virus were permitted to return to breeding midway through the '85 breeding season. These stallions were heavily regulated by the Department of Agriculture to ensure that they were bred only to qualified mares which were approved to be bred by the Office of State Veterinarian while following a stringent post breeding protocol consisting of isolation and quarantine.

Today, there are no known thoroughbred shedding stallions standing at stud in Kentucky. The Department of Agriculture requires that all thoroughbred stallions standing at stud in Kentucky be vaccinated annually against Equine Arteritis Virus. Stallions which are standing their first season in Kentucky are required to be tested prior to vaccination in order to determine that they are not affected with the arteritis virus. As of today, the only commercially approved vaccine for use is manufactured by Fort Dodge Laboratories and is called ARVAC. 

The Kentucky Department of Agriculture, working cooperatively with the Jockey Club, maintains a stallion roster to ensure that all stallions standing in Kentucky are properly vaccinated.

Click here for Kentucky's EVA Regulation


Click to view Kentucky Department of Agriculture Equine Viral Arteritis Thoroughbred Stallions