Viral Arteritis in Horses

October 25, 2010 (published) | August 21, 2017 (revised)

Equine viral arteritis, or EVA, is a contagious disease of horses caused by a virus. Although not deadly, it can cause abortion in pregnant mares, death in young foals, and can become a persistent carrier in stallions. And although Standardbreds and warmbloods are the most common horses affected, we did have a quarter horse outbreak in six states in 2006 that concerned horse breeders. Transmission commonly occurs through direct contact with horses spreading the virus in their respiratory tract, but venereal transmission is a major concern on breeding farms as the virus can even be spread through chilled or frozen semen.

Clinical signs of EVA infection include fever, depression, decreased appetite, swelling of the lower legs, scrotum and mammary area, hives, inflammation around the eyes, and sometimes nasal discharge. If a pregnant mare is exposed close to term, she may not abort but may have an infected foal who may develop a serious case of pneumonia. Foals also infected within a few months after being born can develop a severe pneumonia or intestinal infection. Colts and stallions can become life-long carriers of the virus.

There is an EVA vaccine for horses that is safe and effective. However, since the vaccine can cause horses to test positive for the virus and it is impossible to determine if the horse is positive from vaccine or infection, all horses should be tested before being vaccinated. There is a lot of technical aspects as far as timing of vaccination depending on age and use of the horse, so careful consideration should be used before vaccinating your horses for EVA. Discuss the issues with your veterinarian.

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