Equine Viral Arteritis (EVA) is a contagious viral disease that causes pregnancy failure (spontaneous abortions) in the mare. In addition to affecting pregnancy, EVA causes flu-like symptoms. Therefore, it spreads via coughing or sneezing (respiratory means) as well as through reproductive activities. Because horses communicate by rubbing faces and snorting/inhaling breath, it can spread easily during transport, at horse shows, racetracks, or any other situation where horses are in close contact.
First documented in Europe approximately one hundred years ago, EVA spread to the United States in the 1950s and major outbreaks have occurred in Kentucky and other states. The most recent outbreak occurred June 2006 in New Mexico. Outbreaks may be reported to the EVA Reference Laboratory, c/o Gluck Equine Research Center at the University of Kentucky (tel. 859.257.4757) which collects blood samples from infected horses for purposes of research.
Like most viruses, a colt, filly, gelding or mare not in foal may come in contact with the disease and naturally shed off the virus, avoiding illness and developing immunity against it. However, stallions that become infected typically become viral carriers for many years and will infect any mare in season with which they have contact. Humans and other domestic animals are not at risk for EVA. The disease is most widespread amongst Standardbred horses.
Diagnosis should be made by having your vet send blood samples for testing. Any mare that has respiratory illness along with abortion is a good indicator for the disease. Other signs are coughing, anemia, fever, muscle soreness, skin rash, nasal discharge, genital swelling, and eye swelling, redness or discharge.
Death from EVA in adult horses is rare. Although there is no known cure for the disease, rest, seclusion from uninfected horses, and antibiotics are typical treatments. Mares that contract EVA will eventually recover; however, any stallion that has had EVA should not be bred.
Unfortunately, once a stallion is affected, blood tests can show no sign of the disease, however, the virus will still be present in the semen. It is particularly difficult to pin down infected animals because a virus-shedding stallion can show no sign of illness yet can still pass the disease along to mares via semen alone, even when no other contact with the mare has been made. Therefore, before purchasing semen, inquire whether the stallion has been vaccinated since birth, and yearly, against EVA.
The good news is that complete prevention is possible via vaccination. Colts and fillies should be vaccinated between six and nine months of age. The vaccine cannot be used in pregnant mares. Considering the devastating effects EVA can cause, and the ease with which it spreads, it is worthwhile to request your vet to include the EVA vaccine in your horse’s vaccination schedule. Yearly boosters are required.
