EVA was detected in New Mexico and Utah in 2006. It is a virus that causes a mild to severe respiratory disease in horses. This virus can also cause mares to abort their foals. Some stallions that are infected with the virus will become carriers, shedding the virus in their semen. Signs of the disease include fever, depression, diarrhea, nasal discharge, coughing, and swelling of the head, body or legs. If you suspect your horse has EVA, a blood sample can be sent to the lab by your veterinarian to confirm the disease. Many diseases have similar symptoms. Horses can contract the virus by inhalation, such as nose to nose contact. The virus can contaminate bedding and other objects, but does not live well outside the horse. An infected stallion can shed the virus in his semen, even if it is extended and cooled. Most affected mares, geldings, and sexually immature stallions will eliminate the virus after a brief period of illness. The big problem is created when a breeding stallion is infected with the virus. He can become a carrier of the disease and shed the virus for long periods of time. Mares must be vaccinated in order to be bred to an EVA positive stallion.
If you are breeding your mare this year, contact the breeding farm to see if they require a negative EVA test before arrival at the farm. A vaccine is available for equine viral arteritis. The vaccine has been on the market for years, used mostly by the warmblood community. The high demand by the quarter horse breeders this year has caused the vaccine to be on manufacture back order until mid-march. After vaccination, the horses need to be separated from unvaccinated horses for 10 days. Stallions should not be bred for 28 days following vaccination, and mares should not be bred for 21 days after vaccination. Vaccinated horses must also be kept away from pregnant mares for at least 28 days. Vaccinated mares that are bred to carrier stallions should be isolated from other non-vaccinated horses for 21 days after they are bred.
Owners that are considering vaccinating their mares should also check other state and international requirements. Some countries may not allow vaccinated horses to be imported. If you do vaccinate, it is a good idea to test the horse before the vaccine is given. Wait until you get these test results back before you vaccinate. Once the test results come back negative, draw several tubes of blood from the horse the same day that you vaccinate him. Send one of these tubes off to the lab to prove that the horse was negative to EVA the day he was vaccinated. Keep the other tubes in the refrigerator in case the first tube is lost or broken. Vaccinated horses will test positive for the disease. Know the EVA status of any stallion semen that you have shipped to you. Consult with your veterinarian to find out if vaccination is a good idea for your horse.