Understanding EVA

What you need to know about equine viral arteritis.

Although not life-threatening to most healthy adult horses, infection with equine arteritis virus can result in abortion in pregnant mares and death in young foals, and can render breeding stallions permanent carriers of the virus. Luckily, EVA is manageable. Equine arteritis virus, first isolated in 1953, has sporadically affected the equine breeding industry in Europe and North America. Described by the U.S. Department of Agriculture as an acute, contagious viral disease of the respiratory tract, EVA is transmitted by the airborne route or by venereal contact (natural cover or artificial insemination). Reported incidence of the disease has increased during the past 15-20 years, due in part to the more widespread use of artificial insemination. The virus shows no prejudice among equine breeds and can be disseminated on breeding farms, racetracks, sales and horse shows where horses are closely congregated.

According to the American Association of Equine Practitioners, the clinical signs of EVA include fever, depression, edema, loss of appetite, nasal discharge, conjunctivitis, skin rash and swelling above or around the eyes, limbs and genitals. Most horses that contract the disease make full and uneventful recoveries. The most economically damaging consequences of infection include the birth of weak or sick foals and abortion in mares. What is seldom realized is that many infected horses develop no signs of EVA; in other words, they are not apparently infected with the virus. However, AAEP is quick to point out that any infected horse can spread the virus and quickly affect a group of susceptible horses. Rapid spread among pregnant mares can easily wipe out a foal crop.

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Clinical signs of EVA mimic those of several other equine diseases such as equine rhinopneumonitis, influenza, equine infectious anemia and purpura hemorrhagica, so it's critical to test for EVA as soon as possible. Confirmation of a provisional clinical diagnosis of EVA is possible only by laboratory testing of nasal secretions, blood, semen, fetal and placental tissues and fluids. When a horse is exposed to equine arteritis virus, signs of illness might develop within three to seven days, depending on the route of exposure. If a horse is diagnosed with EVA, treatment is directed at reducing the severity of its clinical signs. A veterinarian might prescribe nonsteroidal anti-inflammatory drugs to make the horse more comfortable if it experiences severe fever or swelling.

The Good News

AAEP is adamant that EVA is controllable and preventable. Researchers have determined the cause and how the virus is spread, and vaccination is available The USDA has the following tips for dealing with an EVA outbreak:

  1. Isolate affected horses as soon as possible.
  2. Notify your veterinarian immediately.
  3. In consultation with your vet, have the diagnosis of EVA confirmed by a qualified laboratory.
  4. If a mare has aborted, place the fetus and placenta in a leak-proof bag, refrigerate and send to the nearest appropriate laboratory for testing.
  5. Disinfect the stall, equipment and facilities using a phenolic disinfectant as advised by your veterinarian. After treatment with disinfectant, dispose of bedding by composting in an area away from horses.
  6. Wash down the mare's hindquarters and tail with an antiseptic solution as advised by your veterinarian, and keep her separated from other horses for at least three weeks.
  7. Restrict the movement of all horses to and from the farm or ranch as advised by your veterinarian.
  8. Suspend breeding operations until the outbreak is over. Notify mare owners.
  9. Vaccinate all at-risk horses as advised by your veterinarian.
  10. Notify your state veterinarian or appropriate state regulatory agency of the outbreak.

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Routes of EVA Transmission

Much like humans contract colds and flu viruses, horses can contract equine arteritis virus infection from acutely infected horses. Respiratory - an acutely infected horse spreads the virus to other horses via its respiratory secretions. Venereal -- virus shed in the semen of an infected stallion is transmitted to mares when they are bred. Indirect contamination - tack and equipment shared among horses can serve as a source of infection. In utero - virus passes across the placenta from an infected mare to her unborn foal.

Minimize the Risk:

  • Test stallions for the virus before they are used for breeding. Alert mare owners of a stallion's carrier status.
  • Immunize susceptible stallion populations.
  • Vaccinate sexually immature colts between 6 and 9 months of age to lessen their risk of becoming carriers.
  • Follow recommended vaccination guidelines for your mare.