The Oklahoma Department of Agriculture, Animal Industry Services works with horse owners throughout the state to protect our equine population (there are an estimated 278,000 horses in our state) from the introduction of disease and to insure that they are able to move interstate and internationally.
Oklahoma has facilities approved to complete the testing and quarantine required for animals that are exported internationally. In 2000, 659 Oklahoma horses were exported to 15 different countries including South America, Asia, all of Europe, Mexico, Canada and Japan. Oklahoma Department of Agriculture's disease monitoring and control programs insures that these horse owners continue to be able to import and export their animals.
Equine Viral Arteritis (EVA) is a reportable disease in Oklahoma. While EVA is typically not life-threatening to otherwise healthy adult horses, EVA is of special concern to horse breeders because it can cause abortion in pregnant mares, death in young foals, and breeding stallions may become permanent carriers of the virus. The increase in international trade of horses and semen for artificial insemination has increased the risk of passing equine arteritis virus from one equine population to another. In 1984, there was an EVA epidemic in America's Thoroughbred industry, which led major restrictions by the international community on the movement of horses from the United States.
Many horses exposed to equine arteritis virus will develop no signs of the disease. If illness does occur, usually within 3 to 7 days of exposure, diagnosis can be difficult because EVA is clinically similar to several other equine diseases such as Equine Rhinopneumonitis, Influenza, Equine Infectious Anemia (EIA) and Purpura Hemmorrhagica. Clinical signs vary in severity and can last from 2 to 14 days. They include:
- Swelling, primarily of legs, scrotum, sheath, or mammary glands.
- Loss of appetite
- Conjunctivitis (inflammation, discharge, and swelling around the eyes)
- Nasal discharge
- Skin rash (frequently localized on the head and neck)
- Abortion in pregnant mares
- Pneumonia and death in young foals.
Laboratory testing is necessary to diagnose EVA, a blood test to screen for the presence of antibodies to the virus is the most commonly used test. Equine arteritis virus can be transmitted among horses in several ways:
- Respiratory-an acutely infected horse spreads the virus via respiratory secretions (this type of transmission commonly occurs at shows, sales, and racetracks)
- Venereal-the virus is shed in the semen of an infected stallion and is transmitted when mares are bred.
- Indirect contamination-tack or equipment shared among horses may serve as an infection source.
- In utero-the virus passed across the placenta from an infected mare to her unborn foal.
Some stallions infected with equine arteritis virus may become permanent carriers of the virus. Stallions may show no clinical signs of the disease, yet the virus remains in the reproductive tract indefinitely. The virus may be passed to mares via the semen when they are bred, whether through live cover or artificial insemination.
The good news about EVA is that it can be controlled. Infection with equine arteritis virus stimulates a very strong and probably lifelong immunity. A vaccine is available that also produces immunity, however this immunity leads to a positive antibody test result which may make horses ineligible for export to some countries.
Sound management practices can help prevent and control EVA:
- Isolate all new arrivals (and returning horses) to your farm for 3 to 4 weeks.
- If possible, segregate pregnant mares from other horses.
- Blood test all breeding stallions for equine arteritis virus antibodies.
- Check semen of any unvaccinated, antibody positive stallions to identify carriers before breeding.
- Vaccinate all non-carrier breeding stallions annually at least 4 weeks before the start of each breeding season (remember that the positive test resulting from vaccination may present a problem with international export).
- Maintain any equine arteritis virus carrier stallions in isolation.
- Restrict breeding equine arteritis virus carrier stallions to vaccinated mares or mares which test positive for n aturally acquired antibodies to the virus.
- Vaccinate mares against EVA at least 3 weeks prior to breeding to a known carrier stallion.
- Isolate mares vaccinated for the first time against EVA for 3 weeks following breeding to an equine arteritis virus carrier stallion (there is no need to revaccinate mares for rebreeding).
- In breeds or areas with high rates of EVA infection, vaccinate all intact males between 6 and 12 months of age as advised by your veterinarian.
For additional information on this or other equine diseases, contact the Oklahoma Department of Agriculture, Animal Industry Services at (405) 522-6124.
The Oklahoma Horse Industry Council is a non-profit grass roots organization representing the entire horse industry from recreational horse owners to professional horsemen, embracing all activities, disciplines, and breeds.