What Is a Coggins Test?

The Coggins test is named for Leroy Coggins, the veterinarian who developed the test to detect antibodies against equine infectious anemia virus (EIA) in 1970. There are other approved tests, but the Coggins test remains the most definitive test for EIA.

Once infected with EIA, a horse remains infected for life. Infections in horses are rare and incurable, and there is no available vaccine. The EIA virus is a member of the same family as human immunodeficiency virus. Only a few horses per 10,000 are infected in the United States. Most cases occur in states along the Mississippi River or in the southeast.

The EIA virus is spread through the blood of infected horses, primarily by large biting insects such as horseflies and deerflies. Virus spread can also occur through blood-contaminated needles or surgical instruments. There have been some cases of EIA when blood products, such as plasma, were obtained from an infected horse and administered to others.

Clinical signs of EIA include fever, lethargy, edema, and not eating. Some infected horses may die, but most will become chronic asymptomatic carriers of the virus. Asymptomatic carriers recover and show no clinical signs of EIA unless the virus mutates or the horse becomes immunosuppressed. The horse will develop active clinical signs again and the numbers of virus in the horse’s blood greatly increase. Asymptomatic carriers are the reservoir of EIA infection because they remain infected for life and may periodically have sufficient viral loads in their blood to infect other horses if they are bitten by horseflies or deerflies and those flies feed on another horse.

Negative Coggins tests are required for certificates of veterinary inspection and whenever horses are comingled, such as at racetracks, shows, and trail rides to prevent the possible spread of EIA.