by Robert N. Oglesby, DVM

Equine Infectious Anemia is a viral disease for which there is no vaccine and no cure. Though most horses succumb rapidly to EIA a percentage of infected horses appear to recover. However they still harbor the virus and during times of stress may become ill again. It is because of these healthy appearing carriers that we test horses. It insures that we do not put their pasture mates at risk.

Recently we have learned more about the transmission of this disease. The disease is spread by horseflies. The large horsefly is the main vector. If they bite an infected horse and then bite a healthy horse, the disease gets transmitted. The virus does not live for very long on the horsefly, maybe as little as fifteen or thirty minutes. So for one horse to infect another they must be close to each other. This disease occurs anywhere horseflies live.

Three different sets of symptoms occur: acute, chronic and the asymptomatic carrier. With acute infection the horse has fever, depression, and no appetite. The acute horse may be difficult to diagnose because the symptoms are very general and he will not be positive on the EIA test for a month and a half. Approximately one third of infected horses will die of the acute form within a month.

The chronically infected horse will having recurring acute bouts along with weight loss, ventral edema (swollen belly and legs) and anemia. These horses will be positive on a EIA test. These horses may linger for a year or more before they die.

Most asymptomatic EIA infected horses will not show any recognizable signs but will test positive on a Coggins test.

To insure that an animal is not harboring the virus a simple test is performed, the Coggins test. The Coggins test checks for Equine Infectious Anemia (EIA) antibodies in the horse's blood. Blood samples must be sent to a state approved laboratory. This test is often needed to take your horse to a show and whenever you transport your horse across state lines. It is to prove to others your horse is safe to be around their horses. Some states now require a negative Coggins test on a horse before he can be sold. Before you travel check to see how recent a test is required because it differs from place to place.

Once you have a negative Coggins further testing is not required for your own peace of mind. Your horse will not become EIA positive unless he develops a serious, febrile illness after contact with a horse of unknown EIA status. You may be required to have a test done yearly to show or transport your horse, so other people will know your horse is safe.

The current testing program has gone a long way toward reducing this disease. Few people remember, prior to the testing in the 1970's that this disease killed many thousands of horses annually. It was originally thought that the testing program would eradicate EIA but every year there are just enough asymptomatic carriers to perpetuate the problem.

There is no vaccine for EIA. It is important that you be careful that your horse's pasture mates are as healthy appearing as your own horse. Board your horse only where a negative Coggins test is required of all horses before they come on the premises. This is your best protection.

See EQUINE INFECTIOUS ANEMIA in the Disease Section.

Other Resources:
Equine Infectious Anemia Statutes and Regulations
Statutes and regulations dealing with equine infectious anemia (swamp fever), including those requiring Coggins Tests before the showing, sale or transportation of a horse.


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