The Coggins Test in Horses – Equine Infectious Anemia

The Coggins Test - Coggins - Coggins Test

Equine Infectious Anemia – The Coggins Test
American Association of Equine Practitioners
By: Robert N. Olgesby, 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.


The only way to accurately determine whether a horse is infected with the EIA virus is by identifying antibodies in the blood via agar gel immunodiffusion (AGID) or competitive enzyme linked immunoadsorbent assay (C-ELISA) tests. The AGID method is considered the “gold standard” and is commonly known as the Coggins test. This test was developed 25 years ago by veterinary researcher Dr. Leroy Coggins. A negative Coggins test means there are no detectable antibodies at the time of testing. A positive test indicates the horse is infected and a carrier of the virus. C-ELISA tests offer the advantage of rapid results. However, false-positive results are more common with the C-ELISA tests and positive results should be verified by a standard Coggins (AGID) test. Foals may be false positive due to maternal antibodies passed via colostrum for as long as six months with either test. 

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.


There is no effective treatment for EIA. There is no vaccine to prevent it. There is no cure. However, good management can reduce the potential of infection. The following guidelines will help:

  • Use disposable needles and syringes (one per horse) when administering vaccines and medications.
  • Sterilize dental tools and other instruments before using them on another horse.
  • Test all horses for EIA at least annually.
  • Test horses at the time of purchase examination.
  • Stable owners, horse show and event managers should require and verify current negative Coggins certificates for all horses entering the premises.
  • New horses should be quarantined for 45 days and observed for any signs of illness, including elevated temperatures, before introducing them to the herd. They should be retested if exposure to EIA is suspected at a 45-day interval.
  • All stable areas should be kept clean, dry and waste-free. Good pasture management techniques should also be practiced. Remove manure and provide adequate drainage to discourage breeding sites for pests.
  • Horses that are at greater risk (such as animals who are in frequent contact with outside horses or who live or travel in geographic regions known for EIA outbreaks) should be tested more frequently, ideally every four to six months.

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.

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.

Equine Infectious Anemia – The Coggins Test
Information Form

The Coggins Test - Coggins - Coggins Test

Contact us by phone (800) 874-9191, FAX (602) 992-8327
or email below for more Equine Infectious Anemia – The Coggins Test information.

The Coggins Test - Coggins - Coggins Test