Coggins Test for Equine Infectious Anemia (Swamp Fever)

Q:My horse was turned away from a horse show because we didn't have proof of a current negative Coggins test. Is it really that important?


A:To answer the question directly, you were turned away because it is customary to monitor the serum of horses for antibodies to equine infectious anemia virus (EIAV)--and we use testing to prevent the movement of virus carriers and spread of the infection caused by that lentivirus (a virus that can cause slowly progressive, often fatal animal diseases). 

The Coggins test is the most commonly used means of finding antibody to EIAV, which causes a persistent infection in horses that's often termed "swamp fever." There also are four rapid ELISA tests for EIA. ELISA test results can be obtained within an hour. A Coggins test result requires at least 24 hours. Testing for EIA has been done for years to identify virus carriers and to regulate their movement. There are no treatments or vaccines for this lentivirus, which is a relative of HIV in humans. For more information on EIA, see other equine infectious anemia articles on TheHorse.com

Since there is no cure for the infection, currently we can only control its spread by permanently quarantining test-positive horses or euthanizing them.

The potential for spreading EIA is highest at congregation points when horses are in close contact. Although transmission in nature is generally effected by transfer of blood between horses through the interrupted feeding of insects, e.g., horse flies, man has repeatedly proven to be thousands of times more effective than insects (i.e., by sharing needles between infected and non-infected horses). To stop the spread of the infection and disease, one must know the status of each individual and control movement of test-positive animals. The highest-risk scenario is a congregation point (such as a horse show, trail ride, or other competition) that does not require a negative test for EIA.

Actually, a negative test result for EIA is only accurate the day the blood is taken. If our horse is test-negative and all its contacts have been, are, and will be test-negative (as are all their contacts), we can rest assured that our horse will remain test-negative. Therein lies the rub: Testing of 100% of our contacts is virtually impossible.

The greatest risk of acquiring EIA today in the United States is from the "untested reservoir" population. While two states require annual testing, no one has yet been successful in testing 100% of the horses in their jurisdiction. To test every equid would allow us to eradicate EIA from the population. Each state has its own set of regulations to monitor EIA. In some areas, testing has been done on a regular basis over a long period of time, with very few positive cases found in recent years. Evidence of a negative test for EIA is required to move a horse on a public road in the state of New York--regulations such as these have thwarted the spread of the infection and disease.

I recommend that all horses considered for purchase have evidence of a recent negative test for EIA. If there are questions about the status of all the previous contacts of the horse, we recommend the sale be contingent on a second negative test at least 45 days, preferably 90 days, after the transfer to have more confidence.

About the Author

Charles Issel, DVM, PhD

Charles J. Issel, DVM, PhD, is the Wright Markey Chair of Equine Infectious Diseases at the Gluck Equine Research Center at the University of Kentucky. He has studied equine infectious anemia since 1974 while on the faculty at Louisiana State University (until 1990) and at UK. Issel bred Thoroughbreds in Louisiana prior to working at UK.

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