By Charles J. Issel, DVM, PhD
Purchasing A Horse - Jun 18th, 02
My horse was turned away from a horse show because we didn't have a current negative Coggins test. Is it really that important?
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. There also are three 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 more than 25 years to identify virus carriers and to regulate their movement. There are no treatments or vaccines for this lentivirus relative of HIV in humans. Since there is no cure for the infection, currently the only options for control of the spread of the infection are permanent quarantine of test-positive horses, or euthanasia.
The potential for spreading EIA is highest at congregation points like horse shows, when horses are in close contact. Transmission is generally effected by transfer of blood between horses through the interrupted feeding of insects, e.g., horse flies. 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.
In Utah, infections with EIA have been found in feral, free-roaming horses. Routine testing for EIA of domesticated horses at risk has not occurred in that area historically. When domestic and wild horses intermingle, there is risk of EIA infection either being introduced by the domesticated horses into the wild population, or the other way around. Most likely both circumstances could occur.
The greatest risk of acquiring EIA today in the United States is from the "untested reservoir" population. While some states have annual testing, no one has 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. This is the case in the northeast, for example, from Maine to Maryland, where an average of two horses out of nearly 200,000 tested each year has been positive. 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 about 45 days after the transfer.
One idea to help increase testing for and awareness of EIA is for the states to grant a "reward" to owners who remove test-positives from their herds.
Charles J. Issel, DVM, PhD, is the Wright-Markey Professor of Equine Infectious Diseases at the Gluck Equine Research Center, University of Kentucky