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We see this all the time and most of us know that most states require that horses entering or being transported across their lines have a negative Coggins Test no more than six months old. This effects everything we do with our horses - travel for horse shows, trail rides, clinics, boarding facilities and all other doings we like to take our horses to. But, why?

EIA (Equine Infectious Anemia) is sometimes called "SWAMP FEVER" because of the higher incidence on the Gulf Coast of the United States, where increased humidity and temperature are favorable for transmission of the disease. It is diagnosed by a blood test called the Coggins test, named for its developer, Dr. Leroy Coggins, the veterinarian who developed the test in 1970. It is an agar-gel immunodiffusion (AGID) test and is capable of detecting inapparent virus carriers. This disease is caused by a virus that infects red blood cells of horses, mules, donkeys, and zebras. The infected animal's body responds to the virus by mounting an immune response to the infected red blood cells, destroying them and causing the horse to become anemic (low red blood cell count). Additionally, studies to develop an effective vaccine have been disappointing. Once infected, horses remain infected for life. Although this disease has affected horses for a long time, researchers have recently grown more interested because the EIA virus is closely related to the human immunodeficiency virus (HIV).

EIA is transmitted primarily by bloodsucking insects. The horsefly is the most common. The large size and painful bites of these flies make it unlikely that a horse would permit them to complete a blood meal uninterrupted; by tail swishing or twitching, they send the biting fly on its way. This is the problem, however, because the virus is transmitted to other horses when the horsefly starts his meal on an infected horse and completes it on an uninfected one. Infected mares can transmit the disease to their foals and blood contaminated needles, syringes, etc. can also act as carriers.

An anemic horse is depressed, lethargic, loses weight, and easily gets sick from other diseases. About one-third to one-half of infected animals, develop clinical symptoms and suffer from fever, dramatic weight loss, or swelling around the chest and legs. Some die. Others will demonstrate no symptoms and are referred to as "inapparent carriers". Although horses in the chronic stage appear normal, they become ill again if subjected to stress, such as shipping or severe weather. Carriers pose a health threat to the equine community.

Testing a horse for EIA involves drawing blood, filling out the proper paper work, and submitting the sample to a laboratory for testing. There are local laboratories that can provide test results in 24 - 48 hours. A negative result indicates that the horse is not infected. A positive Coggins Test means that the horse is infected with the EIA virus.

If a horse tests positive, strict quarantine measures are imposed. These include confinement in a screened stall and a 200-yard buffer from all other horses. Often, owners elect to euthanize their horses rather than subjecting them to such strict isolation.

Even if you don't show your horse, it should have an annual Coggins Test. Horses that are shown or transported regularly may require more frequent testing. This test, along with improved knowledge about EIA transmission, has made effective control of the infection among horse populations a reality.

Because of the relatively low incidence of EIA in the United States, most horse owners and veterinarians have decided that additional regulations are not necessary. Last year, 76,000 horses were tested in Kentucky, with 20 horses testing Coggins-positive. In Virginia, 40,000 were tested, with eight positives. Nevertheless, if you plan to buy a horse or board a horse, require either a recent negative Coggins from the owner, or isolate the horse until the test is performed.

For further information contact your veterinarian.