November 2006
From the State Vet's Office

Equine Infectious Anemia and Coggins Tests

by Dr. Tony Frazier

The horse industry is BIG BUSINESS in Alabama.  Consider that there are over 100,000 horses in the state, according to the Alabama Horse Council, and horses account for 20 per cent of the economic impact that agriculture has on the State of Alabama.

Swamp fever is what they used to call it.  That’s because Equine Infectious Anemia used to be so prevalent in the coastal areas of the Southeast.  The disease was first diagnosed in France in 1843.  Several years later in 1888, it was diagnosed in North America where it was called Equine Relapsing Fever.  The first extensive epidemic is reported to have occurred in Wyoming in 1901.

The virus that causes Equine Infectious Anemia (EIA) is a retro virus from the lentivirus family, the same virus family as the human AIDS virus.  There is no known threat to humans by the EIA virus.  The lentivirus family has the characteristic of possibly having a very long incubation period—that is the length of time between exposure and infection until the host begins to show signs of illness.  That means the virus could be present in an equine host for a long period of time, yet the animal will appear completely healthy.  While disease can develop within a few weeks of being infected, it most often takes months to years.

The virus is most often transmitted by horse flies that feed on the blood of an infected horse, and then feed on one that is not infected.  It can also be spread by brushes, combs, tack, bits, and using hypodermic needles on more than one horse.

Once infected, the horse will remain infected for life.  The disease itself is manifest in three forms:  acute, subacute, and chronic which may become fatal.

In the acute disease, the horses, ponies, mules, or other equids become very ill.  They will have a high fever, possibly swelling in the legs and lower abdomen, be lethargic, and simply appear to be very sick.

In the subacute form of the disease, the animal will not be as ill as the acute animal, but will be somewhat sick.

The chronic phase occurs if the horse survives the acute or subacute phase of the disease. The chronic animal will have recurring episodes of illness and may recover, only to have a later episode.  These animals often are on a roller-coaster ride that will eventually lead to their demise.  There is no effective vaccine and no cure.

For years, the diagnosis of the disease was complicated and had some room for error.  In 1970, Dr. Leroy Coggins developed a diagnostic test that could detect not the presence of the virus, but antibodies to it that an infected horse had produced.  The test is what we call the Coggins Test.  While it may take up to sixty days for an infected horse to become positive, it is a very good diagnostic test.  In 1973, the USDA made the Coggins Test the official test for EIA.

In the State of Alabama, our Veterinary Diagnostic Laboratory runs about 20,000 Coggins Tests annually.   Besides those there are private laboratory companies that will run many more tests on Alabama horses.  If any private laboratory or our lab gets a positive, the horse and its herd of origin are retested by animal health officials at our laboratory, then sent to the National Veterinary Services Laboratory in Ames, Iowa.  Dr. Sara Rowe, who is in charge of EIA testing at our laboratory, is extremely conscientious about the tests.  The retest on positives is run in ways to make sure it is not a false positive.  During the past year, there were 9 positive EIA horses.

Once the horse is officially declared to be positive, it must be branded with a cold brand or hot brand with “64A” on the left side of the neck.  Then there are three possible dispositions of the horse.  First it may be euthanized or permitted to slaughter on a restricted movement permit. The second possibility is to house the horse in an approved screened stall that will be periodically inspected to make sure flies are not a transmission factor (nearly impossible).  Finally, the horse may be isolated at least 150 yards from any other horse for the rest of its life (also periodically checked to assure compliance).

To protect your own horses and the equine industry in Alabama, we recommend that you have your horse tested annually for EIA.  If you have questions about the test, please discuss them with your local veterinarian.  If you have questions about EIA regulations, call us.  My number is 334-240-7253.