What is a Coggins test and why should I have one done on my horse?

These include

* Test all horses for EIA at least annually. Horses that travel in or come from, areas where the incidence of EIA is higher should be tested more frequently. The Gulf Coast states have the greatest number of positive tests each year because the temperature and humidity favor a prolonged vector season

* Stable owners should require a current negative coggins test before introducing new horses

* Horse show and event managers should require and verify all certificates. Enforcement of these rules is important

* Needles or syringes should never be used on multiple horses

The coggins test is a blood test used to diagnose the disease Equine Infectious Anemia (EIA) sometimes called swamp fever. EIA is a viral disease of horses and other Equidae such as ponies, mules, and donkeys. Once infected, the animal is infected for life. There is no effective vaccine and no known cure. When infected with the virus, the horse will develop a fever, be off feed, and possibly show some bruising of the mucous membranes. After recovering from the initial illness, some horses develop recurring cycles of the above symptoms, that lead to the classic signs of anemia, weight loss, and ventral edema. The frequency and severity of these episodes decrease with time. Most horses do not die, but become asymptomatic carriers (i.e., animals with no signs of illness who are still capable of spreading the disease). Many horses that are infected will show very few of these symptoms and quickly become asymptomatic carriers. These mild symptoms can easily be mistaken for other less serious diseases. Animals that are currently showing signs of disease have larger amounts of virus in their blood than asymptomatic carriers, but both can spread the disease. EIA is not contagious to people and is not directly contagious from horse to horse. It can only be spread via contaminated blood. The most likely way this occurs is via blood-sucking insects such as horseflies, deer flies, and less frequently mosquitoes. Insects are mechanical vectors that carry the virus from horse to horse without becoming infected themselves. Since the virus only survives on their mouth parts for between thirty minutes and four hours, the insect must be interrupted while feeding on one horse and finish its blood meal on another to spread the disease. Characteristically the interrupted insect will try to finish its blood meal as quickly as possible. This may mean biting the same horse again, or biting a nearby herd mate. Research has shown that if the horses are separated by more then 200 yards the chances are much greater that the insect will bite the same horse again rather then travel the 200 yards necessary to bite another horse. This fact is the basis of currently used quarantine methods and will be discussed later in this article. Horseflies and deer flies are more likely to be involved with the spread of EIA than mosquitoes for two reasons. First, their mouth parts hold more potentially infected blood. Secondly, their bites are more painful which makes it more likely that the horse will do something to interrupt their feeding. The virus can also be spread by blood contaminated needles or surgical instruments. The first case of EIA was recorded in France in 1843. North America reported its first case in 1888 in Wisconsin, where it was known as “Equine Relapsing Fever”. In 1901 Wyoming was the site of the first extensive epidemic in the U.S. An epidemic in 1947 at Rockingham Park Racetrack in New Hampshire resulted in seventy-seven horses either dying or needing to be euthanized. Dr. Leroy Coggins of Cornell University developed the first accurate laboratory procedure for diagnosing EIA in 1970. The test does not detect the virus itself, but it does detect the presence of antibodies in the blood. Scientists all agree that the presence of antibodies is proof of infection by the virus. The U.S. Department of Agriculture made the coggins test the official test for EIA in 1973. The Federal government does not require a coggins test prior to the interstate shipment of horses, but it does require one before a horse can be imported. Most laws dealing with EIA are established at the state level. Most states generally require at least a health certificate and a negative coggins test for a horse to enter the state. A few states require coggins testing within the last six months, but most will accept results from the last twelve months. Pennsylvania only requires a coggins test to enter the state. There are no coggins test requirements for intrastate movement or entrance into individual shows or sales, that decision is left up to the organizers of the event. Other states have more stringent laws. Some require a coggins test before a change of ownership, and a few states require any horse transported on a public highway to have a negative test. Since most horses that test positive are asymptomatic carriers, the state of Michigan last year took a further step to control EIA. Not only are they continuing to require horses entering the state to have a negative coggins test, but they are also requiring a onetime mandatory testing of all resident Equidae. This would identify any long-time resident asymptomatic carriers in the state that are not shown or taken to other events that require a coggins test, but that could serve as a reservoir to spread the disease. States are also debating the virtues of a coggins test being good for only a calendar year as opposed to a year from the last test. This method uses the winter months, when there are no vectors to spread the disease, to allow the horse that was infected during the previous summer to develop antibodies. These antibodies would then be detected by a coggins test before the horse was exposed to other horses during the next vector season. For example, a horse that was tested negative on July 1, 2002, but that was infected on July 10, 2002, would be considered negative until June 30, 2003, and eligible to go to horseshows and possibly spread EIA to other horses until then. In a state that goes by calendar year, that same horse would not be eligible to be shown in 2003 until it was tested. Protecting a horse from exposure is the only way to prevent EIA. The coggins test is a valuable tool in reducing the number of horses serving as a reservoir for insects to spread the disease. A federally accredited veterinarian fills out a form that positively identifies the horse. Blood is then drawn and sent to an accredited laboratory. If the test is negative, the owner receives a certificate stating this. If the test is positive, the state authorities are notified and the farm is quarantined and the horse is separated from the other horses and retested. If the second test confirms that the horse is infected, then all “exposed” horses are tested. States define “exposed” differently. Some states consider any horse within three miles exposed, while other states consider 200 yards or less exposed. The exposed horses are tested every thirty to sixty days until no new positive tests are found. The reason for this is after exposure it can take up to forty-five days for a horse to develop antibodies and subsequently have a positive coggins test. The horse that tested positive can be dealt with in three ways. First is euthanasia. Second is shipment to a recognized research facility or slaughterhouse. Third, the horse can be permanently identified with a tattoo or brand, and quarantined at least 200 yards from any other Equidae for life. These methods of dealing with positive horses have not eradicated the disease, but have significantly decreased the incidence. In 1972, 12.8 percent of the 12,086 horse tested in the Gulf Coast states were positive and 2.6 percent of the 66,675 horses tested in other states were positive. By 1975, the incidence of positive horses in the Gulf Coast states had dropped to 4.4 percent and to 1.06 percent in the other states. In 1988, the U.S. reported 3,513 of 853,786 or .42 percent of all coggins tests performed were positive. Several things can be done to help protect horses from exposure. These include

* Test all horses for EIA at least annually. Horses that travel in or come from, areas where the incidence of EIA is higher should be tested more frequently. The Gulf Coast states have the greatest number of positive tests each year because the temperature and humidity favor a prolonged vector season

* Stable owners should require a current negative coggins test before introducing new horses

* Horse show and event managers should require and verify all certificates. Enforcement of these rules is important

* Needles or syringes should never be used on multiple horses

Equine Infectious Anemia: The clinical signs, transmission, and diagnostic procedures. Veterinary Medicine, September 1990.pg. 1007-1028. Morris.D.D.,Warner, A.Hemolytic Anemias.in Current Therapy in Equine Medicine Vol. 2, pg. 297-299. Clark,D., Jeter,W. The History Of Equine Infectious Anemia. http://www.florida horse.com /EIA.html accessed 1/16/02 Equine Protection Network, Equine Infectious Anemia Outbreak in PA.,http://members.tripod.com/~EPN/press/preia.htm accessed 1/19/02. Dawson,R., Your Horse, Equine Infectious Anemia, and the Law. http://www.law.utexas.edu/dawson/horselaw/eia.htm accessed 1/16/02. Pennsylvania Equine Infectious Anemia Statutes and Rules, http://www.law.utexas.edu/dawson/eia/pa_eia.htm accessed 1/16/02. Michigan Department of Agriculture News Release, Michigan equine testing rules changed, http://www.mda.state.mi.us,accessed,1/16/02.

Prepared by Dr. Ed Jedrzejewski, Assistant Manager, Penn State Equine Unit