The History of Equine Infectious Anemia
By Debbie Clark MPH, William Jeter DVM

Equine infectious anemia (EIA), commonly known as swamp fever, is a viral disease that attacks the horse's immune system. There is no cure for this disease, which is caused by a retrovirus closely related to the Human Immune Virus (HIV) in humans. It has a death rate of up to 30% in acutely infected animals. A surviving infected animal will remain a carrier of the disease, and, therefore pose some degree of threat to other horses for the rest of its life. Currently there is no vaccine to prevent a horse from contracting the disease.

EIA has been around for a long time, at least 160 years, and research to understand it has been in progress for nearly as long. The first case of EIA recorded was in France in 1843. Scientists who noted the symptoms thought perhaps it was a nutritional disease. If they tried to "cure" the horse by adjusting the feedings, they soon found out it didn't help the depression, fever, weakness and weight loss the horse was experiencing. By the time the disease was recorded again in 1861, they had begun to wonder if a nutritional problem was really the cause.

Two years after the second outbreak in France, EIA was documented in Switzerland; then, two years after that, in Germany, where it spread through the German cavalry horses. Since then, nearly every European country has reported cases of EIA, as have Russia, several African countries and much of Asia. Japan had one of the first epidemics. During the first decade of this century more than 300 horses a year died from "Swamp Fever" in the pastures of that small country.

In 1888 the first case was reported in North America. It was discovered in Wisconsin and was known as "Equine Relapsing Fever". By the 1890s it had appeared in Wyoming where the first extensive U.S. epidemic on record raged in 1901. By 1909, EIA had been reported from ten states: Nevada, Minnesota, Wisconsin, Wyoming, Montana, North Dakota, Kansas, Colorado and Texas. For a while after that the number of cases decreased. Then, in 1935, EIA was reported in New England. There was no question the virus was still spreading. At that time it existed in 17 states. Six years later a researcher reported that EIA was even more widespread than reports indicated. He had authentic accounts of it from 29 states of which 15 had been scientifically confirmed by horse-inoculation tests. In a horse-inoculation test, examiners draw blood from a horse suspected of having EIA and inject it into a healthy horse. If the healthy horse shows symptoms of EIA after a reasonable incubation period, then they know the suspect has the disease. This was the only method of diagnosis at that time.

In 1947 New Hampshire witnessed an outbreak that was considered a major epidemic. Seventy- seven Thoroughbred horses died or were euthanized at Rockingham Park Race Track. The start of the epidemic was traced to a race horse brought from Florida. By now the disease was reported sporadically from 34 of the 48 states.

During the 1960s, EIA was recognized as a major problem in horses on Standardbred farms in New York State. In 1970, personnel in the Equine Infectious Disease Laboratory at Cornell University investigated 10 outbreaks, the most serious of which involved 46 horses on a farm of about 425 horses. This outbreak has been reported in detail in veterinary literature. All of these outbreaks were explosive in nature and in most cases one or more horses had died from the infection before the disease was recognized.

In 1965 the United States Livestock Sanitary Association (now known as the U.S. Animal Health Association) along with other national veterinary and horse industry groups, developed positive uniform plans for quelling the disease. This move was brought about in response to widespread epidemics occurring at other racetracks in Maryland, Florida, Washington and Illinois. Their principles, known as the "Prospectus on Equine Infectious Anemia with Guidelines" was instrumental in halting the spread of EIA by the latter part of 1966.

Then, in 1970, Dr. Leroy Coggins of Cornell University developed the first accurate laboratory procedure for diagnosing the disease. Now a household term among U.S. horsemen, the "Coggins Test" is a laboratory procedure designed to detect the presence of antibodies, or virus-fighting units in the blood stream of an animal being tested. The Coggins Test does not detect the EIA virus itself, but the scientific community is agreed that the presence of antibodies to fight disease is ample proof that the virus has infected the animal. In 1973 the United States Department of Agriculture designated the Coggins Test the official test for determining the presence of EIA; established a procedure for certifying a network of laboratories qualified to run the tests; and prohibited interstate transport of EIA positive "reactors" except for purposes of taking them to an approved slaughterhouse, quarantine site or research facility.

In October 1973, Florida implemented one of the first rules in the nation, and that rule made the Coggins Test the offical test for detection of the EIA virus in horses at the state level. The Coggins Test then became mandatory in the state of Florida for horses being sold, raced, and in most cases, shown or bred. A quarantine directive was imposed upon horses found to be positive. The directive states that "an infected animal has to be kept isolated in approved quarters until death or destroyed". Many horse owners whose horses tested positive but did not show outward signs of disease (inapparent carriers) felt that these control measures were too stringent and supported adoption of a more moderate regulatory approach.

In one such case brought to trial on August 11, 1976 in Broward County, Florida, a member of "United We Ride" contended that the Florida regulations deprived them of due process of law and requested relief from the quarantine that resulted when their horses tested positive. Broward County Circuit Judge, Thomas B. Reddick, concluded that the plaintiffs were "entitled to some relief"; that the Coggins Test alone should not determine disease status; and the final decision would be made by the individual's veterinarian. However, upon appeal of the Circuit Court's decision, the Appellate Court overturned the ruling, finding in favor of the State of Florida on all counts.

In spite of the state being located in the EIA "hot zone" (Gulf coast states), Florida's EIA Disease Control Program continues to keep the disease incidence at a very low rate. For example, when 1,576 horses were tested in Florida between December 1, 1970 and July 30, 1971, 190 tested positive, or 12%. When 120,402 horses were tested in Florida between July 1, 1999 and June 30, 2000, 20 tested positive, or (0.016%). This downward trend is a direct result of the effective disease control activities, strict enforcement of EIA regulations and strong support of the state's valuable equine industry. Until a vaccine becomes available in this country, control programs are the only viable option to reduce the risk of transmission from virus-infected equines. Future methods to increase the effectiveness of control programs include: (1) Increasing the number of quarantine farms in areas where large numbers of equines are affected, (2) Increasing revenue generated and allocated to EIA research, and (3) Educating the horse owner of the biological risks of EIA and therefore placing less emphasis on the perceived or psychological threats of the infection.

Bibliography Dr. C.L. Campbell, History of Equine Infectious Anemia and Remarks to the Current Status of the Disease as Viewed by a Regulatory Veterinarian. December 11, 1976.

C.J. Issel, DVM et al., Equine Infectious Anemia. The Horse Interactive. August 1999.

Equine Infectious Anemia Brochure. A Publication of the Division of Animal Industry, State of Florida, FS 585.671.

Florida Horseman Newspaper. Volume 6, Number 4. July, 1977.

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