Standardbred racehorse owners got a scare last week when officials quarantined three barns of horses at the Red Mile, a harness track in Lexington, Ky, because of serologic test results that suggested a horse might have had equine infectious anemia (EIA). That quarantine was brief, however, as further tests indicated that the horse was not suffering from an active infection.

Equine infectious anemia is also referred to as swamp fever, mountain fever, slow fever, and malarial fever. It is a very serious blood disease of equids. The virus is transmitted by biting insects, so a carrier horse can be a reservoir of the disease that endangers other horses of being infected.

An owner of a horse with confirmed EIA must quarantine the horse under highly restrictive conditions, possibly for life, or have him euthanatized.

Rusty Ford, Equine Programs Manager at the Kentucky Department of Agriculture, summarized, "There was an animal that falsely tested positive to one of the many tests for EIA, and since that time, we have done extensive diagnostics and have determined the animal to not be infected."

Kentucky state veterinarian Robert Stout, DVM, explained the specifics of the situation in a letter to local veterinarians: "The index horse--a 3-year-old Standardbred colt--was shipped from a training facility in Illinois to the Red Mile harness track in Lexington the previous week with a negative AGID (agar gel immunodiffusion test) dated April 2004. He is currently is in training and in excellent physical condition and not demonstrating any clinical signs suggestive of infection."

The test in question (an enzyme-linked immunoassay test, or ELISA test) was done in preparation for shipment to Canada.
Stout continued, "During this past week, my office--with assistance from the University of Kentucky Livestock Disease Diagnostic Center, Gluck Equine Research Center, and USDA--has investigated an ELISA positive result for equine infectious anemia.

"Upon notification of the positive reaction (Friday, Oct. 8), the index horse was removed from the track and quarantined per KDA regulations," he continued. "A risk assessment of the situation resulted in the quarantine of 37 additional animals in three barns, which were segregated from the main stabling area. Subsequent testing of these horses was negative."

The original serum sample of the index horse and another sample were submitted for supplemental testing, including the Western Blot test, at Gluck's reference laboratory. Stout reported, "These results were reported positive to the original ELISA kit, negative to the other two kits, and negative to the Western Blot test. Slight reactivity was noted in AGID tests from two different manufacturers."

The 37 animals determined as having possible exposure to this animal were tested from samples collected on Oct. 13. All were reported negative and released from quarantine.

Stout concluded, "After reviewing the history, results of the diagnostic testing, and in consultation with research and epidemiologic specialists, it was concluded that the index horse is not infected with EIA, and there is no evidence to suggest recent exposure. Explanation for the positive ELISA reaction and the inconsistent reactivity noted in the AGID tests will be pursued. The index horse is deemed negative for EIA, and the quarantine has been released."

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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