The recent news of an equine infectious anemia (EIA) outbreak among a string of Quarter Horse racehorses in California, New Mexico, and Texas has highlighted the importance of using sterilized medical equipment and biosecure injection techniques when treating horses, as well as the need for routine EIA testing.
EIA is a potentially fatal blood-borne infectious viral disease that produces a persistent infection among equids. Transmission often occurs via certain species of biting flies, which transfer the virus in blood from infected horses.
EIA Transmission in Horses
EIA can also be transmitted iatrogenically via medical equipment such as needles, syringes, IV tubing, or other equipment contaminated with blood or through transfusion of blood or blood products from an infected horse. Transmission from the mare to foal in utero has also been documented, and the EIA virus has been isolated from semen of infected stallions. Infection does not occur with horse-to-horse contact unless there is an exchange of blood.
The United States Department of Agriculture’s Animal and Plant Health Inspection Services determined the Quarter Horses in the care of one trainer had contracted the virus through iatrogenic transmission.
Previously, natural transmission by biting flies in untested or under-tested horses was the main cause of cases in the U.S. In recent years, however, the epidemiology of transmission has shifted. Now, most EIA cases reported each year result from iatrogenic transmission, particularly in Quarter Horse racehorses. Many of these cases have ties to unsanctioned racing and the reuse of blood-contaminated equipment. Some cases have involved horses illegally moved from Mexico, where the disease is widespread and endemic. Infected horses from these high-risk populations are often in close proximity with other horses during transport, where they can serve as a source of continued transmission.
The incubation period for horses infected with EIA is usually 15-45 days. Infected horses are lifelong carriers. Horses showing clinical signs of the disease are more of a threat to healthy populations because of higher levels of virus circulating in the blood.
EIA Prognosis
Horses that survive the initial clinical phase of the disease usually become outwardly inapparent carriers and remain a reservoir for the disease for the rest of their lives. There is no treatment or cure for EIA. Horses are usually euthanized if confirmed positive for the disease to prevent ongoing transmission to other horses. If not euthanized, horses must be permanently quarantined at least 200 yards away from non-infected horses to prevent spread of the disease by biting flies. Infected horses cannot be moved from quarantined premises except by approval of state and federal animal health officials.
Clinical Signs of EIA in Horses
Clinical signs of EIA include fever, depression, low platelet count, anemia, red or purple spots on the mucous membranes, edema, muscle weakness, and atrophy, although chronically infected horses often show no obvious clinical signs of disease.
Diagnosing EIA
EIA is diagnosed by testing antibody levels in the blood. The most common test used is the Coggins Test, which is an agar gel immunodiffusion (AGID) test. The ELISA (enzyme-linked immunosorbent assay) test is also available to detect EIA antibodies. Veterinarians must collect and submit blood to certified laboratories for testing.
EIA Prevention Strategies
There is no vaccine available for EIA. Methods of prevention include vector control to reduce the possibility of transmission by biting flies and ensuring needles, syringes, and intravenous administration sets are not reused unless sterilized. Any other medical equipment that can be contaminated with blood, such as dental equipment or stomach tubes, should never be shared between potentially affected horses. Sterile technique must be used when administering intravenous drugs to avoid introducing contaminated blood into a multidose vial of equine drugs. Blood transfusion between horses should only be conducted by veterinarians using EIA-negative blood donor horses.
Veterinarians should perform routine EIA testing in their clients’ horses to ensure horses have not contracted the virus; this prevents transmission to other horses. Many equine events and boarding facilities require proof of a negative Coggins Test within the previous 12 months to enter the facility. States require a negative EIA test for interstate movement, and some states require an EIA test for change of ownership.
The EDCC reports all cases submitted by state animal health officials in the United States and Canada.
Related Reading
- Equine Infectious Anemia Virus (EIAV)
- The Future of Equine Infectious Diseases in a Changing Climate
- Horse Owner Knowledge and Use of Biosecurity
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