EIA Reservoir Implications

Charles Issel, DVM, PhD, spoke about the implications of reservoirs of Equine Infectious Anemia (EIA) at a seminar hosted by the University of Kentucky's Gluck Equine Research Center in Lexington, Ky. Issel began by stating that most EIA affected horses are inapparent carriers. These horses are only found to be positive when they are routinely tested for the disease. In the United States 1.3 million horses are tested for EIA every year with the most common method of testing being the Coggins test.

Issel said the trend for new positive cases is that they are not coming from the “hot zone,” but rather areas where EIA has not historically been a problem. Issel added that the reason for this trend is that over 90% of horses being tested for EIA are located in the “hot zone,” and states included in this area have addressed the problem of EIA. The areas that are historically known for EIA have programs in place that minimize the risks of transmission.

To detect reservoirs of EIA a practical program needs to be implemented along with area wide education programs addressing this disease. Issel suggested issuing health certificates for negative horses and placing positive horses under quarantine. Further, and perhaps the most important aspect of making sure a program of this sort works, is gaining the involvement of the equine industry, veterinarians, and industry leaders. The goal is to have people test their horses for EIA after educating and informing owners about this disease, Issel said.

This past summer an EIA reservoir was found in Utah in wild horses. The index cases came from the Ute Nation which owns land adjacent to land owned by the Bureau of Land Management. While some EIA positive horses were found on BLM land, the majority of positive cases were from land owned by the Ute Nation. To deal with the problem, the Ute Nation slaughtered all horses that tested EIA positive. In the cases of positive horses on BLM land the solution was not so easy. Here, there were federal regulations to follow. The adult horses that tested positive were slaughtered while the foals that tested positive were isolated and retested at a later date. The retesting was performed because it's possible that foals were only testing positive due to the maternal antibodies they were receiving from their EIA positive dams. These foals were retested at a later date and only one of those foals continued to test positive.

What was learned from this experience in the wild horses, Issel said, is that EIA was probably present in this area for 20 years but it had not spread too far. Adding that stallions were infected at a higher rate than the mares and older horses (4 years and older) tested positive much more frequently than younger horses. This can be attributed to the fact that the older a horse the longer time it has had to come into contact with the disease, noted Issel.

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