If horses survive the first two stages, they enter the final or chronic stage, where they often appear normal. An owner may report that a horse is a poor keeper, and the animal may be mildly anemic. Infected mares can transmit the disease to their foals. A horse infected with the EIA virus will be a carrier of the disease for life. Although horses in the chronic stage appear normal, they become ill again if subjected to stress, such as shipping or severe weather.
Carriers pose a health threat to the equine community.
Since the early 1960's, several outbreaks of EIA have occurred at either race tracks or large breeding farms, resulting in the deaths of many horses. The Coggins test, developed in the 1960's by Dr. Leroy Coggins, is based on the detection of antibodies in the horse's blood. Once a horse is infected with EIA the antibodies will be present in the blood for life. Even if you don't show your horse, it should have an annual Coggins test. Horses that are shown or transported regularly may require more frequent testing.