By C.J. Issel, DVM, PhD, Wright-Markey Chair of Equine Infectious Diseases, University of Kentucky


These days the main thing many U.S. horse owners think about the Coggins test is that it’s something they have to have done before taking horses to a show, sale, or another state. Its often overlooked purpose of identifying horses carrying equine infectious anemia (EIA, often called swamp fever) is critical to controlling the disease. Yet EIA researchers are now recommending that we test many horses less frequently and focus more effort on finding untested carriers.

Equine infectious anemia is an often fatal blood-borne disease of horses, donkeys, and mules caused by a lentivirus that’s closely related to the human immunodeficiency virus (HIV). Although some infected horses won’t become ill, others will display fever, anemia (low red blood cell count), jaundice, depression, edema (fluid swelling), and chronic weight loss. The virus is transmitted by blood-feeding insects and sharing of blood-contaminated equipment such as needles between infected and healthy horses.

There is no treatment or vaccine for EIA, and infection is life-long. Owners of infected horses in many U.S. states have two unappealing choices: Quarantine the horse at least 200 yards away from all other horses for the rest of his life, or euthanize him. Many opt for the latter.

EIA By the Numbers

The good news is that extensive testing and euthanasia of infected horses over the last 40 years have made the outbreaks