Equine Infectious Anemia (EIA)

​Disease Basics

EIA (or swamp fever) is an infectious and potentially fatal viral disease of horses usually transmitted from horse to horse by large biting insects such as horseflies and deerflies. Needles and equipment contaminated with blood from an infected horse can also spread the virus when used on unexposed horses. No vaccine or treatment exists for the disease. Some equines can be infected with the virus and act as carriers, but do not show any signs. It is a reportable and actionable disease.  


Minimizing or eliminating contact between non-exposed horses and the secretions, excretions, and blood of infected horses can help control the spread. ​Insect control is another method for preventing the transmission of the virus.

Clinical Signs of Illness

Horses that are infected with the virus experience fever, weight loss, yellowing of body tissues, anemia, swelling in the limbs and weakness.  


The Coggins test, or agar-gel immunodiffusion test, is internationally recognized as the standard to which all other tests are compared for diagnosing EIA. EIA testing requirements apply to all equines, including donkeys, mules, zebras and wild horses/asses.

Review the U.S. Department of Agriculture (USDA) Approval of Laboratories to Conduct Tests for EIA to learn how a laboratory receives approval to test for the disease. The USDA also offers ancillary resources clarifying the procedures for approval and addressing frequently asked questions.

Testing Requirements

​See the "moving horses and other equines within Wisconsin" section of the horses & other equine movement​ webpage.

Huma​​n Health

There is no known human health impact caused by EIA.