Equine infectious anemia (EIA) is a disease caused by a virus that produces anemia, intermittent fever, and severe weight loss. Equidae (e.g., horses, ponies, mules, and donkeys) are the only animals known to be affected by the virus. Once an animal is infected with the virus it is infected for life, regardless of the severity of the symptoms.  No treatment is effective against the EIA virus.

When the virus enters the bloodstream, it invades lymphocytes (a form of white blood cells that are important in the body's defense against disease). The virus then reproduces in the lymphocyte, increasing in numbers until the lymphocyte bursts, releasing more virus into the bloodstream to repeat the cycle. The animal attempts to fight off the viral infection by producing antibodies against the virus. However, this antibody is not effective in eliminating the virus from the body, and enough lymphocytes are destroyed over time to reduce the effectiveness of the immune system. When the animal reaches this stage, it usually succumbs to other bacterial or viral infection. The death rate of infected Equidae varies from 30 to 70 percent, and is usually higher when the virus is introduced into a new geographical region.

The anemia that sometimes accompanies this disease is caused by the animal's immune system attacking the cells that produce red blood cells in the bone marrow. The reasons for this event are unknown.

Other common names for EIA are: swamp fever, mountain fever, slow fever, and Coggins' disease.

More about Equine Infectious Anemia