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Equine Infectious Anemia (EIA) and the Coggins Test
Equine Infectious Anemia (EIA) and the Coggin's or Coggins Test in Horses
Introduction
Equine Infectious Anemia is a viral disease of horses for which there is no cure, nor is there a vaccine to prevent this disease. Equine infectious anemia is a disease of horses characterized by three clinically distinct forms. These range from a rapidly worsening febrile disease that results in death to a chronic carrier form that appears outwardly healthy . First described more than 150 years ago in Europe, the disease has been seen in the United States for more than 75 years. In 1970 an agar-gel immunodiffusion (AGID) test, the Coggins test, capable of detecting unapparent virus carriers. This test, along with improved knowledge about EIAV transmission, has made effective control of the infection among horse populations a reality. This article discusses how horses get this disease, clinical signs, testing for EIA and its reliability, and the handling of infected horses.
Clinical Signs
The incubation period following inoculation is usually between one and four weeks but can be as long as two or three months. Experiments currently indicate that donkeys, while contracting the disease, do not become clinically ill. Their role in infecting other horses is uncertain. Infectious anemia may appear in an acute, subacute, or chronic form. The acute form occurs most often when EIAV is first introduced into a susceptible group of horses. The rate of infection is extremely variable but can approach 100 percent in susceptible populations. Severity of initial infection can vary from mild to mortality rates as high as 30 percent of those infected. The reason for this variability is uncertain but different strains with different pathogenicity is conjectured. Mortality rises during hot weather.
Acute
The prominent acute clinical signs are:
- fever
- profuse sweating if hot
- depression
- loss of appetite
- serous nasal discharge
- rapid weight loss
- severe hemolytic anemia
- dependent edema
Chronic-recurring
The chronic form of the disease consists of a series of short acute attacks, between which the intervals of good health may be quite long lasting months or even years. During periods of good health the amount of virus in the blood stream is very low so these animals are a small risk until their next subacute onset of illnesses. However such animals may develop anemia and hypergammaglobulinemia though appearing healthy. The heart beat becomes irregular, and edema and weakness may occur between healthy episodes. Chronic weight loss in the face of a good appetite is occasionally a feature and such animals have been kept under careful observation for many years, during which time their blood has been found to be continuously infective for susceptible horses.
Chronic-inapparent
In the inapparent form horses can remain infected but free of clinical signs for years. During these periods the horse appears healthy and is of very low infectivity. Usually with time however, these horses begin to have acute attacks, become infective, and eventually succumb to the disease.
Transmission
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