Equine Infectious Anemia

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Infection Anemia in Horses

Sometimes referred to as horse malaria or swamp fever, Equine Infectious Anemia (EIA) is a virus that causes destruction of the horse’s red blood cells, causing anemia, weakness, and death. EIA has become endemic in certain parts of the world, but is very uncommon in the United States. In fact, EIA is a reportable disease in the U.S., which means that if it is diagnosed in a horse in this country, the veterinarian is required to notify the USDA.

There is no cure for Equine Infectious Anemia. It is spread by the horsefly. Horses are required to be tested for this disease for entry into shows and for transport across state lines. This is a simple routine blood test called a Coggins test.


EIA can present as an acute form or chronic form. The acute form is usually fatal. If the horse survives, it will become a chronic carrier of the disease. Once infected, the virus remains in the horse’s body for the rest of its life. Chronic carries are referred to as “swampers”.

  • Anemia
  • Lethargy
  • Weight loss
  • Fever
  • Enlarged spleen
  • Swollen belly and legs (edema)
  • Depression
  • Decreased athletic performance
  • Death (in acute cases)


EIA is caused by a retro virus and transmitted by horseflies. However, the infection can also be spread through blood-contaminated items such as unsterilized needles, syringes, etc.


Your veterinarian will usually conduct a Coggins test on the suspected animal, which is a laboratory-run blood test to diagnose EIA in horses.


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