Equine infectious anemia, or EIA, is an incurable, infectious disease caused by a virus. Horses, ponies, donkeys, asses and other equine family members are vulnerable. Other common names for the disease include swamp fever, mountain fever or malarial fever.
Studies show as few as three horseflies can carry the virus from one animal to another.
Acute responses generally occur 7 days to 30 days after initial exposure. Horses may develop fever, go off feed, or die suddenly. Eventually, the virus destroys red blood cells, causing severe anemia. Equine in the acute stage may test negative for 16 days to 42 days after exposure, until the animal's immune system has had time to produce detectable antibodies. Symptoms will subside, but may reoccur.