Animal HealthDiseasesEquine Infectious AnemiaSigns and Symptoms

Equine Infectious Anemia (EIA) Signs and Symptoms

A list of clinical signs the animal may or may not display.


Signs and Symptoms of EIA can be broken down into three categories:

  1. Acute
    The horse develops severe signs and dies within 2 to 3 weeks. The signs appear very rapidly and may include only an elevated body temperature that may be short lived (less than 24 hours). As a result, horse owners and veterinarians may not observe this initial sign when a horse is infected with EIAV. These infected horses often recover and continue to move freely in the population. The first indication that a horse was exposed to, and infected with, EIAV may well be a positive result on a routine annual test. One–fifth of a teaspoon of blood from a horse with acute EIA contains enough virus to infect 1 million horses.
  2. Chronic
    If the horse survives this first acute bout, it may develop a recurring clinical disease with these signs:
    • Fever
    • Petechial hemorrhages (minute blood–colored spots on mucous membranes).
    • Depression (listless, head hangs low)
    • Weight loss
    • Dependent edema (swelling of fluid collecting under the skin in the legs and under the chest and other underbody surfaces).
    • Anemia (drop in its red corpuscle count and appear thin and watery. The animal may also have an irregular heartbeat, and a jugular pulse may become evident.
    • One fifth of a tea spoon of blood from a chronic case during a feverish episode contains enough virus to infect 10,000 horses.
  3. Unapparent
    By far the majority of horses are inapparent carriers: they show no overt clinical abnormalities as a result of infection. They survive as reservoirs of the infection for extended periods. Inapparent carriers have dramatically lower concentrations of EIAV in their blood than horses with active clinical signs of the disease. Only 1 horsefly out of 6 million is likely to pick up and transmit EIAV from this horse. All horses infected with EIAV are thought to remain virus carriers for life. The inapparent form may become chronic or acute due to severe stress, hard work, or the presence of other diseases.

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Helena, MT 59620-2001
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