Patterns of EIA

Standing horse in black and white.

Initial signs of EIA may include: an intermittent or continuous fever (sudden rise from 100 degrees Fahrenheit to 105 degrees Fahrenheit), profuse sweating, rapid breathing, depression, and weight loss (even though the animal continues to eat well). Disease signs occur 7 to 21 days after primary infection.

The initial signs of EIA pass quickly into one of four patterns: acute, subacute, chronic, or carrier.  

  1. Acute cases are more the exception than the rule. These animals rarely survive and can die within 3 to 10 days after the virus enters the bloodstream.
  2. Subacute cases can also be very sick and then become chronic. These animals exhibit no signs of the disease for a long time, then progress to a state of continuing weight loss, rough hair coat, and anemia. Relapses of increasing severity are common.
  3. Chronic cases may have occasional attacks and develop classic symptoms which can include a poor hair coat, weight loss, weakness, anemia, and swelling of the lower legs, chest, and abdomen. These signs will later subside, but may never recur. These symptoms commonly develop after stress from hard work, hot weather, pregnancy, or from other diseases.
  4. Carrier animals appear to be healthy, but harbor the agent of the disease. An animal will carry the virus for its entire life and never show signs of the disease, but it is potentially able to transmit the disease. These animals may develop into acute or chronic cases after hard work, severe stress, or from other diseases.