Systematic Veterinary Virology

SYMPTOMS

• The first attack is usually the most acute with the horse suffering from depression, profound weakness, and loss of condition. Intermittent fever with large and rapid swings in temperature may also occur. Jaundice and bleeding around the mouth and nasal areas may also occur. This form of the disease is the most damaging and the most difficult to diagnose because the signs appear rapidly, and often only an elevated body temperature is noted. One–fifth of a teaspoon of blood from a horse with acute EIA contains enough virus to infect 1 million horses.
•  Animals may show a temporary recovery and appear normal for 2 - 3 weeks and then relapse with similar, but less sever symptoms. It is also referred as chronic form. The symptoms include fever, petechial hemorrhages on the mucous membranes, depression, weight loss, dependent edema under the skin in the legs and under the chest and other underbody surfaces and anemia. The animal may also have an irregular heartbeat, and a jugular pulse. One fifth of a tea spoon of blood from a chronic case during a feverish episode contains enough virus to infect 10,000 horses.
• Most horses also remain as inapparent carriers. These horses show no obvious clinical signsas 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.