Equine Infectious Anaemia (EIA), also known as malarial fever, mountain fever, slow fever, or swamp fever, is a viral disease of horses causing intermittent fever, anemia, emaciation (extreme weight loss) and death. It can be transmitted by mechanical transfer of blood by biting insects and occurs typically in low-lying swampy areas. Equine Infectious Anemia Virus (EIAV) is a lentivirus, of the Retrovirus family with an almost worldwide distribution, infecting equids - horses, mules and donkeys. The EIAV belongs to the family of RNA viruses which generally cause slowly progressive, often fatal diseases. The virus is closely related to the human immunodeficiency virus (HIV), which causes acquired immunodeficiency syndrome (AIDS) in humans. Animals may be acutely or chronically infected. The incubation period is variable, from a matter of days to a few months but generally 1 to 3 weeks. Antibodies usually develop 7 to 14 days after infection and last for life. Infected animals remain carriers of the virus for life. Equine infectious anemia is considered a classic bloodborne infection. People have played an important role in EIAV transmission over the years by using blood-contaminated materials on different horses. The EIAV most frequently is transmitted between horses in close proximity by large biting insects, such as horseflies and deerflies.
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The clinical signs of the acute form of equine infectious anemia are nonspecific; in mild cases, the initial fever may be short lived (often 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.
The majority of horses are inapparent carriers: they show no visible abnormalities as a result of infection. The inapparent form may become chronic or acute due to severe stress, hard work, or the presence of other diseases.
Symptoms of acute form depend upon the stage of the disease. Bleeding, edemas (excessive accumulation of fluids in body tissues or cavities), rapid breathing, and jaundice occur in the acute disease. During the attack, which usually lasts three to five days, the animal will try to shift its weight from one leg to another because of weakness. It will have shaggy coat and be sluggish.
If the horse survives this first acute bout, it may develop enlargement of the liver, spleen and lymph nodes, anemia, fever, different sizes of bleeding into the skin (petechia), an irregular heartbeat, and a jugular pulse may become evident.
Control of equine infectious anemia is currently based on detection of anti-EIA virus (EIAV) antibodies through AGID test. However, the current diagnostic methods may fail to diagnose the disease at its early stage. infection. There is no vaccine or treatment for the disease. It is often difficult to differentiate from other fever-producing diseases, including anthrax, influenza, and equine encephalitis. For more information on equine infectious anemia please visit USDA, APHIS, Veterinary Services