Equine Infectious Anemia (EIA) is a systemic virus infection of horses, donkeys, their crossbreeds, and zebras. The causative agent, a lentivirus from the family of retroviruses, replicates in monocytes and macrophages and causes lifelong persistent infection accompanied by more or less severe immunopathological processes.
The disease is notifiable and is regimented in Germany by the „regulation for protection against equine infectious anemia“ (2000, Federal Law Gazette I p. 531) which imposes mandatory culling of positive animals as well as movement bans and testing of affected and contact holdings. Immunoprophylaxis is not available. A risk for humans does not exist.
EIA occurs worldwide and is reported in larger numbers in North and South America, Africa, Asia, Australia, and in Southern and Eastern Europe. In Northern and Central Europe, sporadic cases are registered. The virus is not endemic in Germany, isolated outbreaks however occur repeatedly. In most cases so far, an association with imported horses could be established.
Mechanic transmission by large sanguivorous insects such as the dark giant horsefly and the stable fly (Tabanus, Stomoxys) is of epidemiologically relevant significance. Attached to the mouthparts of insects, EIAV remains infectious for not more than 30 minutes; therefore insect vectors do not spread the virus over longer distances. Infected horses excrete EIAV with body secretions such as saliva, milk and semen which may also be a transmission route, if animals are kept in close contact with each other. EIAV can also be transmitted by certified biological products or by veterinary instruments or grooming equipment, if disinfection and hygienic measures are neglected.
Infected animals remain lifelong virus carriers and are potential sources of infection. In many cases the name-giving anemia, which is caused by the immunopathological destruction of red blood cells, is not observed. 30 to 90 % of infected animals are asymptomatic, the animals remain healthy-looking virus carriers, so-called asymptomatic carriers.
Clinical disease can manifest in an acute or chronic form, in isolated cases with fatal outcome. Clinical episodes usually last 3 to 5 days and are accompanied by recurrent febrile episodes.
The acute course of disease is characterized by fever, apathy, as well as petechiae especially on the underside of the tongue and on mucous membranes and palpebral conjunctiva. Chronic courses are characterized by acute episodes of disease with recurrent fever, fatigue and edema.