Equine infectious anaemia

Equine infectious anaemia (EIA) is a persistent viral infection of equids. The causative agent, EIA virus (EIAV) is a lentivirus in the family Retroviridae, subfamily Orthoretrovirinae. Other members of the genus Lentivirus include: bovine immunodeficiency virus; caprine arthritis encephalitis virus; feline immunodeficiency virus; human immunodeficiency virus 1; human immunodeficiency virus 2; and maedi/visna virus. EIA can be diagnosed on the basis of clinical signs, pathological lesions, serology and molecular methods. Infected horses remain viraemic carriers for life and, with very rare exceptions, yield a positive serological test result. Antibody response usually persists and antibody-positive animals, older than 6–8 months, are identified as virus carriers (below 6–8 months of age, serological reactions can be due to maternal antibodies; status can be confirmed by molecular techniques). Infected equids are potential virus reservoirs. Biting flies are mechanical vectors for the virus in nature.