Equine infectious anemia is a persistent disease in horses and other equids, and can eventually be fatal. The aetiological agent of EIA is equine infectious anemia virus (EIAV) and it belongs to the family Retroviridae, to the Lentivirus genus. It is a positive single stranded RNA virus that uses a reverse transcriptase, encoded in the viral genome, to produce DNA that is incorporated into the genetic makeup of infected cells. The disease is present in three forms, acute, chronic and inapparent.