Equine infectious anemia virus (EIAV) is a member of the Lentivirus genus in the family Retroviridae and infects only members of the Equidae (including horses, donkeys, and mules). Equine infectious anemia (EIA), also known as “swamp fever”, is an important infectious disease of horses caused by EIAV and is characterized by recurrent episodes of fever, lethargy, inappetence, thrombocytopenia, and anemia. EIAV has a genomic organization similar to that of other lentiviruses, such as human immunodeficiency virus type 1 (HIV-1), maedi-visna virus (MVV), or caprine arthritis encephalitis virus (CAEV). EIAV infection is associated with an initial dynamic disease, after which most horses infected with EIAV are able to control viral replication and become asymptomatic carriers for life. However, carriers can still transmit the virus, and clinical signs of EIA can recur in carriers when the immune system is suppressed naturally or experimentally. An attenuated EIAV vaccine was successfully developed in China in the 1970s using classical serial passage techniques. This vaccine is the first and only attenuated lentivirus vaccine, and has been widely used in China. As a result, EIAV has been regarded as a useful model for studying the dynamic interactions of lentiviruses with host immune responses during viral replication.