Cause
The causative agent of EIA is the equine infectious anemia virus, or EIAV, a lentivirus of the family Retroviridae. Blood-feeding horseflies and deerflies transmit this virus as the primary vectors, or carriers. Venereal transmission is possible, but unlikely. EIAV can be transmitted to the fetus before birth and to the neonate through colostrum/milk from an infected dam. Iatrogenic transmission can also occur via contaminated needles, syringes, and surgical instruments, as well as through transfusion of contaminated blood. Once infected, a horse remains infected for life, serving as a potential source of infection to other horses. The virus does not infect other non-equid animals or people.