Transmission of
Equine Infectious Anemia Virus

Transmission of Equine Infectious Anemia virus occurs almost exclusively via a mechanical vector containing contaminated blood or blood product

The most common vector are biting insects (mouthparts) that transfer the infection from one contaminated horse to an uninfected horse.
Other sources of transmission include:
It is also notable that EIA is not shed via urine or saliva (2)
Only 1 of every 6 million flies is likely to become a vector (2). Of these insects, the most common mechanical vectors include the stable fly (Stomoxys calcitrans) and the biting flies: horse flies (Tabanus spp. and Hybomitra spp.) and deer flies (Chrysops spp) (2,3,5). As the fly bites one horse, the horse's reaction to the noxious bite will interrupt the fly's feeding, and will therefore re-attempt to bite the same horse, or will then move on to bite another horse with its newly infected mouthparts.