Infection of a susceptible equid occurs exclusively as a result of the spread of EIAV contaminated blood or blood products from an infected horse, donkey or mule. This includes clinically normal animals as well as persistently infected animals. Rapid spread of the virus can occur when susceptible animals come in contact with clinically affected animals that have high concentrations of virus in their blood.

   horse with her foalhorse grazing1

In natural settings, the transfer from infected animal(s) to susceptible animal(s) is most often via: 


a)      Biting insects by mechanical transmission.

b)      Intrauterine infection which results in abortion or death of the foal by two months of age.

c)      Use of contaminated surgical instruments/needles with the subsequent injection of small quantities of virus.

d)      Untreated biological preparations of equine origin in enzootic areas.

e)      Virus invasion through intact oral and nasal mucosa, wounds and even unbroken skin (minor importance in field outbreaks).

f)        Semen from an infected stallion.