Signs are usually most severe in very young, very old or debilitated horses. Epidemics can occur where horses are congregated. EVA is transmitted by aerosolized nasal secretions and by venereal spread. A carrier state can develop in stallions with the virus present in semen. There is no specific treatment.
Supportive treatment is useful where indicated.
Laboratory diagnosis is made by virus isolation or serum neutralization blood testing. Virus can be isolated from nasopharyngeal and conjunctival swabs, citrated blood samples or semen. Breed infected stallion two times a day for two to four days each to two seronegative test mares. Isolate test mares and blood test on day 14 and day 28 following last cover. If mares remain serologically negative, stallion may be registered.