EAV infects cell cultures derived from various animals, e.g., horse, cat, hamster, rabbit, pig and monkey. The cytopathic changes include cell rounding, vacuolisation, shrinking, and detachment from the growth surface. The infection may cause panvasculitis with virus replication and lesions occurring in most parts of the cardiovascular system. Viraemia develops and the virus can be found in practically all body fluids and tissues, with the exception of the brain. The outcome of infection with EAV is determined by the strain and infectious dose of the virus, the age and physiological condition of the infected horse, the environmental conditions and the route of infection.
Natural infections are frequently asymptomatic.
Although naturally infected horses usually recover after cessation of viraemia, death as a result of progressive interstitial pneumonia has been reported in very young and adolescent foals. Occasionally, infection of pregnant mares may result in abortion, which can occur 10 - 30 days after virus infection even if no clinical signs are noted in the mare. The infected mares may abort without showing any other clinical signs. Infection of stallions may result in a period of subfertility as a result of a decrease in the production of normal sperm cells for 3-4 months after infection. Stallions may become persistent carriers of the virus, and transmit the infection venereally to mares.