The variety and severity of clinical signs of EVA vary widely. Infection may be obvious but there may be no signs at all. Even when there are no signs, infection can still be transmitted and stallions might still ‘shed’ the virus, ie excrete it in their semen. These stallions are known as ‘shedders’ and pose a significant risk of disease transmission if undetected. In pregnant mares, abortion may occur. EVA may, occasionally, be fatal.
The main signs of EVA are fever, lethargy, depression, swelling of the lower legs, conjunctivitis (‘pink eye’), swelling around the eye socket, nasal discharge, ‘nettle rash’ and swelling of the scrotum and mammary gland.