Because of the variability or the possible absence of signs of EVA, clinical diagnosis is not always possible. Laboratory diagnosis is therefore essential. Laboratories can identify the presence and level of antibodies to the virus by testing blood, and can screen for the actual virus in blood and other samples. Laboratories generally require blood serum for antibody detection and heparinised or EDTA blood (preferably heparinised) or semen for virus detection. Other samples may be required. If in doubt, veterinary surgeons should check with the laboratory.
Where abortion or newborn foal death may be EVA-related, a detailed clinical history of the mare must be sent to the laboratory immediately, together with blood samples from the mare, samples of the placenta and the fetus or carcase for specific examination for the EAV.