A presumptive diagnosis of ECE may be made on the basis of typical clinical signs. Confirmation can be made on the basis of paired serology (rising EHV-3 antibodies in clotted blood samples) with samples collected at the time of first suspicion and 14–21 days later, and tested for EHV-3 neutralising (VN) antibody1. A fourfold or greater rise in antibody level between the first (acute) and second (convalescent) samples usually confirms recent EHV-3 activity. ECE cannot be conclusively ruled out on the basis of less than a four-fold rise in antibody titre as VN antibody production may be lower in some cases.
Confirmation of diagnosis may also be made on the basis of isolation of EHV-3 from active lesions, although care should be taken that failure to isolate virus does not necessarily preclude that infection has occurred recently.