The neurologic form of equine herpesvirus type-1 (EHV-1) has been confirmed as the cause of disease in two Maryland horses infected during a deadly disease outbreak this spring. Twelve horses exhibited signs of neurologic illness in the outbreak at a single Montgomery County farm, five of which died. While the virus has not been confirmed in the other 10 horses, EHV-1 is suspected.

According to Amy Polkes, DVM, Dipl. ACVIM, one of the veterinarians involved in the case, it took several weeks of extensive testing at multiple laboratories to make the confirmation, which was announced July 8. The confirmations were made using samples from a deceased horse and one that survived.

The first signs of illness were detected in March, and the Maryland Department of Agriculture put the farm under quarantine. Veterinarians are confident the disease was contained, and the quarantine was lifted June 23 after five weeks passed with no additional cases of neurologic disease.  (For more information on the outbreak, click here.)

Polkes says no one is sure how EHV-1 was introduced to the farm, which houses mainly polo horses. “It’s one of those contagious diseases that is usually seen as the respiratory form, and there’s no way that we could track it back to exactly how these horses got it