Equine Herpesvirus 1 (EHV-1), Equine Herpesvirus Myeloencephalopathy (EHM) by Amy Young, Dr. Nicola Pusterla, and Dr. Katie Flynn July 31, 2019 Equine herpesvirus-1 is a virus that causes potentially serious disease in horses. The neurological form can cause Equine Herpesvirus Myeloencephalopathy.