The neurologic disease equine herpesvirus myeloencephalophy (EHM), which is caused by equine herpesvirus-1 (EHV-1), has been in the news recently with horses and farms affected across the United States and Canada. The outbreak appears related to initial cases at a cutting horse show in Ogden, Utah, which was held April 29-May 8. While the true extent of the outbreak is unclear at this time, there is an elevated risk of EHM cases in horses that were at the show or in contact with horses that were at the show. Pfizer Animal Health encourages anyone with questions or concerns about the disease to contact their local veterinarian.

Equine herpesvirus-1 (rhinopneumonitis) also causes upper respiratory infections in horses and abortions in pregnant mares. However the neurologic disease (EHM) affects the horse’s brain and spinal cord and can result in paralysis and death. Clinical signs include incoordination (ataxia) that can progress to the inability to stand, lower leg swelling, the inability to urinate or pass manure, urine dribble, and reduced tail tone. Some of the symptoms of EHM can be confused with other neurologic diseases such as rabies, equine protozoal myeloencephalitis (EPM), and West Nile virus, so it is important for a veterinarian to examine animals showing any clinical signs as soon as possible.

The EHM virus is the most infrequent and potentially devastating form of EHV-1 infections and is difficult to treat once neurologic symptoms are observed.

"It’s important for horse owners to understand the facts about the disease," said Tom Lenz, DVM, MS, Dipl. ACT, senior director of equine veterinary services for Pfizer Animal Health. "EHV is extremely contagious, and many horses may become latently infected-infecting other horses but may never display symptoms themselves. Working with a local veterinarian to develop a comprehensive disease prevention program including good barn hygiene is the best defense horse owners can provide their animals