Veterinarians have confirmed equine herpesvirus myeloencephalopathy (EHM, the neurologic form of equine herpesvirus-1, or EHV-1) in a well-known Bowman County barrel racing horse.

The horse developed signs of disease on Thursday, April 19. The disease progressed rapidly, and the veterinarians euthanized the horse the same day. Confirmatory lab results were received Friday evening, the North Dakota Department of Agriculture said in an April 23 statement.

Horses exposed to the positive horse within 72 hours prior to the onset of clinical illness have been quarantined. Owners of other horses that might have had contact with the affected horse prior to that period are being advised to consult with their local veterinarian, monitor their horses for signs of disease, and restrict travel.

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and EHM. In many horses, the only sign of EHV-1 infection is fever, which can go undetected.

In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months) but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.

Horses with the neurologic form usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.

Vaccines are available for the respiratory and reproductive forms of EHV-1. They do not reliably protect against EHM, but might offer some level of protection.

“With summer coming, many horses will be moving to events around the region,” said State Veterinarian Susan Keller, DVM. “Care should be taken when commingling horses to minimize the chances of contracting the disease.”

Equine herpesvirus can spread through the air, contaminated equipment, clothing, and hands. Biosecurity measures that can reduce the risk of spreading the disease include avoiding shared food or water containers and preventing nose-to-nose contact.

Out-of-state horses and other equines entering North Dakota for any length of time must be accompanied by a certificate of veterinary inspection.

“Certificates of veterinary inspection reduce the risk of introduction of clinical disease and help us better monitor the movement of equines into North Dakota,” said Keller. “We use that information to report disease risks and findings to veterinarians and horse owners in North Dakota.”