It’s been nearly a week since the first indications of a neurologic equine herpesvirus-1 (EHV-1) outbreak began to surface, and the outbreak shows no signs of slowing down. Veterinarians have been confirming new cases of neurologic EHV-1 daily in the western United States and Canada. The National Cutting Horse Association’s (NCHA) Western National Championship competition, held April 28-May 8 in Ogden, Utah, has been identified as a common denominator in the outbreak, as many of the horses confirmed or suspected of having the disease were involved in the competition or exposed to horses coming home from the event.

Equine herpesvirus-1 is highly contagious and can cause a variety of ailments in horses, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and myeloencephalopathy (evident in the neurologic form). The virus is not transmissible to humans. Clinical signs of EHV-1 myeloencephalopathy include fever, ataxia (incoordination), weakness or paralysis of the hind limbs, and incontinence. The virus is generally passed from horse to horse via aerosol transmission (when affected animals sneeze/cough) and contact with nasal secretions.

As veterinarians and horse owners work to control the outbreak, updated case numbers from Western states continue to emerge. At press time, the most up-to-date numbers from individual states are as follows:

Arizona – In a press release issued Wednesday (May 18), the Arizona Department of Agriculture indicated that one horse had tested positive for neurologic EHV-1