An outbreak of equine herpesvirus-1 in the western U.S. and Canada has put public health officials and horse owners on alert this spring.
The outbreak apparently originated at the National Cutting Horse Association Western National Championships, held April 29-May 8 in Ogden, Utah. In the weeks following the event, cases of EHV-1 infection and equine herpesvirus myeloencephalopathy were confirmed in horses in nine states and Alberta, Canada, that either had been at the championship or had been in contact with horses exposed at the event.
The Department of Agriculture is working with state and federal animal health officials and private equine practitioners to collect information on affected horses and develop a coordinated response among state, federal, and industry partners. A complete accounting of the full scope of the EHV-1 outbreak and the numbers of affected and exposed horses was under way at press time.
As of June 2, a total of 2,093 horses were reported to have been exposed to EHV-1, 52 cases of EHV-1 infection and 32 cases of EHM had been confirmed, and 12 horses had died or been euthanized, according to a situation report by the USDA Animal and Plant Health Inspection Service's Veterinary Services.
Practitioners are encouraged to notify state animal health officials of suspected and confirmed cases of EHV-1 and EHM. The USDA also urges horse owners and organizations to take action to mitigate the potential for viral transmission.
As of press time, the outbreak had caused the cancellation or postponement of numerous equestrian events throughout the West. Colorado, North Dakota, Washington, and Wyoming had implemented new travel requirements for any horses entering their states. The veterinary teaching hospitals at Colorado State University and Washington State University had closed to nonemergency equine and camelid patients.
Practitioners are encouraged to notify state animal health officials of suspected and confirmed cases of EHV-1 and EHM.
EHV-1 can cause neurologic damage, respiratory problems, abortion, and neonatal death in horses and camelids. Although many animals may carry the virus, it usually remains inactive until triggered by stress, such as that associated with excessive exercise, long-distance transport, or weaning.
EHV-1 is the primary cause of EHM, which is considered an emerging disease that causes damage to the blood vessels in the brain and spinal cord and can be fatal. However, not all infected horses will develop EHM.
Signs of EHM in horses may include nasal discharge, incoordination, hind limb weakness, lethargy, urine dribbling, and decreased tail tone. Currently, there is no vaccine that protects against EHM, nor is there a specific, proven treatment.
The American Association of Equine Practitioners has developed resources about EHV-1, EHM, and the current outbreak, including updates and FAQs for veterinarians and other resources for horse owners, available at www.aaep.org.