Equine herpes myeloencephalopathy (EHM), caused by Equine herpes virus (EHV-1), has been confirmed in 10 horses in California, in Kern, Placer, Stanislaus, Amador and Napa counties.

One horse in Kern County was euthanized after showing severe neurologic signs often associated with the disease. All of the infected horses recently attended the National Cutting Horse Association’s Western National Championships in Odgen, Utah on April 30 – May 8, 2011, where they were most likely exposed to the virus.  All California horses that have been in contact with an infected horse and show signs of disease or test positive for EHM will be placed under a CDFA quarantine in order to limit spread.  This disease outbreak is evolving and CDFA will continue to investigate cases and provide updated information.

The California Department of Food and Agriculture has contacted all 54 exhibitors from California who participated in the Odgen, Utah event and asked them to isolate and monitor their horses for clinical signs of EHV-1.  A rectal temperature in excess of 102 F commonly precedes other clinical signs.  Therefore, horse owners with potentially exposed horses are urged to take temperatures on each individual horse twice a day.  If a temperature above 102 F is detected, the horse’s private veterinarian should be contacted immediately for evaluation and laboratory testing. 

Equine herpes virus is a contagious disease and may spread quickly among horse populations. EHV-1 is not transmissible to humans. Horse-to-horse contact, aerosol transmission, and contaminated hands, equipment, tack and feed all play a role in disease spread.  Horses infected with the neurologic strain of EHV-1, may show any of the following clinical signs:  nasal discharge, lack of coordination, hind-end weakness, lethargy, urine dribbling and diminished tail tone.  There is no specific treatment for EHM.  Treatment may include intravenous fluids, anti-inflammatory drugs and other appropriate supportive treatment.  Immediate separation and isolation of identified suspect cases and implementation of appropriate biosecurity measures are key elements for disease control.  Currently, there is no equine vaccine that has a label claim for protection against the neurologic strain of this virus.