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Veterinary Medical Teaching Hospital Update on Equine Herpesvirus-1 (EHV-1)

The following update was prepared by faculty of the Equine Medicine Service at the William R. Pritchard Veterinary Medical Teaching Hospital. The Large Animal Clinic remains open to equine patients and for other client services. See related story of May 17, 2011.

May 19, 2011

Two more horses in California have tested positive for EHV-1. They are both located in Corning, California, and they have not been seen or admitted to the Veterinary Medical Teaching Hospital. These horses are cutting horses that have an exposure link to the National Cutting Horse Association’s Western National Championships (NCHA) that was held at the Golden Spike Event Center in Ogden, Utah from April 29th to May 8th.

Recently, two horses were hospitalized in the Large Animal Clinic Isolation Facility and they are gradually improving. There are NO equine herpes cases in the main clinic, which is physically separated from the Isolation Facility. We have tested all horses admitted to the clinic this past week, and all of them have tested negative. We will continue to monitor and test all horses admitted to the clinic to ensure maximal biosecurity safety of our hospital. With these heightened biosecurity and surveillance measures in place to protect our patients, the VMTH equine clinic remains open for full patient receiving and emergency services. 

Suggested Guidelines for Minimizing Risk of Disease Transmission:

  • Restrict movement of horses from the premises.
  • Physically isolate exposed horses a minimum of 30 feet away from other horses for 21 days.
  • Horses that are new to premises should also be isolated, as above.
  • If you suspect a horse may have been exposed, then monitor the horse’s rectal temperature twice a day for 14 days and call your veterinarian immediately if a fever develops (≥ 102 ºF).
  • Use protective barrier clothing that can be changed in between horses when handling isolated or quarantined horses. Protective barrier clothing includes: gloves, disinfectant foot baths with impervious foot covers, and coveralls or protective gowns. Hands should be washed with soap and water or alcohol based hand sanitizers (if visibly soiled, hands must be washed with soap first) after handling each horse in quarantine.
  • Provide separate equipment for each horse and do not share buckets, feeders, tack, grooming equipment, towels etc among horses. 
  • When filling water buckets, make sure the end of the hose does not touch the water in the bucket in order to avoid contamination with infectious material that may be on the outside of the hose.
  • Potential inanimate fomites such as buckets or tack, if used on more than one horse, should be disinfected before use on another horse. NOTE: The equine herpesvirus is susceptible to many disinfectants; however, whenever organic matter is present, washing and removal of organic material should be done first. If organic matter persists, use disinfectants suitable for use in the presence of organic matter, such as higher peroxygen compounds (e.g.-Trifectant, Virkon) or phenolics (e.g.-Tek-Trol or 1-Stroke Environ).
  • Consider vaccinating at risk healthy, afebrile horses on the premises to which exposed horses are returning. Consult your veterinarian for vaccination recommendations.

For additional information, please refer to the following sites:

May 17, 2011 Equine herpesvirus in California

California Animal Health and Food Safety Laboratory (testing services)

UC Davis School of Veterinary Medicine Real-Time PCR Research and Diagnostics Core Facility  (PCR testing services)

UC Davis Center for Equine Health

CDFA Equine Herpes Alert May 13th and updates


CDFA Equine Herpes Myeloencephalopathy Fact Sheet

USDA Resources: Equine Herpes Myeloencephalopathy Brochure

American Association of Equine Practitioners Fact Sheet


W. David Wilson, BVMS, MS, director, William R. Pritchard Veterinary Medical Teaching Hospital

K. Gary Magdesian, DVM, DACVIM, DACVECC, DACVCP, associate professor, equine critical care