EVH-1 Press Conference Summary

Pilchuck Veterinary Hospital EHV-1 Press Conference Summary

Friday, May 20, 2011

Comments by Wendy Harless Mollat, DVM, Diplomate ACVIM, Equine Internist, Critical Care and Neonatology Specialist

We’re here today to provide updated information on the latest outbreak of Equine Herpes virus 1 (EHV-1).

 EHV-1 is widespread within the equine population. Veterinarians have been dealing with EHV-1 outbreaks similar to the current one since 2003. Pilchuck treated another EHV-1 positive case in their isolation facility three years ago.

Most horses are infected with this virus by the time they are 2 years old. Just like in humans, the herpes virus remains dormant in nerve terminals. Stress can cause the herpes virus in humans to reactivate, showing up as cold sores. Horses under stress – such as those traveling across the country for shows – also can have their virus reactivated.

EHV-1 has always been known to have the ability to cause neurological disease, but rarely caused outbreaks. In 2003, a genetic mutation of EHV-1 was identified in a large neurological disease outbreak in Ohio. This newer strain causes more severe neurological signs than the original varient.

All horse breeds can contract EHV-1. There is no risk to humans. Alpacas and llamas may contract EHV-1, however.

Statistics as of May 20, 2011

Note: We are able to get a good idea of which horses have been exposed due to the requirement of horse health certificates to cross state lines. The AAEP and USDA are closely monitoring EHV-1 reports (http://www.aphis.usda.gov/vs/nahss/equine/ehv/).

  • 308 horses were exposed at the National Cutting Horse Association Western National Championship in Ogden, Utah, held April 29-May 8.
  • 689 horses were exposed to the Utah horses once they traveled back to their home barns.
  • Of these horses, 21 cases of EHV-1 have been confirmed, either by blood test or nasal swab test. Only 12 of these cases developed neurological signs of the virus.
  • Seven horses have died.
  • Nationally, 174 barns and facilities are under voluntary quarantine.
  • There are five confirmed EHV-1-positive cases in Washington state.
  • One of these cases is at Pilchuck under quarantine in its isolation facility.
  • Pilchuck Veterinary Hospital remains open for regular and emergency business.

People who have horses that have been exposed should know due to the quarantines (no horses in or out of a facility).

Horses who aren’t in the exposed population have a very low risk of contracting EHV-1. The risk is never zero, however. Trail rides, etc. for horses that haven’t been exposed carry a very low risk.

For those horses that were not at the Ogden show or that did not come into contact with horses at the Ogden show, there is no more risk of EHV-1 than there was before the outbreak.

If you suspect exposure, take your horse’s temperature rectally twice a day for 21 days from the time of exposure. If the temperature is over 102 degrees F, please contact a veterinarian immediately. A fever also generally precedes the development of clinical/neurological signs.

Update on Pilchuck Patient

The Pilchuck patient is doing pretty well. We were able to start the horse on antivirals early and he is responding, although he has a way to go. He will be released once he stops shedding the virus and the state’s veterinarian says he can go home.

Pilchuck Veterinary Hospital remains open for elective and emergency equine cases. (Due to Pilchuck’s protocols, the horse would have immediately gone into quarantine even without the EHV-1 warnings, given its presenting symptoms.) No other horses have been exposed at PVH.


During this outbreak and at all other times, we recommend good biosecurity.

Although we don’t know exactly how long the virus lives outside a host, EHV-1 can be killed pretty easily.

Basic recommendations include not sharing any equipment among horses without first cleaning and disinfecting (1:10 bleach). Most disinfectants do not work in the face of organic debris (dirt, manure, etc.), so the cleaning step is critical.

Focus especially on items that come into contact with horses’ noses and mouths, as the virus is shed via nasal secretions: water buckets, bits, etc.

Once this outbreak is over, there will be others in the future, whether two months or two years from now. Good biosecurity will help to prevent and/or mitigate the risk.

Inquiries or More Information

Charlotte Graeber, charlotte@charlotte-works.com

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