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EHV-1 in King County: What You Need to Know

On December 15th we received an alert from the Equine Disease Communication Center (EDCC) regarding a horse that tested positive for Equine Herpesvirus type-1 neurotropic strain at a barn in King County, WA. To start, we would like to express our sincerest condolences to all those who have lost a horse during this outbreak, and we are sending healing thoughts to those whose horses are currently battling the disease.

In the last several days more information has been released about this outbreak, and we have been contacted by numerous concerned horse owners. Following is a quick summary provided by Red Rock Equine Veterinary as of December 26th, including details from the WA State Dept. of Agriculture and WA State Vet Medical Association. Keep an eye on our Facebook page for updates as we'll be closely monitoring this outbreak.

King County Equine Herpesvirus (EHV type-1)

  1. Only one facility has been affected by the Equine herpes virus outbreak - Gold Creek Equestrian Center in Woodinville, WA. * Frequent updates are posted on their Facebook page


  3. There are 60 horses at the facility out of which test results have been finalized on 37 of them. 9 horses have been confirmed to have tested positive for the neurotropic strain, 7 of which have been euthanized. The two other horses are still sick and but are improving. A third horse has had elevated temperatures but has not developed neurological symptoms. (Updated 12/27/17)

  4. The facility is under state quarantine, meaning that no horses may come onto or leave the property. Above-standard biosecurity protocols have been enforced and are being followed.

  5. There is a dedicated local equine veterinarian exclusively working with the facility and horses on a daily basis. The dedicated veterinarian is not in contact with/attending any other patients/horses as a precaution.

  6. The WA State veterinarian, among other authorities, are involved and assisting in the situation.

  7. There are several types of Equine Herpesviruses (1, 2, 4, 5). The one involved here is the type-1. Among the type-1s there are different strains. Some strains only cause fever and respiratory symptoms while others can lead to neurological symptoms, and a small group of the neurological cases are caused by a more virulent (aggressive) and newer strain (neurotropic strain).

  8. If a horse is infected by the Equine herpesvirus and develops the neurological form, the condition is then called Equine Herpes Virus Myeloencephalopathy (EHM).

  9. Most healthy horses carry one or more strains of the type-1 equine herpesvirus. It’s the same group of herpesvirus as the one that causes cold sores in people. Once you have it you carry it for many years or life. However, it will only clinically manifest when stresses or immunosuppression is in place. When it is clinically present the individual is highly contagious to others, even the ones that have the dormant herpesvirus.

  10. The Rhino vaccine most horses receive routinely (twice yearly) is the vaccine for some of these herpesviruses, including the type-1. Unfortunately, it does not provide protective immunity against the EHV-1 neurologic/neurotropic strain. However, there is still research trying to understand if the vaccine may help with the severity of these cases and spread of the virus.


Details from the WSVMA and WA State Department Of Agriculture

  • On December 16th 2017, the Department of Agriculture was notified of one laboratory-verified case of Equine Herpes Virus Myeloencephalopathy or EHV–1, neuropathogenic strain, in King County, WA. Quarantine was immediately instituted by the Department of Agriculture and the Department is working closely with the facility and their veterinarian to contain this outbreak. Subsequent testing identified an additional five infected horses at the facility.

  • As of 12/26/2017, 7 horses with neurological signs had been euthanized out of the population of 60 horses.

  • EHV–1, neurotropic form, is a highly contagious virus that can result in fatal illness in horses. The disease is spread from horse to horse through direct contact, on feed, tack and equipment. While people cannot be infected by the virus, they can carry the virus on their clothes or hands. Horse owners should carefully wash their hands, clothing and equipment and avoid using the same equipment on different horses.

  • In addition to the quarantine, additional testing of horses that have been housed near the affected horse or horses demonstrating clinical signs has been conducted. Tracing of animals that may have come into contact with the infected horse is ongoing.

Given the highly infectious nature of the virus, here are some strong recommendations for horse owners.

Closely observe your horse and look for signs of possible infection, which include:

  • Fever of 102 degrees F or higher

  • Discharge from the eyes or nose

  • Respiratory symptoms

  • Swelling of the limbs

  • Spontaneous abortions

  • Neurological signs such as unsteady gait, weakness, urine dripping, lack of tail tone and recumbency.

Be sure to obtain and record the body temperatures of all horses on the premises twice daily, ideally first thing in the morning and last thing at night, and before administering medications as some medications can lower body temperature.

Most importantly, if you detect any of the symptoms above, notify your veterinarian immediately. Your veterinarian may want to take nasal swabs for virus detection or blood samples for evidence of exposure to EHV–1.

To protect your horse from becoming infected and help limit the potential spread of this virus, here are several things all horse owners should be doing.

  1. Monitor all horses on your premises for the previously described symptoms.

  2. Limit direct horse-to-horse contact.

  3. Limit stress to horses.

  4. Don’t share equipment between horses.

  5. Clean barn areas, stables, trailers or other equine contact surfaces thoroughly, removing all organic matter (dirt, nasal secretions, uneaten feed, manure, etc.) before applying a disinfectant. Organic material decreases the effectiveness of disinfectants. Mix disinfectants according to the manufacturer’s recommendation and follow their recommendations for contact time.

  6. Use footwear disinfectant and hand sanitizer when moving between areas.

  7. If you have a potentially exposed horse, restrict human, pet and vehicle traffic from the area where the exposed horse is stabled.

  8. Clean all shared equipment and shared areas, again removing dirt and manure before application of a disinfectant.

  9. Self-quarantine any horses with possible symptoms away from other horses and contact your veterinarian immediately.

The time between exposure and illness from EHV-1 can vary from 2 to 14 days. By self-quarantining animals with possible symptoms, practicing good biosecurity on the farm, and during travel, and contacting your veterinarian as soon as you suspect possible symptoms, horse owners can do a lot to prevent further spread of the virus.

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