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Wednesday, February 7, 2024
Kim Vaughn

Equine Herpes Virus outbreak reported in Spokane County

2/21/24 UPDATE on the Equine Herpes Virus (EHV) outbreak in Spokane County.

There are 2 quarantines associated with 1 farm.

  • Multiple horses have experienced either the respiratory, abortion, and neurologic forms of the disease (EHM). 
  • The last EHM case reported on the quarantined premises was on 2/15/24.
  • There is NO evidence the disease has spread to other facilities. 
  • There is NO history of these horses recently attending a show or event.
  • The owner has been extremely cooperative and has employed STRICT biosecurity that is being overseen by WSDA field veterinarians. 
  • The quarantines will be lifted 21 days after the LAST clinical signs of EHV. 

WSDA has NOT mandated that shows and events be canceled or postponed in Spokane County, but event coordinators may be making decisions based on THEIR biosecurity protocols or perceived risk. 

The virus incubation period is highly variable and can be as long as 14 days. Taking temperatures routinely can help with early detection. 
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Equine Herpes Virus (EHV) is a common, highly contagious equine viral disease causing four forms of infection that cause respiratory, neonatal, abortion, or neurologic signs. The neurologic form, or Equine Herpesvirus Myeloencepahlopathy, (EHM) is often fatal.  

This neurological disease presents itself as a result of damage to blood vessels in the brain and spinal cord associated with herpes infection. Interference with the blood supply leads to tissue damage and a subsequent loss in normal function of areas in the brain and spinal cord.

If the horse has neurologic signs and a positive test, we consider it as a case of EHM. EHM not only has the potential to affect horse health but, requires lengthy quarantines or cancellations of events like rodeos and fairs, the economic consequences can be equally devastating.

As we enter the time of year when horses are more active and travel to public events, it's especially important to observe appropriate biosecurity measures, vaccinate for EHV as it may be cross-protective for EHM, and watch for early signs of the disease.

A case in Washington


This week, a horse in Spokane County tested positive for Equine Herpes Virus 1, neuropathogenic strain (EHM). Two other horses have died with neurologic signs, and 3 out of 33 others have clinical signs consistent with various forms of EHV (neuro/down, abortion, pleuropneumonia). A quarantine has been placed on the facilities with exposed horses.  

This outbreak should serve as a timely reminder to apply appropriate biosecurity measures, update vaccinations, and be vigilant for signs of the disease. Usually, low-grade fever will proceed other clinical signs, emphasizing the importance of routine temperature monitoring for early detection. Check your horse’s temperature twice daily, ideally first thing in the morning and last thing at night. Also, check before administering medications since some can lower body temperature.

What to watch for 


Given the infectious nature of EHV-1, WSDA asks horse owners to follow these recommendations.

Watch your horse for signs of possible infection including:
  • Fever of 101.5 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.

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

When the virus is detected, WSDA and local veterinarians work closely with affected communities to ensure the best biosecurity standards are practiced.

The time between exposure and illness from EHV-1 varies from two to 10 days. By self-quarantining animals with possible symptoms, practicing good biosecurity, and contacting your veterinarian as soon as you suspect possible symptoms, you can help prevent the spread of this virus.

For more information, contact WSDA's Animal Health Program.

equinediseasecc.org/alerts