Four horses test positive for EHV-1 in Wyoming |

Four horses test positive for EHV-1 in Wyoming

Three horses that were recently associated with barrel races in Wyoming have tested positive for the "wild" strain of EHV-1, or EHM. A fourth is showing symptoms. Getty Images photo.
Getty Images/iStockphoto | iStockphoto

Four horses in Wyoming have tested positive for the neurologic type (EHM) of equine herpes virus, or EHV-1.

All four horses have been associated with barrel racing events in recent weeks, at least two of them at the Cam-Plex in Gillette, Wyoming in recent weeks. Neither of those horses was stabled at the Cam-Plex, however.

According to the Associated Press, the Cam-Plex in Gillette, Wyoming, is being sanitized in response to the disease. Staff cleaned the East Pavilion and Barn No. 3 as a precaution and at the recommendation of the Wyoming Livestock Board and a local veterinarian.

The first horse that tested positive has been euthanized, but the other three are still being treated.

The most recent case was admitted to a veterinary facility on Feb. 6 and a positive test result was returned on Feb. 7.

As of Feb. 9, three premises, two private and a boarding facility, were under quarantine, affecting 26 horses. Quarantined premises are checking exposed horses’ temperatures twice a day and implementing biosecurity measures.

The Central States Fair reported on its Facebook page that the James Kjerstad Event Center in Rapid City, S.D. will be closed for horse events until Feb. 14 as a precaution—no disease-related issues have been reported there.

For the most current information about equine outbreaks nationwide, and more information about equine disease, visit

What is EHV-1?

EHV-1 manifests with respiratory symptoms, such as a cough and nasal discharge, or neurologic symptoms, such as lack of coordination, inability to stand, urine dribbling and loss of tail tone. EHV-1 may also cause abortion in brood mares.

Respiratory disease due to EHV-1, sometimes referred to as rhinopneumonitis, is most common in young horses that have been under stress, as that caused by weaning. Horses often recover, although there isn’t a specific treatment other than supportive care.

The neurologic disease can be caused by either a mutation of the wild-type EHV-1 virus, or by the neuropathic EHV-1 virus. The neurologic symptoms resulting from the mutation of the wild-type EHV-1 virus are called equine herpesvirus myeloencephalopathy, or EHM. The neuropathogenic strain of EHV-1 is much less common and more aggressive, with a higher mortality rate.

The symptoms of EHM can be treated, but sometimes euthanasia becomes the most humane outcome, South Dakota state veterinarian Dustin Oedekoven said.

How is it spread?

“The wild-type EHV-1 virus is very common among the horse population, but often doesn’t cause symptoms until the horse has been under the stress of transportation, competition or just being around other horses,” Oedekoven said. The stress suppresses the immune system, allowing the virus to cause disease.

EHV-1 is spread by direct or indirect contact with nasal secretions, so any tack, equipment, facility or person who has come into contact with an infected horse can pass the virus on.

Some horses that have the virus may spread it before exhibiting any symptoms, and some horses can pass the virus on without ever exhibiting symptoms, Oedekoven said. According to a document provided by APHIS, most horses have been exposed to the virus by the time they are 2 years old, and foals are often infected by their dams.

How is it treated?

“The earlier EHV-1 is caught, the better the chance for recovery,” Oedekoven said. Whether the horse is showing neurologic or respiratory symptoms, the only treatment is for the symptoms themselves. The owner may not know the horse has EHV-1 with respiratory symptoms because the symptoms go away on their own and never warrant testing.

Horses with neurologic symptoms receive anti-inflammatory medication to reduce the swelling of the brain and spinal cord. Pressure sores can become an issue on horses that are unable to stand. “The recovery process can be long and the success may depend on the amount of time, effort and care the owner and veterinarian can provide,” Oedekoven said.

How can you prevent it?

A vaccine is available that helps prevent the respiratory symptoms and abortion, as well as reducing the likelihood of passing the virus on, but is ineffective against the neurologic symptoms and the neuropathogenic strain of EHV-1.

“One other problem with the vaccine is that it has a fairly small window of effectiveness,” Oedekoven said. “It should be used about three weeks before you anticipate your horse being stressed or exposed to other horses, and boostered every 90 days while there is a chance of exposure. Brood mares are commonly vaccinated at five, seven and nine months of gestation.”

Oedekoven recommends never sharing buckets, brushes or tack, and regularly cleaning and disinfecting trailers and anything else that may serve to harbor the virus.

Oedekoven also recommends isolating horses that have been co-mingled with other horses for 28 days before allowing them to be around horses that remained at home. “Otherwise you may be exposing the horses back home to the same diseases that the horse that traveled was exposed to,” he said.

Oedekoven encourages horse owners and event organizers to be aware of what’s going on in the industry and take biosecurity precautions to prevent the spread of not just EHV-1, but other contagious diseases as well.

It’s up to the event organizers as to the extent of precautions they want to take, Oedekoven said. Some events have been cancelled, others are implementing more stringent health requirements. “One thing they can do is strictly adhere to the state requirement to have a current health certificate,” Oedekoven said. “The health certificates themselves may not be a guarantee of health, but it means the owner has to be in contact with a veterinarian who will be aware of current health issues.” A health certificate is valid for 30 days, but if the owner notices any signs of illness they should contact their veterinarian promptly and voluntarily quarantine their horse until they can obtain a clean bill of health. Health certificates are required at all public exhibitions of livestock, including horses, in South Dakota.

Requiring a temperature reading for each horse at the event every day is another way to minimize the chance of spreading the disease, since fever is one of the early indications of EHV-1.

Oedekoven said all horse owners, whether they are traveling or not, should be aware of the situation and talk to their veterinarian about appropriate vaccinations and prevention practices for their horses. Even horses at brandings and community events have the potential to be exposed to the virus.

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