Oregon horses

Oregon officials have reported two serious viruses infecting horses.

At least six horses in four counties scattered across southern and eastern Oregon have tested positive for West Nile virus in recent weeks, according to state agriculture officials.

None of the infected horses — two in Klamath County, two in Malheur County, one in Umatilla County and one in Baker County — had been recently vaccinated against the virus, said Ryan Scholz, state veterinarian for the Oregon Department of Agriculture.

Three of the horses were euthanized, while the other three are recovering, Scholz said. One additional suspected case in northeast Oregon is still under investigation.

“We’re seeing a lot of West Nile virus right now,” Scholz said. “It’s always unvaccinated horses that get infected.”

Wild birds are the primary hosts for West Nile virus, though it can be transmitted to both humans and horses by mosquitoes. The effects of the disease in horses can range from mild flu-like symptoms to inflammation of the brain, which is fatal in approximately one-third of all cases.

ODA encourages horse owners to vaccinate their animals to prevent further infections.

“It is an easily preventable disease,” Scholz said.

Three horses on a farm in Linn County were also diagnosed with a different contagious disease called Equine Herpesvirus Myeloencephalopathy, caused by the virus EHV-1.

The farm, which was placed under quarantine, had five horses exposed to EHV-1, Scholz said. Three of the horses tested positive on Sept. 9, and two were later euthanized. One is recovering, and the other two were not infected.

EHV-1 is highly transmissible between animals. However, Scholz said a preliminary investigation shows none of the five horses were moved off the farm or in contact with other horses within the past four weeks.

“We just want to reassure people that we do not know of any exposure risk at this point,” Scholz said.

Herpesviruses are common in horses, Scholz said. Normally, EHV-1 results in a mild respiratory disease, though it can mutate to develop potentially serious neurological symptoms, such as a lack of coordination, hind limb weakness, inability to urinate and inability to rise, among others.

Scholz said it appears this mutation happened in one horse at the farm in Linn County before spreading to the other two. No other animals appear to be at risk.

{p class=”p1”}”They haven’t been going to shows, they haven’t been going to other barns,” Scholz said. “In this case, I think we got really lucky.”

Perhaps the most well-known instance of EHV-1 in Oregon, Scholz said, was in 2015 when just before the state high school team equestrian championship in Redmond nine horses fell ill and the event had to be rescheduled. No horses died in that event.

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