Four Willamette Valley horses have tested positive for contagious equine herpes virus, and veterinarians warn horse owners to watch for neurologic symptoms in their animals.

Two of the horses were treated at Oregon State University’s veterinary hospital. Horses at Marion County and Polk County stables and another farm have been quarantined.

The first horse to fall ill showed signs April 28 and a diagnosis of EHV-1 was confirmed the following day. Horses from the Marion County stable were at events at the Linn County Fairgrounds in Albany April 16-19 and at the Oregon Horse Center in Eugene April 25-26.

Owners who also had horses at the events or have questions about the virus should contact their vet, said Dr. Ryan Scholz, the Oregon Department of Agriculture’s western district veterinarian. He said there was no immediate sign of neurologic problems among the horses quarantined at the stable.

EHV-1 is one of the most common respiratory viruses among horses; by age 2 most horses have been exposed to it, Scholz said. It’s a lifelong infection, but lies dormant most of the horse’s life. But every once in a while, triggered by stress or other factors, it pops up and attacks the nervous system, he said.

The virus in this case is a common form, Scholz said. It is not the mutated form of the virus that caused an outbreak among horses at a national cutting horse competition several years ago, he said.

The virus can’t be transmitted to people but spreads among horses through animal-to-animal contact or contaminated equipment, clothing or hands.

Symptoms include fever, decreased coordination, nasal discharge, dribbled urine, loss of tail tone, hind limb weakness and poor balance, according to an ODA news release. Sick horses may be unable to rise.

The virus can cause pregnant mares to abort. Severe cases can kill horses. Vaccinations are available, but Scholz said they are short-lived and must be combined with good bio-security management practices. The department does not recommend for or against the vaccine, but encourages horse owners to discuss it with their veterinarian, he said.

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