Equine virus outbreak has horse owners on alert

Scott Swanson

An outbreak of equine herpes virus-1 in several western states, including Oregon, has put the brakes on local equestrian activities and may be a threat to the horse-related activities at the County Fair.

As of late last week, cases of the disease, which affects horses, llamas and alpacas, had been diagnosed in three Oregon counties – Union, Deschutes and Clackamas – prompting officials to hold an informational meeting on the topic at the College of Veterinary Medicine at Oregon State University and to cancel equestrian events at Linn County Fair and Expo Center through at least June 5.

Equine herpes virus-1, or EHV-1, can cause neurological damage, respiratory problems, abortion and neonatal death in horses and camelids.

Robin Galloway, OSU Extension Linn County 4-H agent based at the fairgrounds, said that the closures are a precaution and that they could be extended.

“The challenge is that people can carry the disease on their clothing and can pass it on to horses even if they don’t have horses,” she said. “These are just security measures to try to minimize exposure.”

Though many animals may carry the virus, it generally remains inactive until triggered by stress, including excessive exercise, during long-distance transport, or at weaning.

EHV-1 is the primary cause of equine herpesvirus myeloencephalopathy, which is considered an “emerging disease” that causes damage to the blood vessels in the brain and spine and can be fatal. Outbreaks have occurred at large horse facilities and events – including race tracks, horse show grounds, and boarding stables.

Signs of EHV-1 include fever, decreased coordination, incontinence, loss of tail tone, hind limb weakness, leaning against walls or fences to maintain balance, lethargy and inability to rise.

In this latest outbreak, EVH-1 has been diagnosed in California, Washington, Idaho, Colorado and Utah, as well as Oregon.

OSU veterinary officials say EHV-1 is spread primarily from horse-to-horse contact, but can also be transferred via indirect contact, especially from infected tissues from fetuses and fetal membranes.

The current outbreak has been traced back to the National Cutting Horse Association’s Western National Championships held in Ogden, Utah, on May 8, where a number of horses in Oregon were present. According to the Deseret News in Salt Lake City, as of Monday, May 30, positive cases had been confirmed in 13 California counties as well. Most of the affected horses were in Utah, but two apparently were exposed to the disease at the Kern County Cutting Event in Bakersfield, Calif., on May 13.

Galloway said the current strain of the virus seems to be resistant to existing vaccinations.

“It seems to be fatal unless the symptoms are mild enough or they catch it early enough to treat it,” she said.

Angela Burger of Holley, leader of the Rhinestone Riders 4-H equestrian group for 12 girls from the Sweet Home and Brownsville areas, said that her group has cancelled all events during the month of May.

She said that the group does plan to ride in Lebanon’s Strawberry Festival Parade.

“All of our horses are privately facilitated and the chance of coming into contact with the disease is none,” she said. “We’re going to do the parade and make sure the girls know they shouldn’t touch other horses. We want the girls to be cautious but not intimidated by it.”

Burger said she’s had previous experience with similar outbreaks. During the West Nile Virus epidemic a decade ago, one of her own horses got the virus from a vaccination, she said.

“We don’t try to hard too stop these things,” she said.

Galloway said the fact that the weather has been rainy for much of the spring has made it difficult to have to cancel events inside the fair’s covered horse arena.

“The immediate challenge is kids really want to keep their horses worked prior to the county fair,” she said.

There are no real set guidelines on what to do or not to do to avoid the virus, Galloway said.

“What we’re advising folks right now is to use their own common sense, determine what their own level of comfort is,” she said. “We’re not sure what’s going to happen with the fair. Usually what the state Department of Agriculture and the state veterinarian recommend, that’s how we decide what we are going to do.”