Las Vegas Sun

March 28, 2024

Las Vegas dodges bullet in equine herpes outbreak

Horses in Southern Nevada have escaped a deadly equine herpes virus that caused the South Point Arena & Equestrian Center to postpone a major event and require that all horses brought to the facility be tested for fever.

The virus, traced to a cutting horse competition in early May in Ogden, Utah, spread to 10 states. It attacked the nervous systems of two horses in Washoe County and caused mild fever in a third in Elko County, but all are expected to survive.

Anette Rink, supervisor of the Nevada Agriculture Department’s animal disease laboratory in Sparks, said that the worst of the threat in Nevada is over, although future outbreaks are always possible.

“We have already sounded the all-clear,” Rink said. As a precaution, South Point Arena General Manager Steve Stallworth postponed a National Barrel Horse Association event from June 2-5 to July 7-10. Stallworth said the horse owners for the event, which brings in about 1,200 horses, were grateful for the postponement because they, too, want to guard against spreading the virus.

“The horse industry is so passionate, so conscientious,” Stallworth said. “We actually caught a major break, because we didn’t have any scheduled horse events from April 30 until this month.”

Beside the postponed event, South Point began requiring owners of other horses brought to the arena to stipulate in writing that their animals weren’t at the Ogden competition. The owners also have to take their horses’ temperatures twice daily to make sure they don’t have a fever.

Stallworth said the testing will probably continue through next week, when Peruvian horses appear at the arena. So far, though, no horses at South Point have been detected with a fever or virus, including the polo horses that were available for a media event Tuesday, the Budweiser Clydesdales that will appear today and the jousting competition horses that will be on hand Saturday.

But the virus has been deadly.

In Fort Lupton, Colo., the death of Chief, a highly trained performance horse found last month in his stall, unable to stand, the victim of the raging neurological infection, was certainly a major emotional and financial loss for his owners.

But his death was also a signal event for animal epidemiologists, almost certainly the first confirmed fatality in a highly unusual outbreak of an equine herpes virus. Since the horse competition in Utah, at least 88 animals have been infected, including 12 that were euthanized when the virus attacked their nervous systems, as it did Chief’s.

The equine herpes virus, or EHV-1, is well-known, a scourge believed to have existed at least since the 1700s, although some researchers contend a newer variant may be causing the more serious neurological illnesses seen in recent years. The virus, which infects only horses, can be spread through the air or contaminated equipment, clothing and hands. Notable outbreaks occurred in Ohio in 2003 and in Colorado in 2007.

But this one has been different, and the pattern of exposure has prompted an investigation sprawling across 21 states and Canadian provinces. Fearing that the epidemic could rage for months, killing hundreds of expensive and highly trained horses, the competition cutting horse industry — with $40 million in annual prize money, 50,000 breeding and performance horses, and more than 2,200 annual shows — was shut down.

“What was remarkable here is the dispersal,” said Dr. Paul Morley, a professor of biosecurity and epidemiology at the Colorado State University Veterinary Teaching Hospital in Fort Collins, where the necropsy on Chief was performed. Morley called that pattern, at least for animal viruses, probably unprecedented.

More than 400 horses congregated together for 10 days in the sweaty, nose-nuzzling competition in Ogden. Then they headed back home to scores of ranches and training facilities where they congregated with horses that had not been to Utah.

“The animals were already gone before anybody knew there was a problem,” said L.M. Granger, the director of the centers for epidemiology and animal health at the federal Agriculture Department.

The virus incubates for up to 10 days, so by the time the first confirmed cases appeared — Chief on May 12, a handful more over the next few days around the country — thousands of horses each valued at $100,000 or more were endangered from California to Illinois and most states between.

That the virus killed quickly added further urgency to the outbreak. Horses went from healthy to critically ill literally overnight.

“We got home Monday night, and everybody seemed great,” said Becca Francis, a trainer at Kenny Platt Cutting Horses, where Chief lived. Even as late as Tuesday night, at a last check on the 50 or so animals that train and board there, there were no signs of trouble.

Just eight hours later, on Wednesday morning, May 11, Chief was down, the virus having attacked the blood vessels in his spine. “He was lying perfectly quiet in the center of his stall, but he couldn’t get up,” Francis said.

In most previous outbreaks, the official response would have been to quarantine the Platt place and let the virus burn itself out, treating horses as they got sick with antiviral drugs like valacyclovir, also used to treat herpes infections in humans.

But as other cases began popping up, investigators realized the virus had dispersed in every direction. Of the 88 animals confirmed with infections this month, 58 had been at the Ogden show, according to the Agriculture Department. The other 26 cases were in horses exposed to stablemates that had been at the show. Morley called the situation “a perfect storm.”

Coordination across state agriculture offices was put into place to monitor cases. On May 13, the day after Chief’s necropsy, Keith Roehr, the Colorado state veterinarian, sent an email to his counterparts in every state and Canadian province where the horses had come from. The Ogden competition was suspected, he said in the email, as “a place of interest.” By the end of that weekend, new cases had been confirmed in California, Nevada and Utah in horses that had been to Ogden.

No one knows where the original infected animal came from, and veterinarians say it will probably never be determined, since some horses get such mild cases that a residual antibody in their blood is the only evidence they had the virus at all.

The outbreak seems to be waning. The Agriculture Department listed no new cases last week, and Utah officials said that horse owners there should feel free once again to participate with their animals in horse events like rodeos or parades.

The New York Times contributed to this report.

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