Early last year, a deer euthanized as part of a study at the Kerr Wildlife Management Area research facility in Texas tested positive for chronic wasting disease — the deer equivalent of the brain disorder called “mad cow” in cattle and “Creutzfeldt-Jakob disease” in humans.

It was an alarming find for state wildlife officials, who have spent the last three years struggling to contain a recurring outbreak of the disease. Wildlife biologists widely view the highly contagious illness as the single greatest threat to the long-term health of the country’s cervids, a family of animals that includes deer, elk, moose and caribou. CWD causes brain proteins called “prions” to misfold, leading to a prolonged death by neurodegeneration.

The disease is present in free-ranging cervids in at least 32 states, according to the U.S. Geological Survey.

A buck whitetail deer, Odocoileus virginianus, stands near Goose Island State Park in Texas.

It also might have been a false positive. Follow-up tests failed to confirm the deer’s infection.

But environmental samples taken through the summer showed diseased prions lurking in feed and water troughs. When wildlife officials live-tested every deer in the herd in October, they turned up another positive. On Nov. 20, they killed all of the roughly 90 deer in the herd, depopulating the Texas Parks and Wildlife Department’s only deer research facility.

The infection at the Kerr research facility capped off a record year of CWD spread in Texas by raising the same question that has confounded officials since the case count started climbing in 2021: How does the disease keep working its way into new sites, when infected deer aren’t the ones spreading it?

The research facility is double high-fenced to keep the penned deer away from the wild ones roaming the 6,400-acre Kerr Wildlife Management Area outside. The facility maintained a “closed herd” that did not accept new deer from outside its fences. Researchers working there followed biosecurity protocols that included disinfecting boots and tools and using dedicated on-site vehicles. No deer had yet tested positive for CWD in the county.

“Everybody has been asking, including myself and our staff, how CWD showed up in the deer research facility,” Texas Big Game Director Alan Cain told HuffPost. “And we don’t have a good answer. Everything is just speculation.”

The disease first appeared in free-ranging mule deer Texas in 2012, along the state’s western border with New Mexico. Cases slowly ticked up in the years that followed, mostly concentrated in the original area and the panhandle. In both of those regions, the disease likely spread from free-ranging deer in neighboring states.

But CWD cases have skyrocketed since 2021, when the disease popped up at two separate deer breeding operations, kicking off a statewide search for all the deer that those breeders had sold to others. It’s not clear how CWD entered either of their operations. And in the years since, seemingly spontaneous outbreaks have continued to occur at far-flung deer breeder sites across the state, without a clear explanation.

What’s become increasingly clear, as the Kerr facility cases highlight, is that infected deer themselves aren’t always the ones spreading it.

No one can say with certainty how the disease is moving. Diseased prions can persist in the environment for years. It’s possible that carrion-feeding birds like vultures can pick up diseased prions and vomit them into water troughs, or that people can unwittingly spread prions after passing through a contaminated area or moving an infected carcass. It’s also possible that the disease can just happen for no reason at all.

“Those prions can move into the environment in numerous different ways ― that’s one of the challenges with the disease,” University of Minnesota molecular biologist Pete Larsen said at a Texas Wildlife Commission hearing in November. “Some amount can occur spontaneously. What we don’t know for deer is how often that happens.”

CWD appeared at 12 new captive deer-breeding facilities last year, and for the first time in free-ranging deer in Bexar and Coleman counties, making it “by far the most new areas for CWD detections in a single year,” Cain said.

The concentration of the disease on deer breeding sites has cast new scrutiny on the lucrative corner of the Texas hunting industry that uses pen-raised deer to stock high-fenced game ranches. By controlling genetics and feed, breeders can raise bucks with antlers that dwarf those found on wild deer. Some deep-pocketed customers will pay tens of thousands of dollars to shoot one.

While it’s unclear how the disease first worked its way into Texas breeder sites, concentrating deer in pens facilitates the spread of any contagious disease. Moving deer from one site to another, as Texas deer breeders historically have done, also makes it easier for diseases like CWD to spread.

The disease has become an existential threat to Texas deer breeders, whose numbers have dropped by half since peaking at nearly 1,400 in 2014, the year before the first positive case hit a breeder pen. Wildlife officials generally slaughter all captive deer on facilities that test positive for CWD in order to contain the spread, then require the breeder to disinfect the property. A positive case typically destroys the business.

The state wildlife commission voted in November to require live testing before transferring captive deer to another facility.

But facing an outcry from deer breeders and at least seven state senators, the commission tabled several measures proposed by wildlife officials, including one that would have required captive-bred deer to retain their ear tags permanently. The commission will reconsider the proposals when it meets later this month.

As the commission weighs how to contain the spreading disease, the state faces the prospect of losing some of its authority to speedily euthanize infected captive herds.

Robert Williams, owner of RW Trophy Ranch in Terrell, has refused to let state wildlife officials kill the deer in his breeding pens, despite more than 100 positive tests. A Kaufman County judge has scheduled a jury trial for next month to decide the case.

Like with the Kerr facility, Williams has no idea how the disease got onto his ranch. He hadn’t received a deer from off site in five years by the time one of the deer he bred yielded a positive CWD test.

The Kerr facility case may offer an opportunity for wildlife officials to study the question. For now, however, the site’s future is unclear.

“The facility is going to stay there for now,” Cain said. “At this point, it will sit vacant until we’ve had time to contemplate the options and opportunities.”

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