10,000 deer in Texas tested for deadly disease

By Shannon TompkinsJanuary 16, 2016

Since September, Texas wildlife officials have collected more than 10,000 tissue samples from mostly white-tailed deer in a program aimed at determining if transmissible, invariably fatal chronic wasting disease has entered the state’s free-ranging whitetail herd. Photo: Picasa Photo: Picasa Since September, Texas wildlife officials have collected more than 10,000 tissue samples from mostly white-tailed deer in a program aimed at determining if transmissible, invariably fatal chronic wasting disease has entered the state’s free-ranging whitetail herd.
Texas wildlife officials say all tests so far completed on tissue samples collected since September from almost 10,000 free-ranging white-tailed deer have proven negative for chronic wasting disease (CWD), a transmissible, invariably fatal neurological illness not documented in the state’s whitetails until last summer when captive whitetails in Medina and Lavaca counties tested positive for the malady.
“So far, so good. There have been no reported positives,” Mitch Lockwood, director of big-game programs for Texas Parks and Wildlife Department, said of results of completed laboratory tests of brain tissue collected by agency staff.

The testing is part of the enhanced CWD surveillance program initiated in the wake of the discovery of the disease in five whitetails held in two of the state’s 1,300 or so captive deer breeding/rearing operations.

CWD, now found in 23 states and two Canadian provinces, affects only a handful of cervid species, including whitetail, mule deer, elk and moose. First documented in Colorado in 1967 in captive mule deer, CWD is a progressive disease that evidence indicates is caused by a infectious prion (a protein-based agent) that triggers lesions in brain tissue. As the disease, which can take as much as two years or more to manifest, progresses, it affects the animal’s neurologic and physiologic functions, resulting in abnormal behavior, deterioration of physical condition (wasting) and, eventually, death.


Like other prion-related, brain-degenerating diseases such as “mad cow” in bovines, scrapie in sheep and Creutzfeldt-Jakob disease in humans, the disease is incurable. The origin of CWD is unclear, although there is no evidence it is endemic in North America’s cervids; a commonly espoused theory is that it likely originated as a mutation of another prion-related disease that “jumped” species.

The prion associated with CWD appears transmissible between deer through bodily fluids or through prions shed by infected animals. Those prions can persist for years in soil, and recent evidence indicates they can be absorbed by plants.

While CWD is highly infectious among deer, there is no evidence that it is transmissible to humans, even those who eat meat from infected animals. But the World Health Organization and the U.S. Centers for Disease Control and Prevention recommend, as a precaution, not consuming meat from CWD-infected animals.

Texas has had an aggressive CWD surveillance program focused on the state’s free-ranging whitetail and mule-deer herds since 2002. Before the 2015-16 monitoring program ramped up in September, agency staff had collected brain tissue samples from more than 30,000 free-ranging deer. While the program has found a handful of CWD-positive mule deer in an isolated herd in the Hueco Mountains of far West Texas, all free-ranging whitetails have tested negative.

Because the only CWD test deemed 100 percent reliable requires tissue samples taken from an animal’s brain, only dead deer are involved in the surveillance program. Almost 2,000 of the more than 10,000 samples so far collected in the 2015-16 program have come from road-killed animals. Most – more than 8,100, as of last week – were taken from deer harvested by Texas hunters who voluntarily agreed to allow TPWD staff to remove a small amount of brain tissue from their deer.

TPWD staff approached hunters at locker plants and deer processors, made arrangements with cooperative hunters and landowners on private lands and solicited samples from successful hunters on public hunts on agency wildlife management areas and state parks.

“Getting hunters to help us by volunteering to have their animal included in the sampling has been crucial to the program,” Lockwood said. “We had a great deal of cooperation. There’s been some reluctance here and there, but, overall, hunters and landowners have been highly cooperative. We’re really proud of that. This was a huge undertaking.”

And an expensive one. Lab fees for CWD tests on the brain tissue are $30 apiece – $300,000 for 10,000 samples. Also, TPWD hired six “seasonal” employees to staff deer-check stations and otherwise assist in the CWD surveillance work. Funding of those costs comes from a combination of revenues generated through sale of “Hunt Texas” vehicle license plates that feature a white-tailed buck and Pittman-Robertson Fund monies, and reimbursement of federal excise tax paid on firearms, ammunition and other hunting-related equipment.

Sampling covers state

TPWD designed the 2015-16 CWD surveillance effort with the goal of strategically sampling the state’s 4 million free-ranging whitetails in a way that would, using scientifically accepted statistical analysis, yield a 95 percent confidence level that the program would detect CWD if as few as 1 percent of deer were infected.

To do that, the agency set sampling goals for each of the state’s 33 Resource Management Units. The RMUs’ boundaries are designed to arrange the state’s deer herds into fairly distinct populations based on habitat, land use and terrain.

The sampling goal for each RMU was based on the unit’s deer population, density and distribution, as well as risk factors such as history of importing CWD-susceptible animals or proximity to a site where a CWD-positive deer was documented.

The program had a statewide goal of collecting about 7,600 tissue samples. As of this past week, agency staff had collected 10,006 samples, including 9,500 from whitetails, 456 from mule deer, 12 from elk and 38 from “exotic” deer such as axis, fallow and red stag.

“We’ve far exceeded the goal as far as the number of samples,” Lockwood said. “But we’re still looking to hit the goals for some individual RMUs, especially some of those in the Panhandle and other places where the deer density is low or there’s not much hunting pressure.”

Still time to meet goals

As of this past week, all but 13 or the 33 RMUs had meet or exceeded their sampling goals, some collecting as many as 350 percent of the target. And several of those 13 units were at 80-90 percent of more of their goal.

One of the areas where the sampling goal hasn’t been met is a specially drawn unit covering a five-mile radius around the Medina County captive-deer facility where the first CWD-positive whitetail was discovered. The agency set a goal of sampling 300 free-ranging whitetails from that area. As of last week, 73 samples – 24 percent of the goal – had been collected.

“We’ve still got some time left, and staff is working extremely hard to hit those goals,” Lockwood said.

TPWD staff is not the only group working hard on the CWD surveillance project. The Texas A&M Veterinary Diagnostic Laboratory, which is handling testing of samples, has been swamped with the thousands of submissions.

That flood of samples has resulted in a considerable backlog. Complete testing of all 10,000-plus samples is likely to take several more weeks, Lockwood said.

“It’ll be awhile before we get the results from all of the samples,” he said. “But I’m confident that if (CWD) is out there right now, even at an very low prevalence, we’ll know it.”