Chronic Wasting Disease: Coming to a Deer Population Near You

Without more federal dollars, the fatal disease will spread unabated

By Andy McGlashen

March 11, 2018


Photo by zorandimzr/iStock 

In 1967, at a research facility in Fort Collins, Colorado, scientists began to notice strange symptoms in a herd of captive mule deer. The deer guzzled water, ground their teeth, and drooled. They stopped eating and stared at nothing. Eventually—ribs protruding, heads drooping—they died.

By the time researchers formally described the condition and named it chronic wasting disease, or CWD, in a 1980 paper, it had spread to other facilities in Colorado and Wyoming. Since then, the disease has turned up in captive and free-ranging deer, elk, and moose in 25 states—Mississippi reported its first CWD-positive deer in February—as well as Canada, Norway, and South Korea.

No one knows when or how CWD arose. It belongs to a family of diseases called transmissible spongiform encephalopathies, or TSEs, along with mad cow disease, the sheep disease scrapie, and Creutzfeldt-Jakob disease, a very rare illness in humans. They are caused by prions, a type of protein that can become misshapen and cause other proteins to deform, eventually carving tiny holes in the brain. Like other TSEs, CWD is always fatal.

Unlike those diseases, however, CWD is not contained to domestic herds—it is the first known prion disease loose on the landscape, and wildlife managers are scrambling to stop it. Eradicating the disease seems unlikely. Stopping its spread may be the best we can hope for, experts say, and unless it’s backed by major new funding from Washington, hoping won’t get us far.

“Right now, we do not have effective management tools for this disease,” said Bryan Richards, emerging disease coordinator for the U.S. Geological Survey National Wildlife Health Center. “From a management standpoint, its characteristics form a terrific challenge for wildlife managers. There’s nothing easy about it.”

There are no documented cases of humans contracting CWD, but experts say they can’t rule out the possibility. Indeed, scientists believe exposure to beef infected with mad cow disease is the cause of a Creutzfeldt-Jakob variant that has infected at least 231 people worldwide since it was first recorded in 1996. Concerns grew last May when Stefanie Czub, a prion expert with the Canadian Food Inspection Agency, presented worrisome findings from her lab: As part of an ongoing study, three macaque monkeys that were fed CWD-tainted venison contracted the disease, demonstrating that it can cross the species barrier to primates. “The take-home message here is I think very much reiterating what the World Health Organization says: Nobody should consume any tissue, organ, or material from a prion-infected animal,” Czub said.

It’s difficult to say how many people eat venison, but 9.2 million Americans hunt deer, elk, and other big game. Montana hunters alone harvest more than 9 million pounds of deer, elk, and antelope a year. Hunting is economically important in many areas and is a key tool for managing North American deer herds. If concerns about CWD erode participation, hunters and nonhunters alike may see lost revenue, more crop damage, and more frequent car-deer collisions, natural resource managers warn.   

Shed in the waste of infected animals, prions can linger in soil for years. Research suggests plants can take up the prions and infect grazing deer. Females pass it to their offspring. Scavengers scatter prions across the landscape after visiting infected carcasses. CWD also travels when hunters transport contaminated parts, and when animals are shipped from captive facilities where they’re raised for venison or as stock for private hunting preserves.

In some areas the disease has become so well established that “if you’re a deer hunter and you go kill a big buck, you can take a coin out of your pocket and flip it up in the air, and those are literally the chances of that animal having CWD,” Richards said. In those hot spots, the disease is a threat not only to individual deer but also to entire local populations. In a 2016 University of Wyoming study of whitetail deer in the eastern part of that state, researchers found a 10 percent annual population decline from CWD, enough to wipe out some herds in less than 50 years.

To control the disease, 32 states have implemented bans or restrictions on importing captive animals from areas with CWD, and 42 ban or restrict hunters from bringing in animal parts from other states, according to the Chronic Wasting Disease Alliance, a partnership of conservation groups. States also track the disease in wild herds by encouraging or requiring hunters to bring deer and elk to checkpoints for testing, and occasionally by sending in sharpshooters to kill deer in areas with CWD.

Those state surveillance efforts are expensive—Wisconsin spent more than 32 million to manage CWD from 2001 to 2006—but federal support for them has withered even as the disease has spread across the country. In the mid-2000s, Congress gave the USDA more than $18 million a year to help states control the spread of CWD, with the money split between surveillance of captive and wild herds. But beginning in 2012, the wildlife dollars were eliminated, leaving states to pay for hunter check stations, lab fees, and other costs. Today that funding is down to $3 million a year for a USDA certification program for captive herds, which requires five years of CWD-free test results before a farm can move animals across state lines. Even so, some certified herds have later tested positive for the disease.

“We need a large amount of money to look at new management techniques,” said Matt Dunfee, director of special programs for the Wildlife Management Institute and head of the Chronic Wasting Disease Alliance. “Because research has been gutted nationally for this, it’s really hard to develop new tools.”

More money could be on the way soon. In November, U.S. Representatives Ron Kind (D) and James Sensenbrenner (R), both of Wisconsin, introduced a bill that would provide $35 million for CWD research and management; Montana Democrat Jon Tester introduced a companion Senate bill in December. “Honestly, it’s nowhere near enough,” Dunfee said of the proposed funding, “but it’s a darn good start.”

Along with helping states and tribes pay for surveillance, the bills could fund rapid-response efforts when CWD is first detected in an area—a strategy that appears to have kept New York State’s deer CWD-free after the disease was discovered there in 2005. The proposed funding could also support CWD research at a moment when some scientists say they’re on the cusp of developing transformative tools to fight the disease.

For example, Claudio Soto, a neurologist at the McGovern Medical School in Houston, says he has developed a blood test for the disease. Today’s CWD surveillance involves sampling brain and spinal tissue of dead animals; a reliable test for live deer could help farm and wildlife managers detect and respond to outbreaks more nimbly. But the USDA hasn’t approved the technique, and Dunfee said he’s skeptical. “Until now, no blood test has been developed that picks up prions reliably enough and at concentrations that are meaningful for management,” he said. “People have been trying to find that for a long time, and remember we’ve been working on other TSEs longer than CWD.”

Scientists also report progress toward preventing deer from catching CWD. In a 2014 paper, a New York University–led team announced what they said is the first successful vaccine for a prion disease. Five whitetail deer were given several doses of a vaccine made of Salmonella bacteria and a prion-like protein, then exposed to CWD. Four of them took longer than average to show signs of the disease, and the fifth never developed it during the study period.

“We are extremely close to slowing down the disease, that we know for sure,” said Fernando Goni, the NYU neurologist who led the study. Goni said his team has refined the vaccine so that it requires fewer doses and could be applied to deer food to inoculate wild herds, but he acknowledged that, given CWD’s vast and expanding range, doing so would be tremendously expensive.

Wildlife experts are also skeptical about a CWD vaccine. “Fifteen years ago, it seemed like there was an announcement every six months of someone saying, ‘This is it, we’ve got the vaccine candidate,’” Richards said. “And without exception, that was kind of the last you heard about it.” One potential vaccine developed by a Canadian company showed promise in early lab studies. But in a Wyoming field study, Richards pointed out, elk that were given the vaccine were nearly seven times more likely to develop CWD. And while a vaccine would be useful for protecting captive animals, using it in the wild would be a monumental undertaking, according to Dunfee. “Logistically, ask any wildlife biologist who’s tried to vaccinate wild herds and you’ll find it’s extremely difficult, if not impossible,” he said.   

Dunfee and others agree that more CWD research is important—perhaps it will yield a breakthrough to wipe out the disease. Meanwhile, politicians and the public need to recognize the seriousness of the disease, he said, and invest in containing it. “Prevention, prevention, prevention—that is the way we halt this disease,” he said. “If you can stop infected animals from moving to new areas, you can win this.”