Still Inscrutable, Chronic Wasting Disease Marches Steadily West

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Still Inscrutable, Chronic Wasting Disease Marches Steadily West

chronic wasting disease

A captive elk that has all the signs of CWD: emaciated, disoriented and listless. Photo Courtesy Wyoming Game and Fish Department/CWD Alliance.

Still Inscrutable, Chronic Wasting Disease Marches Steadily West
By Andrew McKean

Somebody inside the low-slung brick building that houses the National Wildlife Health Center in Madison, Wisc., has a grim but vital job.

They are responsible for updating the national CWD map, a digital graphic that tracks the spread of chronic wasting disease, an affliction of North America’s deer populations. Every time a new instance of the fatal neurological disease is confirmed, the federal employee adds another coordinate to the map that looks exactly like what it is: an epidemiological dot plot, on a continental scale. Each yellow or red point represents another CWD-positive animal in a game farm or deer-breeding operation. Each gray shade represents an expansion of CWD in wild, free-roaming ungulates, including elk, whitetails, mule deer, blacktailed deer, and moose.

chronic wasting disease

I’m paying especially close attention to the map these days, as my deer paradise of eastern Montana becomes a shrinking island of CWD-free real estate, and I wonder for how many more seasons I’ll have the original luxury of feeding my family venison uninfected by a brain-wasting disease that makes Alzheimer’s look almost humane in comparison.

Unconditionally fatal, untreatable, capable of lying dormant in soil for years, mysterious, arbitrary, and confounding, chronic wasting disease is arguably the greatest modern threat to America’s deer herd. Where its prevalence is especially high, it has shown the capability to depress local ungulate populations to an unrecoverable level. And it is slowly but inexorably marching westward.

But before you sell your deer rifle and all your camouflage, go steady. While there’s a lot we don’t know about CWD, there is plenty we do, including the fact that it moves slowly, that even in infected herds, most individual deer and elk are disease-free, its detection is possible with a few simple tests, there is no evidence that CWD-infected meat can infect humans who eat it, and hunters in many areas of the country have been living with CWD for decades.

But back to that map.

If you’re an elk or deer hunter—and that includes whitetails, mule, and blacktailed deer—you should familiarize yourself with the graphic, because it’s a good bet that those color codings will eventually converge on the place where you hunt. The map has splotches and dots in western Pennsylvania and upstate New York, a few more in Missouri and Michigan, and a big smear in Wisconsin before it jumps west and dominates the states of Colorado and Wyoming, with tendrils extending into Nebraska, Kansas, and Utah. North of the 49th Parallel, there’s a significant concentration of CWD in southern Saskatchewan and Alberta.

Hunters in the places where CWD has been confirmed know this fact: You’re better off with wolves, occasional hemorrhagic disease, or periodic winterkill than with CWD, which kills every animal it infects and can lay dormant for years until it expresses itself again. That expression is gruesome. CWD-positive animals lose their appetites, become disoriented and listless, and in the final stages of the disease, drool excessively and stagger around until they die in an emaciated, helpless state of physical and mental vacancy.

“Death is inevitable,” says the NWHC website, the repository for all CWD-related research and public information. If predators don’t kill CWD-positive animals, then they either die lonely, agonizing deaths or they’re killed by licensed human hunters who then must ask a fundamental question: Do I feed potentially infected venison to my family?


As of mid 2018, CWD had not been detected in states west of Montana. That includes Idaho, Oregon, Washington, California, Nevada, and Arizona, as well as British Columbia. Because of its geography and its public policy (more on this in a bit), the West isn’t at high risk of the disease, but that’s cold comfort considering many Western states—including my Montana—also felt they were more or less immune from CWD. Then they went looking for it.

The origin of the disease is as debatable as the vectors of its transmission, but we know that it first showed up in the late 1960s in northern Colorado, in a research facility where mule deer were confined for a forage and nutritional study. The facility also contained a population of domestic sheep that tested positive for scrapie, a brain-wasting disease similar to CWD. There is some evidence that scrapie jumped the species barrier in the facility. Exactly how that happened is unclear, just as it’s unclear how the disease escaped the facility. What is even more clear is that once CWD entered the game-farm pipeline, it spread around the country in a pattern that correlates with captive deer facilities.

“There certainly seems to be a link between transporting deer and the spread of CWD,” says Dr. Grant Woods, a biologist, land-management consultant, and host of Growing Deer TV. He notes that the detection of CWD among wild populations of deer and elk (the gray shading on our map) is in counties near game farms and high-fence deer shooting operations (the yellow and red dots).

One of the first and best defenses against CWD seems to be to stop transporting deer from one place to another, whether live in the back of a stock trailer or dead in the beds of hunters’ pickups. The other defense is early detection, and that brings me back to my home state, and the most recent and relevant model for how CWD response is likely to play out in your Western state.


If you study that CWD distribution map, you’ll notice two big concentrations of the disease west of the Mississippi, in southern Canada’s Grain Belt, and in Wyoming. What’s between those two? Montana, where I live.

Montana has been officially CWD-free since 1998, when it was detected in captive elk on a game farm in the western part of the state. That game farm was “depopulated,” as the eradication of animals is euphemistically called, a ballot initiative was passed banning future game farms, and the state’s deer and elk hunters breathed easier, figuring we had dodged the CWD bullet that, at the same time, was decimating Wisconsin’s wild whitetail herd.

chronic wasting disease

CWD first showed up in the late 1960s in northern Colorado. It is now arguably the greatest modern threat to America’s deer herd. Photo Courtesy Wyoming Game and Fish Department/CWD Alliance.

But we Montanans have been watching CWD creep closer from the south and the north. Montana’s Fish, Wildlife & Parks Department (FWP) has, too, and after years of ambivalence about CWD, FWP last year launched an intensive monitoring campaign on its border with Wyoming. Both shockingly and somewhat unsurprisingly, the disease was detected in two mule deer south of Billings.

The detection triggered a response that had been planned for years. There are two models for CWD response and management. One is Wisconsin’s, which was to draw a radius around detection areas and eradicate every deer within it, with or without landowners’ permission. Then there’s Wyoming’s model, which is to sample for CWD but then to basically track its spread, with little depopulation of affected herds. Montana has tried to strike a middle ground.

chronic wasting disease

It is believed that CWD is spread from game farms and high-fence shooting operations to wild populations of deer and elk. Photo Courtesy Wyoming Game and Fish Department/CWD Alliance.

The first step is to establish prevalence, or how extensively the disease has spread through the deer population. In order to do that, the state established a special late season and issued tags to hunters to kill a number of deer—around 325—in the CWD-positive area. Samples from all those deer, plus even more killed during the 2017 general season, were tested, and 10 came back as positive.

“That works out to 2 percent overall prevalence in the deer herds tested,” says Emily Almberg, a Montana Fish, Wildlife & Parks researcher. “Broken down by species, the prevalence in mule deer was 2 percent while the prevalence in white-tailed deer was 1 percent.”

That’s manageable, say most CWD experts, who say the trigger to activate more aggressive containment to control the disease is when more than 5 percent of the herd is infected. More troubling is that within a core of the Montana hunting area, prevalence is closer to 10 percent. The state is still mulling what to do to manage the disease in that portion of the hunting district.

But back to me and my hunting area. Montana FWP is moving its surveillance to the northern border this fall. That’s my neck of the woods, and we will see CWD sampling stations set up along the Canadian border starting in September. I have no doubt it will be detected. After all, based on that national map, I assume we’ve had CWD-positive animals in our area for years. But when a sample test does come back positive, here are the handful of things we know will happen.

First, there will be prevalence testing in the affected area, using either general-season tags or a special CWD hunt to collect and test a statistically valid sample of the population. Second, there will be transportation restrictions, prohibiting the movement of whole animals—or even brain and spinal tissue—from the affected area. Third, people who get their animals tested will need to process the meat and mark the packages in a distinctive way. If a test comes back positive—it takes a few weeks to get results—the hunters will be advised to dispose of the meat. Commercial butchers in affected areas are discouraged from grinding meat in batches, or dumping meat from multiple hunters’ game in a single grind.

There is no known transmission of CWD to humans, but disease experts recommend that humans do not consume meat from CWD-positive animals. After all, before the disease jumped the species barrier, it was thought that scrapie couldn’t be transmitted to ungulates. And epidemiologists note that CWD is in the same family as bovine spongiform encephalopathy, or BSE, better known as mad-cow disease that did infect humans who ate meat from diseased cattle.


If you live in a state where CWD hadn’t been detected, be thankful. But don’t be complacent. There are a few things you can do to delay its arrival.

First, advocate your legislature and wildlife and livestock commissions for better regulation of game farms. There seems to be some evidence that CWD is spread when ungulates eat the brain tissue of affected animals. In the wild, that almost never happens, but high-fence operations often feed animals meal made from the ground bones and tissue of ungulates. Deer farms and high-fence shooting operations haven’t made much inroad in the West, and this is a good enough reason to keep them from becoming established.

Chronic wasting disease

One of the best defenses against CWD seems to be to stop transporting deer from one place to another. Pictured is a head drop off station for elk in Wyoming. Moose Henderson Photo.

Also, support prohibitions on feeding wildlife. Wisconsin’s CWD outbreak was probably intensified by the custom of feeding game, which unnaturally concentrated animals around bait sites and led to increased contact between infected and non-infected animals.

Second, get accustomed to deboning your trophy in the field and leaving as much bone, spinal fluid, and brain matter as possible in the specific area where you killed it. There is little danger of CWD being present in clean venison. And then when you process your meat—either yourself or at a commercial butcher—make sure you clearly label the packages with sex, species, date, and area where it was killed. That will make identifying the meat easy in case CWD is detected in the area where you hunted.

Advocate for more funding for CWD research and response. Most state game agencies are strapped with their workaday mandates of monitoring wildlife, catching poachers, and licensing hunters. Monitoring and sampling for CWD is expensive, and a bill in Congress aims to help. Senate Bill 2252, the “Chronic Wasting Disease Support for States Act,” would make available $35 million annually in federal funds, to be split between states ($20 million), tribes ($5 million), and a rapid-response fund that states or tribes could tap when CWD is detected inside their borders.

Lastly, keep abreast of CWD’s advance. While you certainly don’t want it to show up where you hunt, knowing about how it affects animals, how to identify it, and knowing what to do if it does arrive make the unknowns about the disease a little less unsettling.

CWD in Your State?
Most state game agencies have developed CWD action plans in case the disease shows up. Here are the plans of several states:



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