Chronic wasting disease: forgotten, but not gone

 

As an environmental journalist, I know full well how difficult it can be to get people interested in a creeping problem. Climate change is a perfect example—its effects are hard to pin down and slow to develop. Wildfire, on the other hand, is dramatic, deadly and easily identifiable as a problem, especially if your house burns down. Climate change news doesn’t break, journalists joke: it oozes.

Wildlife diseases are the same way. Those that dramatically wipe out entire populations—think white nose syndrome in bats or chytrid fungus in amphibians—garner much more media coverage than ailments like chronic wasting disease, which affects elk, deer and moose. CWD takes years to kill a single infected individual and has yet to completely decimate an entire herd. “I’ve heard it called an epidemic in slow motion,” says Christopher Johnson, a research biologist at the National Wildlife Health Center in Wisconsin.

Despite CWD’s slow pace, the disease isn’t going away: since being identified in captive mule deer in northern Colorado in 1967, it has spread to 19 states and in Wyoming, close to 40 percent of deer in the eastern half of the state are infected, up from 15 percent in 1997. One mule deer herd in particular has a 50 percent infection rate for males, the highest known prevalence in all of North America. Now, researchers studying that herd say they’re finally getting to a point where they can document how CWD slowly destroys an entire population, not just individuals. The preliminary findings aren’t good: the herd’s size has been cut in half in the past 12 years, and the drop seems to be related to CWD-induced deaths, says Melia DeVivo, a PhD student at University of Wyoming.

Yet there seems to be little general interest in CWD, and researchers say federal funding has decreased in recent years even as infection rates rise. “The negative effects aren’t in your face immediately,” DeVivo says, but “it is going to really hurt some of these populations if not completely wipe them out.”

CWD is a strange disease. It incubates inside infected deer, elk or moose for years before symptoms show up. The disease is carried by prions, an infectious protein that attacks the brain, which cause infected animals to lose their appetite. As they slowly starve, they begin to display weird behaviors: pacing, walking with their heads lowered, drooling and stumbling.

Because CWD takes so long to manifest itself, it’s difficult to manage. The state of Wisconsin took an especially aggressive approach and tried to kill off most of its infected deer, creating longer hunting seasons and requiring hunters to kill a doe before shooting a buck, but the disease still spread. That’s because prions persist for years in the environment, says Johnson. They build up, and even amplify, in soil, infecting deer, elk and moose as they graze, and may even be taken up by the plants themselves. They linger in the feces and bodily fluids of infected animals and inside their carcasses after they die. Researchers are now studying whether other animals that eat the dead deer, like mice or voles, can get sick, too.

At the moment, the scientific consensus says the risk of humans getting the disease is low, even among people who eat contaminated meat. But that's still not a good idea, and many state wildlife agencies caution hunters not to shoot sick-looking animals and encourage them to minimize contact with brain and spinal tissues and get their meat tested. And according to the Centers for Disease Control and Prevention, “because of the long time between exposure to CWD and the development of disease, many years of continued follow-up are required to be able to say what the risk, if any, of CWD is to humans.”

I wondered how much hunters worry about the disease, so I called Susan Smith, owner of Paonia, Colo.’s wild game processing shop, to ask. We’re in the thick of hunting season in Western Colorado, and pickup trucks full of guys in camo or day-glo orange frequently rumble down the main street. Do people think about CWD, I asked? “A few do, most don’t,” she said, adding that hunters used to ask for their meat to be tested more often, but don’t as much anymore. Scott Edburg, assistant chief of the wildlife division at Wyoming Game and Fish, has seen a similar slump in interest among Wyoming hunters.

Why are people less concerned about CWD now, when it’s clear that infection rates are rising? “Cause they’re not reading about it in the newspaper every day,” says Michael Miller, senior wildlife veterinarian with Colorado Parks and Wildlife. “Part of the problem, to be quite honest, is we know it’s there, we kind of have this nagging suspicion that it’s having some effect, but it’s been really hard to point to something clear. And we really don’t have a lot we can do about it.”

Plus, previous efforts to control CWD were really unpopular. In the early 2000s, Colorado, like Wisconsin, tried to cull its deer population, but the public protested. “They didn’t see the clear effects of the disease on deer abundance,” Miller says, “but they saw the effects of our management on deer abundance.” After a few years, the culling stopped.

The most recent state to discover infected deer was Pennsylvania. Last March, according to The Altoona Mirror, hunters turned a middle school auditorium “into a sea of camouflage” during a presentation from the state’s Game Commission about how to manage CWD. "There is no place where this disease has ever occurred that it has been stopped," said Walt Cottrell, a veterinarian for the Pennsylvania Game Commission. "There are two things the disease does when it arrives: It gets worse, and it spreads."

And, eventually, it fades into the background, like so many other creeping environmental problems.

Emily Guerin is a correspondent at High Country News. She tweets @guerinemily.

Map courtesy USDA-APHIS.

Photo courtesy Greg Westfall via Flickr creative commons.