Chronic wasting disease (CWD) is an emerging infectious disease of North America’s deer family species. Since the early 1980s, when it was first detected in wild, free-ranging animals in Colorado and Wyoming, the disease has spread to mule deer, white-tailed deer, and elk in 22 US states and 2 Canadian provinces. More recently it has infected wild moose. Experimental work suggests that caribou, the continent’s only other deer species, may also be susceptible.
This is a particularly nasty disease for several reasons:
- Once clinical signs of the disease appear, infected animals always die.
- The disease is transmissible by animal-to-animal contact but also indirectly when environments become contaminated with the disease-causing agent, called a prion. Infected animals continue to shed infectious prions for months until they die.
- Populations of susceptible animals have shown no indications of developing immunity to the disease. The disease agent, or pathogen, that causes CWD is a protein particle that contains no DNA, thus failing to illicit an immune response in susceptible hosts following infection.
Any disease that is infectious, transmissible, and causes mortality is of concern to wildlife managers and to conservationists alike. But a disease that’s 100% fatal and to which whole populations may be susceptible is simply frightening.
The only good news here is that CWD spreads relatively slowly among animals once a population of deer of elk becomes infected. However, a new publication in the Journal of Wildlife Management is anything but comforting about the trajectory of the disease over the course of an epidemic. Ryan Manello and his coauthors studied the effects of CWD on the elk population that spends much of the year in Colorado’s Rocky Mountain National Park. Their paper summarizes a good deal of our current knowledge about CWD’s impacts on deer and elk herds, and reports the following on their study of Colorado elk:
“We found CWD-caused mortality can exceed natural sources [predation, accidents, and other diseases] and, at the rates observed in our study, could result in either an unsustainable population or necessitate declines in hunter harvest.”
They note, as have other authors on the subject of CWD’s impacts on populations, that increased densities of animals likely exacerbate transmission, infection, and mortality attributable to CWD. And this is of particular concern in regard to the 22,000 elk of western Wyoming that are crowded onto winter feedgrounds for 6 months each year. Their densities far exceed those in Rocky Mountain National Park or any other wild elk herds. And we know from the history of wildlife ranching (where elk are confined in fenced enclosures) herd infections can exceed 50 percent, requiring the killing of entire herds to rid these privately-farmed elk of CWD.
CWD is a serious threat to our public herds of deer, elk, and moose. The story of how this disease epidemic will progress is still unfolding. There’s no instance of the disease diminishing in any herds that have become infected, even after 25-30 years.
In artificially crowded conditions, such as western Wyoming’s elk feedgrounds, prospects for the health and conservation of these precious resources are truly in doubt. As CWD marches ever closer to those elk (it’s now infected deer and moose within 45 miles of the elk feedgrounds and also Yellowstone National Park), time is growing short to implement management that will lessen the disease’s impact.
First and foremost, many disease experts recommend ending Wyoming’s unnecessary feeding programs, which would require reducing the artificially high numbers of elk. The Wildlife Society, a professional society of 11,000 wildlife scientists, managers and educators, likewise has advocated that both government agencies and the general pubic should phase out the feeding of wild ungulates (hoofed animals) to reduce the spread and impacts of CWD and other diseases.
For a summary of how artificial feeding will likely exacerbate the effects of CWD on wild populations, see “Elk Winter Feeding = Disease Facilitation” in The Wildlife Professional.