I used to love watching Boston Legal on TV, in which William Shatner plays Denny Crane, the loony head of a law firm who occasionally claims to have mad cow disease. While guffaw-funny at the time, the group of diseases that mad cow disease belongs to, Transmissible Spongiform Encephalopathies (TSEs), is not.
Caused by prions (or non-living protein infectious particles), TSEs are scary because they cannot be metabolized and so accumulate in the brain where they cause holes that give the appearance of a “sponge”. Not to sound too alarming, TSEs have long incubation periods that may be years before clinical signs of disease are evident, but the end result is always death in the host.
One kind of TSE that has shown up in wildlife in the Lower 48 and Canada is chronic wasting disease (CWD). CWD was first documented in captive mule deer at a Colorado research facility in 1967. By 1981, it was detected in free-ranging mule deer and elk populations in nearby Rocky Mountain National Park. By 2002, CWD had moved east to white-tailed deer in Wisconsin and by 2011 had made it to the East Coast in Maryland.
It is now known to infect wild populations of elk, mule deer, white-tailed deer, black-tailed deer, and moose. Currently, CWD occurs in Colorado, Illinois, Kansas, Maryland, Michigan, Minnesota, Montana, North Dakota, Nebraska, New Mexico, New York, Oklahoma, South Dakota, Utah, Virginia, and West Virginia, as well as Saskatchewan and Alberta in Canada.
The good news is that CWD does NOT occur in Alaska. The bad news is that last week, CWD was confirmed in a road-killed moose from southern Alberta, the first time that moose have tested positive for CWD in Canada!
The origin of CWD is unknown, but transmission is likely lateral (animal to animal) by saliva, feces, urine and nervous/lyphoid tissues. Passing from mother to offspring may occur, but this mode appears to be relatively unimportant from an epidemiological perspective. Recent research indicates that prions can be excreted by deer and elk, and then transmitted by eating grass growing in contaminated soil. Experimental work published in 2012 shows that carrion birds such as American crows can carry infectious prions in their gut, which can then be passed through their droppings. And prions are very resistant to environmental degradation, persisting for decades in soil.
Most cases of CWD occur in adult animals. The most obvious and consistent clinical sign of CWD is weight loss over time, hence the name “chronic wasting.” Behavioral changes also occur in most cases, including listlessness, lowering of the head, droopy ears, stumbling or tremors, and a smell like rotting meat. Once an animal starts manifesting signs of CWD, it may be only weeks or months before death.
The Alaska Department of Fish and Game (ADF&G) has been monitoring for CWD in free-ranging wildlife populations since 2003. They’ve tested almost 2,000 Sitka black-tailed deer, 659 moose, 87 caribou, and 90 elk, including 42 moose killed by vehicle collisions recently on the Kenai Peninsula. What’s unusual about CWD is that there isn’t any way to detect it in live animals — it has to be done post-mortem. To date, all samples have tested negative for CWD. The ADF&G maintains an excellent website on CWD with up-to-date test results.
In 2013, ADF&G will focus on moose dying within 5 miles of captive elk facilities. On the Kenai Peninsula, this effort will include areas near Soldotna and Homer in Game Management Unit 15.
Risk of transmission to humans appears to be low, but that risk cannot be dismissed. The Centers for Disease Control and World Health Organization (WHO) state that there is no scientific evidence that CWD causes human illness. However, WHO and some State health agencies recommend that no part of an animal known to have CWD be consumed by humans and that safe handling and processing procedures are followed.
The ADF&G offers several precautions to minimize the spread of CWD into Alaska: Do not handle, harvest or consume wild animals that appear sick, wear rubber gloves when field dressing carcasses, minimize handling of brain and spinal tissues, bone out carcasses on site, do not bring unprocessed carcasses or heads of deer, elk or moose from Outside, do not use elk carcasses for bear baiting, and do not use urine-based scent lures (now prohibited by regulation). The latter has now got me wondering about spraying commercial blood and urine products on ornamentals to reduce browsing by moose and deer.
At the end of the day, CWD is no different than any of the other exotic and injurious plants, animals or diseases that are slipping across our borders into Alaska. This very telling narrative was extracted from the Wisconsin Department of Natural Resources’ CWD Response Plan: “After more than eight years of CWD management in Wisconsin, it is increasingly clear that controlling CWD in Wisconsin’s free-ranging white-tailed deer will be extremely challenging and will require a commitment of human and financial resources over an extended period of time.” Perhaps we can learn from their experience and do all that is possible to prevent this from happening in Alaska. Besides, mad cow disease is only funny on TV.
John Morton is the Supervisory Biologist at Kenai National Wildlife Refuge. ‘Like’ the Refuge on Facebook to stay connected with upcoming events, news and recreation updates at www.facebook.com/kenainationalwildliferefuge .