What is Chronic Wasting Disease (CWD) and how does it affect hunting? Unless you live under a rock, you’ve heard about CWD. But, unless you’re a microbiologist, you may not know exactly what causes CWD or how it moves around the environment or within an infected animal. And, unless CWD has been detected near where you live or hunt, you may not know much about it at all.
(Photo Caption and Credit: Colorado is one state with mandatory chronic wasting disease testing in selected GMUs. Photo Credit David Hannigan)
CWD is categorized as a spongiform encephalopathy, an unnecessarily scientific term meaning that it causes sponge-like holes in brain tissues of infected animals. Other spongiform encephalopathy diseases include scrapie in sheep and goats, BSE or mad cow disease in cattle and a rare human form known as Creutzfeldt – Jakob disease. All spongiform encephalopathies are caused by microscopic misfolded protein strings known as prions. CWD affects members of the deer family, including elk, mule and whitetail deer, moose, reindeer and presumably caribou. Symptoms of advanced CWD include a severe loss of weight and body condition, neurological problems such as wobbly or depressed posture, uncoordinated walking and excessive salivation. However, some animals in early stages may appear normal. CWD is ultimately fatal to infected animals, although many times an infected animal dies of another cause, such as predation, road kill or another accident.
Prions, by definition, are pathogenic protein strands that are incredibly resistant to environmental forces. Prions are duplicated in the infected animals, and they are shed in feces and saliva, and ultimately, they are deposited in soil when the animal dies. Prions can be ingested by predators and scavengers and can be moved around the landscape by these animals (they have not yet been shown to affect predators or scavengers). Prions have also been documented to be picked up by some plants, meaning that a deer or elk grazing on grass can pick up the prion left there by another animal. Prions are not destroyed by chemicals or heat (they can withstand temperatures in excess of 800 degrees F) and it appears they can remain in soil for decades and still be infective.
CWD was first documented as a syndrome in northern Colorado in 1967, but it wasn’t known what caused it until 1978. Since that time, it has been documented in wild cervids in 23 states and in captive deer in 16 states. It has also been found in Canada, South Korea (in imported elk from Canada), reindeer in Norway and an elk in Finland.
Prions enter a deer through contact with another infected animal, such as nose-to-nose contact or through ingestion of infected material, such as soil or deer feed. Once inside the animal, prions move about somewhat unpredictably, and the genetic make-up of the deer sometimes affects the rate at which an animal shows the infection. Ultimately, prions concentrate in nervous tissue, such as the brain and spinal tissue, though prions also have been found in myelin sheaths in muscle tissue. While the best test for prions involves removing lymph nodes from the throat area or the brain stem (both can only be performed on dead animals) a live-animal biopsy shows some promise. The difficulty with the biopsy test is that newly infected animals may test negative at first, though they may become infective later.
Wildlife agencies are very concerned about CWD for several reasons. First, anything that threatens the health of the wildlife resource is a concern, and CWD not only affects individual deer, but it appears to progress through deer herds, reducing survival and decreasing herd numbers. In some areas where the disease has been present for many years, the deer herd is declining and hunting is definitely impacted. Second, once discovered, agencies have to spend an enormous amount of money and energy conducting surveillance, holding meetings and developing plans for management. Third, anything that undermines hunter confidence can affect the very base of conservation funding. If only 10% of today’s hunters stopped hunting due to CWD concerns, funding would be inadequate for all of the agencies.
The presence of CWD causes wildlife agencies to adopt strict regulations about movement of live deer (as might happen between deer farms or an elk transplant) and deer carcasses. It has also caused agencies to amend regulations concerning hunting methods. Some methods, such as baiting deer, concentrates deer together, which can spread CWD faster than might otherwise occur. Banning artificial feeding, including baiting as a hunting method, is a common regulation to prevent the spread of CWD.
Hunters need to understand CWD and the associated regulations when hunting in affected areas or when traveling to a hunt. First, while CWD prions have not been shown to affect humans, the Center for Disease Control recommends hunters not eat meat from an animal known to be infected with CWD. Most states offer some type of testing and in areas known to be infected, mandatory testing may be required. Infection rates in any given year are usually low- 4% to 20%- but if you’re hunting in an area known to have CWD it always pays to have your deer or elk tested. It also stands to reason that you not harvest an animal that exhibits symptoms of severe infection. You should always take precautions when dressing any game (latex gloves, prevent any blood or fluids from getting in your eyes, wash yourself and your knives with soap and water afterwards), but this may be especially important when hunting in a CWD area.
To prevent the movement of prion infected tissues, most states now require any carcass being moved to exclude brain and spinal tissue. Boned-out meat, wrapped and packaged meat and quarters without any spine attached are approved for movement. Also, cleaned antlers and skull caps, without brain tissue or meat attached, can be moved as can hides and capes. Cleaned elk ivories and any finished taxidermy can also be moved without restrictions. The same precautions also exist for anyone hunting susceptible exotic species such as red or sika deer. Interestingly, some deer species, such as fallow and axis deer appear immune to CWD prions through normal environmental routes.
Because game wardens don’t know what part of Wyoming (or any other state) may be a CWD state, it’s best to follow these movement restrictions any time you hunt deer or elk out of state. Remember that restrictions will also exist for any state that you’re driving through, and agencies have started monitoring deer hunters using interstate highways during deer seasons to prevent the movement of whole carcasses.
The more you know and understand about CWD, the more reasonable the restrictions appear. None of us are likely to give up hunting, but we also don’t want to be responsible for spreading a disease. Plan your hunt in 2018 with CWD as a part of the process: learn to bone out the meat, find out if mandatory testing is required, and pay attention to agency regulations. CWD will be around for the rest of our hunting careers, but it should not affect your decision to hunt.
About the Author: Mike Bodenchuk is a professional wildlife biologist specializing in wildlife conflict resolution since 1979. He has managed wildlife projects and properties in several US states and in Mexico. He has also traveled extensively, lecturing and instructing on wildlife management techniques in Australia, Brazil, Canada, Great Britain, Mexico, Laos, South Africa, Spain and Ukraine. Mike describes himself as a “recovering outfitter,” having guided for big game professionally from 1980-1991 in New Mexico and Texas. Along the way, Mike has personally hunted in 26 states, Australia, South Africa and the UK. Mike has authored or coauthored over 50 scientific papers, four book chapters and hundreds of popular articles on wildlife management and hunting. His professional interests include predation management and feral swine control while his personal interests center around hunting and his family. Mike’s entire family is engaged with the hunting industry in some form: his wife Debby is a wildlife artist and taxidermist; his son Hunter is a wildlife photographer, government trapper and a licensed hunting guide; and his daughter Leigh Ann is also a wildlife biologist. Collectively, they apply for around 100 permits, points or licenses each year and they always have a new adventure on the horizon.
Photo Caption and Credit: Colorado is one state with mandatory chronic wasting disease testing in selected GMUs. Photo Credit David Hannigan