CWD affects you as a hunter. In some areas, CWD means temporarily increased hunting opportunities followed by decreased opportunities. CWD will affect age-class in many deer populations. CWD already affects how you can transport your deer (or elk) across state lines, with legal consequences for violators. And of course, CWD may affect your decisions about processing and eating venison. Contributing editor and wildlife biologist Mike Bodenchuk has followed CWD research and developments his whole career. HuntingLife asked him to give our readers an in-depth review on CWD: what it is; what researchers know; what hunters need to know; and how it can affect wildlife populations, hunting opportunities and the future of hunting in North America. Here is Mike’s first of four reports.
What Is CWD?
Veterinary pathologists classify Chronic Wasting Disease (CWD) as a Transmissible Spongiform Encephalopathy (TSE), which puts it in the same category as “Mad Cow Disease” (technically Bovine Spongiform Encephalopathy or BSE) and “scrapie,” which affects sheep and goats. TSE’s are so named because they ultimately form lesions in the brain of infected animals, which look like a sponge under a microscope. Chronic Wasting Disease is a TSE that affects members of the cervid (deer) family. It is known to affect whitetail and mule deer, elk and moose, and in other countries it has been diagnosed in reindeer (caribou). It can or should also affect red deer and sika, but under normal field conditions it does not affect other common exotic deer such as axis or fallow deer.
CWD was first diagnosed in 1967 as a wasting syndrome in Colorado mule deer but was not identified as a TSE until 1978. After a lot of research, scientists have identified the cause of CWD as a specific “prion,” which is a type of mis-folded protein. Prions, by definition, are pathogenic and are extremely resistant to environmental factors. Prions replicate in the body of affected animals and concentrate in nervous tissue such as the brain and spinal tissues but have been identified in muscle sheaths and other tissues. They are spread in urine, feces and nose-to-nose contact between animals. However, prions survive digestion in predators and scavengers and can be spread through the environment through these animals feeding on an infected carcass. Prions also survive for a very long time (more than 40 years) in soil and can be picked up from soil by the roots of some plants and transferred to animals grazing on those plants.
In the latter stages of the disease, the symptoms of an infected deer or elk include extreme lethargy, reduced feeding, which leads to emaciated animals (hence the “wasting” part of the name), aimless wandering, drooping heads and excessive salivating. In the wild, these symptoms are rarely seen because infected animals are more prone to other forms of mortality before they actually die of the disease. Even in the early stages of the disease, a deer with CWD may be a little slower and therefore easier for a predator to catch or more prone to a vehicle collision.
Within the animal, CWD ultimately will be fatal, either directly from degradation of the brain tissue or indirectly through predation, winter starvation or accident. Within an infected population, CWD appears to increase in prevalence with some herds having infection rates of 20% or more. While some management actions, such as aggressive harvest, appear to slow the progression of the disease through a population in some cases, some deer herds are experiencing long-term declines of 40% or more.
Is it Safe to Eat CWD Infected Deer?
Just as the prions don’t affect predators or scavengers, there is no evidence that CWD prions will affect humans who eat deer meat. However, in one study, prion infected tissue was fed to monkeys which then contracted a separate form of Spongiform Encephalopathy, suggesting that transmission could become an issue. Scientists are cautious, and the Center for Disease Control and Prevention advises against consuming an infected deer or elk.
CWD has been identified in wild deer or elk in 23 US states and two Canadian provinces. It has also been identified in captive deer or elk in 16 states and three provinces. Initially, there was a lot of speculation regarding the role of captive deer in CWD movement. The “gold standard” test to find prions in deer or elk are post-mortem biopsies of lymph nodes, which precludes testing live deer prior to movement. Only recently have live animal tests become accurate enough to be considered reliable. However, since there appears to be a large amount of variability in how fast prions travel through the body of a deer (including some genetic factors), live animal tests may not catch a recently infected animal.
How Can CWD Affect Hunting?
Hunters’ interests are affected by CWD in a number of ways. Directly, hunters should be aware of CWD and suspicious of deer exhibiting the symptoms. Because CWD prions can be moved from one area to another with carcass transport, most states have put restrictions on carcass movement to preclude moving spinal or brain tissue. Other hunting restrictions vary from state to state, but include bans on deer feeding or baiting (to prevent concentrations of deer, which could accelerate prion contact rates), prohibitions on use of deer urine or some deer scents and mandatory or voluntary testing of deer or elk taken in suspect areas.
Indirectly, there have been discussions on the best management strategies and additional hunting seasons have been implemented in some states to increase surveillance or to reduce populations. In many whitetail states, high populations of deer may serve to increase the opportunity for prions to spread through the population. Expect managers to intentionally reduce populations through increased opportunity and even agency sharpshooting if populations are too high.
Another area being discussed is the reduction of average age class of deer. CWD prions act on a deer slowly and an infected deer may live one to three years, possibly shedding infected saliva through its life. This is especially true in the southern states where winter stress is lower. Trophy management calls for an older age class and deer managers have spent a lot of time getting hunters to concentrate on older bucks. With CWD in a population, a better disease management strategy might be to increase the harvest on younger deer to reduce the accumulation of prions and have a quicker turn-over of the population. While still experimental, this strategy is being applied in a number of cases. Time will tell if it is successful.
One agency concern is that hunters will stop hunting deer. In many states, the only management option for agencies is to have hunters harvest deer. Agency budgets are based on license sales and a reduction in license sales also affects Federal matching funds for management projects and Wildlife Management Area purchases. This disease has the potential to be the perfect storm for state wildlife agencies: increased costs associated with surveillance and management coupled with decreasing funding and a decreased interest in hunting deer – the only option available. In future articles, we’ll examine what hunters can do in the field, in transporting a deer or elk and while processing your meat.