Nelson Issue Brief: Deer – Hunting, Ecology and Chronic Wasting Disease

CWD Prevalance and Transmission

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Tim Van Deelen, Professor, Forest and Wildlife Ecology, UW–Madison,

Chronic wasting disease (CWD) is well-established in southern Wisconsin and is spreading. Where established, CWD’s prevalence is accelerating each year, and is higher in male deer and in older deer. Recent data suggested that prevalence among males who are more than four years old is nearly 50 percent in portions of south-central Wisconsin endemic areas. Research suggests that transmission occurs through both direct contact (deer-to-deer) and through the environment (where the disease agent persists in the soil and is taken up in plants), but that direct contact appears to be the most important transmission mechanism.

Our research in collaboration with the Wisconsin Department of Natural Resources (WDNR) and U.S. Geological Survey finds that CWD causes the growth rates of infected deer populations to decline as prevalence increases. Year-to-year survival is greatly reduced among radio-collared Wisconsin deer that test positive for CWD when compared to deer that test negative.

Line graph showing increase in CWD prevalance in the last 15 years

CWD prevalance increases dramatically as deer age, and has been increasing rapidly over the last 15 years. Sample size was restricted to in-season hunter-killed deer. Credit: Data from Wisconsin DNR

Moreover, we find that CWD-positive deer may not die from the disease directly. Rather, CWD enhances mortality risks from the many other sources of mortality that deer routinely experience, such as predators and car-deer collisions. The effect on growth rates is particularly concerning, because sustainable hunting requires a deer population that is adding individuals somewhat faster than it is losing them.

Unfortunately, there are few options for managing endemic CWD outbreaks, and those that we have are expensive and controversial. Therefore, prevention, containment, and early detection are vitally important.

The testing of hunter-killed deer provides essential information for tracking changes in prevalence, changes in age- and sex-related patterns of infection; in short it allows us to map the extent of Wisconsin’s CWD outbreak. Testing is also important for being informed consumers of venison. The World Health Organization and the Centers for Disease Control both recommend that people not consume venison from deer that test positive for CWD.

Hunters and landowners can assist in the management of CWD by:

  1. Reporting sickly looking deer to WDNR
  2. Participating in the WDNR’s CWD testing program
  3. Participating in deer hunting to remove deer that are at highest risk for infection (older males) and to reduce the population generally
  4. Adhering to guidelines for butchering wild deer (bone out the meat, do not cut into spine or lymph nodes)
  5. Disposing of potentially infectious bones, meat scraps, and offal in sanitary landfills
  6. Avoiding moving deer and deer tissues
  7. Refraining from baiting and feeding or otherwise concentrating wild deer
  8. Making livestock mineral licks inaccessible to deer

Learn more about deer-related research at UW-Madison