Managing Chronic Wasting Disease

The Minnesota Department of Natural Resources has confirmed that an adult female deer harvested during the 2010 hunting season has been diagnosed with Chronic Wasting Disease (CWD), a brain and nervous system disorder found in deer, elk and moose. This is disappointing news but the DNR is well prepared to address it.

The discovery occurred the week of Jan. 10, 2011, during laboratory analysis of more than 500 samples (lymph nodes) taken from hunter-harvested deer taken within a 20-mile radius of Pine Island in southeastern Minnesota. Initial screening of all other samples is complete. The DNR collects and evaluates lymph nodes because CWD can be detected through microscopic analysis.

The National Veterinary Services Laboratory in Ames, Iowa, confirmed the University of Minnesota's preliminary diagnosis of the single adult female white-tailed deer on Jan. 25, 2011.

If the preliminary finding is confirmed by NVSL, this will mark the first time CWD has been found in wild deer in Minnesota. Though the disease has been detected in Minnesota on four previous occasions since 2002, all of the instances involved "captive cervids", meaning domestic deer or elk confined to a fenced-in commercial operation.

At this point, no one knows. In fact, we may never know. What is known is that the "presumed positive" deer was harvested about three miles southwest of a former domestic elk farm near Pine Island. The farm's elk herd was depopulated after a seven-year-old female elk tested positive for CWD in January 2009. Three additional elk were found to be infected with CWD during the depopulation effort. The closest wild deer with CWD in Wisconsin is 150 miles from the location this CWD-suspect deer was harvested in Minnesota.

CWD is found in wild deer, elk or moose in 14 other states and two Canadian provinces, including the Midwestern states of Wisconsin, Illinois, North Dakota and South Dakota. For specifics, visit the CWD Alliance Website.

The DNR has done much to prevent CWD from entering Minnesota's wild deer herd. For many years the agency has worked closely with the Minnesota Board of Animal Health (the regulators of domestic deer and elk farms) on policies, procedures, and statutes to protect wild deer from coming into contact with commercially-raised elk and deer. The agency has also worked with the state Legislature to create animal transportation laws that minimize the risk of CWD from entering the state. For example, whole deer, elk, caribou or moose carcasses from other states or provinces may not be brought into Minnesota from areas known to have CWD in the wild.

The DNR has been actively on the lookout for CWD since 2002 when the disease was first found in a domestic elk farm in central Minnesota. The agency has been actively looking for the disease because an important management strategy is early detection. Since 2002, the DNR has tested more than 32,000 hunter-harvested or road-killed deer, 60 elk and and 90 moose in the name of early CWD detection. Until now, laboratory analysis had never found a wild deer "presumed positive" for CWD.

Yes. It is a logical place to look because it's an area where CWD was recently discovered. The DNR collected 515 deer lymph node samples during the past deer season. This followed the collection of 934 deer from the same area in 2009. All of these deer were taken within a 25-mile radius of Pine Island. The DNR obtained these samples from hunters who voluntarily allowed DNR staff, University of Minnesota veterinary students and other experts to extract the lymph nodes at deer registration stations. In 2008, the DNR tested the lymph nodes of 500 hunter-harvested deer along the Wisconsin border from Houston County to St. Croix State Park. In 2009, the agency tested a total of 2,685 deer taken in southeastern Minnesota.

DNR has implemented its CWD response plan. The critical first step was to identify the number and current distribution of deer in the Pine Island area. This was done using an aerial survey. Now that this data is compiled, sampling to collect additional lymph nodes for testing has started. Working with landowners, shooting permits are being issued for landowners or their designees to take deer on their own property. Sharpshooting of deer with permission of cooperating landowners may occur to complete the necessary sample of 900 deer, 500 of which need to come from within roughly a five-mile radius of where the infected deer was harvested in Fall 2010. DNR also implemented a deer feeding ban in a four-county area of southeastern Minnesota, and is restricting carcass movements out of the area.

That's possible but it's premature to speculate. The only way to know if other deer have CWD is to continue doing surveillance. Collection of additional samples this winter will be done in a highly targeted way and only with permission of cooperating landowners.

Based on the fact that only one deer has tested positive for CWD among more than 500 samples, the rate of occurrence is likely low. Still, people with venison in their freezer from this area should know the following:

1. The National Center for Disease Control (CDC) and the World Health Organization (WHO) have found no scientific evidence that CWD is transferrable from animals to humans; and
2. The CDC advises against eating animals known to have CWD.

So, people with venison in their freezer that was harvested from this area will need to make decisions based on the information above. The Minnesota Department of Health – not the DNR – provides guidance to citizens on food consumption issues.

CWD causes a characteristic spongy degeneration of the brains of infected animals resulting in emaciation, abnormal behavior, loss of bodily functions and death. CWD belongs to a group of diseases known as transmissible spongiform encephalopathies (TSEs). Though many observers try to compare CWD with "mad cow disease", the diseases are distinctly different.

The disease agent is a prion, an abnormal form of cellular protein that is most commonly found in the central nervous system and in lymphoid tissue. The prion "infects" the host animal by promoting conversion of normal cellular protein to the abnormal form.

The origin of CWD is unknown, and it may never be possible to definitively determine how or when CWD arose. It was first recognized as a syndrome in captive mule deer held in wildlife research facilities in Colorado in the late 1960s, but it was not identified as a TSE until the 1970s. Computer modeling suggests the disease may have been present in free-ranging populations of mule deer for more than 40 years.

It is not known exactly how CWD is transmitted. The infectious agent may be passed in feces, urine or saliva. Transmission is thought to be lateral (from animal to animal). Although maternal transmission (from mother to fetus) may occur, it appears to be relatively unimportant in maintaining epidemics.

Because CWD infectious agents are extremely resistant in the environment, transmission may be both direct and indirect. Concentrating deer and elk in captivity or by artificial feeding probably increases the likelihood of both direct and indirect transmission between individuals. Contaminated pastures appear to have served as sources of infection in some CWD epidemics. The apparent persistence of the infectious agents in contaminated environments represents a significant obstacle to eradication of CWD from either captive or free-ranging cervid populations.

The movement of live animals is one of the greatest risk factors in spreading the disease into new areas. Natural movements of wild deer and elk contribute to the spread of the disease, and human-aided transportation of both captive and wild animals greatly exacerbates this risk factor.

CWD poses serious problems for wildlife managers, and the implications for free-ranging deer, elk and moose are significant:

• Ongoing surveillance programs are expensive and draw resources from other wildlife management needs;
• Impacts of CWD on population dynamics of deer and elk are presently unknown. Computer modeling suggests that CWD could substantially reduce infected cervid populations by lowering adult survival rates and destabilizing long-term population dynamics;
• Where it occurs, CWD may alter the management of wild deer and elk populations, and it has already begun to do so; and
• Ultimately, public and agency concerns and perceptions about human health risks associated with all TSE's may erode hunters' confidence and their willingness to hunt in areas where CWD occurs.