By Douglas R. Dufford
District Wildlife Biologist, Illinois Department of Natural Resources
Chronic wasting disease (CWD) is a fatal disease of deer, elk and moose. It does not appear to be a human health threat, though disease experts caution against eating venison from deer known to be infected.
First observed in the 1960s in captive deer in Colorado, CWD is now a very real and serious threat to wild deer throughout North America. During the past 15 years, the known range of the disease has increased dramatically (at least 17 states and two Canadian provinces have now documented CWD), and the rate of CWD infection appears to be increasing throughout much of that range.
One of the most dramatic examples of the potential of CWD comes from southeastern Wyoming, where more than 50 percent of tested mule deer in the South Converse Hunting Unit (1,224 square miles) had CWD during the 2011 hunting season, compared to only 15 percent in 2001.
Unfortunately, CWD is present in northern Illinois. The first case was found in a white-tailed deer near Roscoe, Ill., in 2002. Through June 30, 2012, the Illinois Department of Natural Resources (IDNR) tested more than 65,000 deer statewide and identified 372 individual deer infected with CWD. These were in 10 northern Illinois counties — Boone, Winnebago, DeKalb, McHenry, Kane, Grundy, LaSalle, Ogle, Stephenson and Jo Daviess. The highest concentration of CWD cases have been found along the Boone-Winnebago county line from Wisconsin down into northwestern DeKalb County.
Shortly after the first case was discovered, the IDNR implemented a CWD Management Program. The goals are to suppress CWD prevalence rates so they remain low, and to slow the rate of spread to the remainder of the state by reducing deer densities in CWD infection areas and maintaining deer herds at lower levels. Lower densities and the removal of CWD-positive deer reduce contact rates between sick and susceptible individuals.
Deer densities are managed at the county level in the CWD area through liberal hunting regulations, including virtually unlimited numbers of firearm deer permits and the addition of a special CWD deer hunting season. Where needed, IDNR supplements hunter harvest with agency sharpshooting performed after the hunting seasons to allow for a focused removal of deer from specific areas where the disease is known to occur.
All sharpshooting is performed with landowner permission only in areas where it is safe to do so; all deer are retrieved and tested; and all venison appropriate for human consumption is donated to the Northern Illinois Food Bank for distribution to northern Illinoisans in need of food assistance.
In 2011-2012, results were obtained from 8,175 deer tested statewide for CWD. Fortunately, only 36 deer in seven counties were found to be CWD-positive. The highest number of positives was found in Kane County (seven), followed by Boone (five), DeKalb (five), Grundy (five),
McHenry (three), Ogle (two) and Stephenson (two). Most tested samples were from hunter-harvested deer (6,726 samples — 82 percent of the total), but sharpshooting accounted for most of the sick deer identified (25 positives, 69 percent of the total). Most positive deer were found in areas already known to have CWD, although expansion into eastern Grundy County was noted.
While most other states and provinces affected by CWD have experienced outbreaks that continue to worsen, infection rates in Illinois have remained relatively stable at low levels, averaging just below 1 percent for the 10 counties where CWD is known to occur.
CWD is distributed in a very patchy pattern in northern Illinois, and there are “hot spots” with much higher infection rates than other areas. Highest infection rates during 2011-2012 were found along the Boone-Winnebago county line from Wisconsin south to northwestern DeKalb County. Of interest is a pattern of decreasing infection rates observed in each of the last three years in the northern part of that area (north and northeast of Rockford), where infection rates declined to 5.4 percent this year. This is the area where the disease was first observed, and which historically has had the highest infection rates.
However, in the southern portions of this band, infection rates have remained steady or have been increasing, reaching Illinois’ highest rate of 12.4 percent in NW DeKalb and NE Ogle counties this past year. This pattern may be the result of differences in our ability to implement the CWD Management Program — landowner cooperation and support is very high in the northern area, but cooperators are much fewer in the south. Concerned, cooperating landowners are the key to disease management, and in the absence of that, disease control efforts cannot be successful.
Illinois’ program of CWD surveillance and active management during the past 10 years has successfully suppressed the rate of disease at very low levels. There is much work left to be done, however, and state budgets are very tight. There is strong evidence from around North America that when left unmanaged, CWD will increase and expand, with potentially devastating consequences for deer populations in the long term.
White-tailed deer are one of our most revered natural resources, and I’d like to think that Illinoisans will do everything in their power to protect that resource. I believe the future of white-tailed deer in all of Illinois lies in the hands of landowners and sportsmen in our CWD-positive areas.
More information is available at the IDNR website (http://dnr.state.il.us/cwd/) or by contacting me at (815) 535-2875.
From the Nov. 7-13, 2012, issue