Photo courtesy of the Illinois Department of Natural Resources.

November 1, 2022

Year 21 of Managing Chronic Wasting Disease in Illinois

A map of the counties of northern Illinois with navy, red, and gray tiny squares. The red indicates chronic wasting disease range in 2022. The red indicates chronic wasting disease range in 2003 to 2021. The gray indicates a municipality.
Distribution of all known CWD-infected deer identified in Illinois through June 30, 2022.

As the days get shorter and the temperatures cooler, the wildlife management professionals of the Illinois Department of Natural Resources (IDNR) find ourselves preparing for our 21st consecutive season of Chronic Wasting Disease (CWD) management. The CWD management and surveillance program started in 2002 when a female white-tailed deer was diagnosed with the disease in Boone County. CWD is an always-fatal neurological disease that affects animals in the Cervidae family. Animals in this family, also known as cervids, include deer, elk, moose and caribou. CWD can be passed directly from deer-to-deer or be contracted indirectly through a contaminated environment. The approach we use to manage the disease consists of two elements: surveillance and management.

Surveillance is accomplished by sampling wild white-tailed deer for CWD and associating that sample to the square mile section of Illinois from which the deer was taken. The majority of our CWD samples come from hunter-harvested deer, but other sources include sharpshooting, roadkill and suspect deer. The tissues collected for CWD testing are a pair of lymph nodes, which are sent to one of two labs for initial testing, and if positive, subsequent confirmatory testing. During the project period of July 1, 2021 to June 30, 2022, the IDNR sampled 9,886 deer for CWD. Well over 150,000 samples have been collected since surveillance started in 2002. Locations of CWD-positive deer are mapped, and the IDNR wildlife biologists conduct helicopter flights to determine deer distribution and population size within known CWD areas. This information enables staff to focus management activities on deer in winter concentration areas that included, or were near, CWD-infected properties.

Two gray, white-tailed deer forage for food by digging through the snow to reach vegetation underneath. The two deer are eating from the same spot in the snow. In the foreground is the text "Click here for more information on Chronic Wasting Disease in  Illinois."
Photo courtesy of the Illinois Department of Natural Resources.

CWD management (sharpshooting) begins after the Archery and Special CWD seasons wrap up in mid-January and generally occurs within two miles of where known CWD-positive deer were removed from the landscape. Management using sharpshooting to supplement hunter harvest allows IDNR to conduct localized, focused deer reductions in small areas known to have CWD. Our goals are to 1) reduce disease transmission rates by lowering densities in infected areas, 2) reduce environmental contamination from infected deer, and 3) remove sick deer from the population at a higher rate than deer are becoming newly infected. Advantages of sharpshooting include: 1) reductions are limited to areas with disease, so healthy populations in uninfected areas are not impacted as would be the case if hunting was the only management tool; 2) sharpshooting can be conducted on properties that do not normally allow hunting (or allow only very limited hunting), so management can occur in areas that normally serve as refuges to hunting; 3) focused sharpshooting has been shown to remove sick animals at a higher rate than hunting programs; and 4) sharpshooting can target specific high-risk deer social groups known to have CWD.

A map of northern Illinois counties with areas in yellow indicating chronic wasting disease management area boundaries across northern Illinois, winter 2022.
CWD management area boundaries across northern Illinois, winter 2022.

Our 20-year history of CWD sharpshooting wild deer means we have actively been managing the disease through targeted removals longer than any other wildlife management agency. But the program has not been without its challenges. For the first 16 years of the program, our apparent CWD prevalence rates in hunter-harvested adult deer were around or below 1 percent across all of our CWD counties. The past four seasons, however, we have observed a relatively rapid increase in prevalence rates; our statewide apparent prevalence was approximately 4.5 percent last season. We have also observed a significant increase in the total number of CWD-positive deer that have been identified each management season. The 2021-2022 total of 218 positives marks the third record high in the last four years. Additionally, we are now fighting Chronic Wasting Disease on a much larger geographic scale than we were in 2002, when we were limited to northern Illinois. CWD has now been confirmed in 19 counties. We have also been tracking a CWD outbreak in southeastern Missouri since Fiscal Year 2019. CWD-positive deer have been found in Missouri within mere miles of Kaskaskia Island, a portion of Illinois that lies west of the Mississippi River and is accessible only through Missouri.

A graphic features a close-up image of a profile of an adult male white-tailed deer. To the left of the photo is the text, "Please note, the firearm check station for McHenry County has moved to Volo Bog State Natural Area. For mandatory CWD check station hours and locations, please visit: ."
Photo courtesy of the Illinois Department of Natural Resources.

Despite the difficulties have we faced over the years, IDNR has been able to adapt to, and overcome, many of the challenges we have encountered. Technological updates allow our sharpshooters to more efficiently conduct targeted removals of deer in a variety of weather and light conditions. Upgrades, such as rubber tracks on our utility terrain vehicles, mean we can be more effective in muddy and snowy conditions while increasing the safety of our field staff. Interactive mapping programs allow the public to better visualize the known spread of the disease, and changes in the last two years to our testing procedure allow hunters to see quickly receive CWD test results—sometimes in as little as a few days, compared to weeks or even months prior to 2020. While CWD has continued to spread over the years in Illinois, our management actions have undoubtedly slowed the movement of the disease and mitigated its impacts in the counties where it is found.

A table with the years 2003 to 2022 across the top and Illinois counties down the left side. Numbers in the table indicate the number of chronic wasting disease-positive deer collected by county and fiscal year across northern Illinois.
Number of CWD-positive deer collected by county and fiscal year across northern Illinois, November 2002 through June 2022.

An undertaking of this magnitude, and one that has gone on for so long, cannot be done alone. First and foremost, I want to acknowledge the hard work and countless hours that have been contributed, over the years, by the members of the IDNR Division of Wildlife Resources. Additionally, we have received invaluable assistance from the IDNR Divisions of Fisheries, Forestry, Natural Heritage and Private Lands, along with the Illinois Nature Preserves Commission and the United State Department of Agriculture’s APHIS Wildlife Services Illinois program. Finally, we owe a “thank you” to the hunters who participate in our CWD surveillance program and the cooperating landowners who allow access to private property for CWD management. Without these conservation-minded individuals, CWD management in Illinois would be impossible.

Dan Skinner is the Forest Wildlife Program Manager with the Illinois Department of Natural Resources’ Division of Wildlife Resources.

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