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Culling Out The Infirm

Illinois program to curtail CWD in deer herd deemed a success

Culling Out The Infirm
Illinois program to curtail CWD in deer herd deemed a success

For more than 10 years, Illinois wildlife officials have culled whitetail deer suspected of having or coming in contact with chronic wasting disease in an effort to curtail the deadly disease.

Now a study by researchers at the University of Illinois suggests that not only is the practice helping to keep CWD from spreading, but the deer population in the state is also continuing to grow.

“The culling was designed to curtail the spread of the disease while at the same time keeping the hunters with a good, strong (herd),” said Jan Novakofski, a professor of animal sciences at the University of Illinois and one of the authors of the study. “We’ve found that the prevalence of CWD has remained flat for 10 years, and the practice (of culling) should be considered a success.”

Other authors of the study are Nohra Mateus-Pinilla, a wildlife veterinary epidemiologist at the INHS, and postdoctoral researchers Mary Beth Manjerovic and Michelle Green.

Each year the Illinois Department of Natural Resources tests 7,000 deer that were hunted, culled or incidentally killed for CWD infection. Then, usually in winter, the IDNR sends in sharpshooters at sites where the disease has been found. Most of the herd reduction occurs on private lands where the state has received permission.

Last year, sharpshooters culled about 600 deer in Illinois.

“We know a lot about how far deer typically move,” Novakofski said in a university release. “If they’re sick, they’re going to spread the disease that far. So if you find a deer that’s sick, you draw that circle and you shoot there.

“(It’s) a textbook scientific strategy for control. You reduce contact and you reduce the spread of infection with the smallest overall impact on healthy deer.”

Work with the Illinois Natural History Survey, which is part of the Prairie Research Institute at the university, has shown that the strategy has worked. The prevalence of CWD in tested Illinois deer has remained at about 1 percent from 2002, when the culling practice began, through last year.

CWD, which is similar to mad cow disease, can take years to develop but is always fatal. It was first discovered in captive mule deer in Wyoming in the 1960s and was first found in the wild in 1981. The disease has been found in deer, elk and moose. It has not been linked to human disease, but the Centers for Disease Control recommends not eating the meat from CWD-positive animals.

The study maintains that, despite the culling, deer populations in those regions typically thrived.According to the university release, 147,830 deer were killed in Illinois in 2001 – before the appearance of CWD – and 181,451 were taken in 2012.

“We wanted to know whether Illinois hunters have fewer deer to hunt now than they did before CWD (arrived),” Mateus-Pinilla said. “We found that hunter harvest has increased, and the prevalence of CWD has been maintained at low levels for 10 years in Illinois.”


Of the 10 Illinois counties where cases of CWD have been discovered, two saw a reduction of deer taken by hunters between 2001 and 2012. Those reductions were 11 to 20 percent.

The team of researchers compared Illinois’ CWD management strategy with that of Wisconsin, where CWD was also discovered in 2002. When Wisconsin abandoned aggressive control measures — including sharpshooting and longer hunting seasons — to control CWD, prevalence rates have increased to about 5 percent across the disease management area since 2007.

“We can’t find an environmental or other variable that explains the increase in prevalence except a change in management,” Novakofski said.

Novaofski said further studies on CWD and deer management would likely involve the connection between the disease and deer reproduction and genetics. Meanwhile, he said he believes culling as a management strategy is a good policy for the future.“I look at it as a bit like insurance,” he said. “CWD is a disease that is going to be very, very difficult to eradicate – if you can at all. In the meantime, I look at it a bit like insurance. If you can keep it at a reasonable level, it’s insurance for the future.”

The study, titled “The Importance of Localized Culling in Stabilizing Chronic Wasting Disease Prevalence in White-Tailed Deer Populations,” appears in the Sept. 25 edition of Preventive Veterinary Medicine and can be found online at

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