Chronic Wasting Disease in Deer

A deadly disease of Wisconsin white-tailed deer has appeared in Wisconsin. You may have read about it in the paper and heard about it on the news. It's called chronic wasting disease (CWD) and it was discovered in February of 2002 in Wisconsin's wild deer herd. This disease, which is found in some states west of the Mississippi River, somehow crossed two states,"jumped" the river and made it to Wisconsin.

What is Chronic Wasting Disease?

CWD is a deadly disease found in North American deer and elk. It was first discovered in 1967 when it infected mule deer in a wildlife research facility in northern Colorado. No one knew at the time exactly what it was. It wasn't until 1978 that the disease was identified as a transmissible spongiform encephalopathy (TSE). The spongiform encephalopathy diseases basically cause holes in the brain, giving the brain a "spongelike" look. That's where the word spongiform in the name comes from. Other TSE diseases include "mad cow" disease in cattle, scrapie in sheep, and Creutzfeldt-Jakob disease (CJD) in humans.

Chronic wasting disease can affect a number of different species including elk, mule deer, white-tailed deer and black-tailed deer. It is spread by close contact with an infected animal or by being exposed to an area contaminated with the disease. How exactly the disease spread to Wisconsin from the Western states is a mystery.

How does CWD affect deer?

Months to years can pass before an animal infected with CWD begins to show symptoms of the disease. Chronic wasting disease is a slowly progressive disease where the animal "wastes" away. Symptoms of the disease are not usually seen until an animal is 18 months or older. An infected animal will eventually begin to show symptoms of the disease including weight loss, tremors, stumbling, unusual behavior, increased salivation, difficulty swallowing and excessive thirst or urination.

Chronic wasting disease is a fatal disease that affects the central nervous system of the infected animal. Research has shown that a protein known as a prion (PREE-on) causes the disease. A prion is an abnormally shaped form of a normal cellular protein. An animal becomes infected with the disease when prions present in the tissue stimulate normal cell proteins to become abnormal forms. Scientists think that the prions only accumulate in certain parts of the body, including the brain, lymph nodes, eyes, spinal cord, tonsils and spleen.

Because the prions haven't been shown to collect in muscle tissue, the risk of eating the meat of an infected animal is still debated. The World Health Organization has recommended not eating meat from an animal that may be infected, yet there is no scientific evidence that chronic wasting disease can affect humans.

Where is the disease found?

In the mid-1970s, chronic wasting disease traveled to Canada in infected mule deer brought from a park in Colorado. Now the disease infects deer and elk on 39 game ranches in Saskatchewan and Alberta.

By the mid-1980s, the disease had spread from captive-farmed herds to free ranging wild deer and elk in the northeastern part of Colorado and southeastern Wyoming. In 1997, chronic wasting disease was found in a farmed herd in South Dakota. Since then, additional infected herds have been found in South Dakota, Nebraska, Oklahoma, Montana, Kansas, Minnesota and Colorado.

In the spring of 2001, chronic wasting disease was discovered in free-ranging deer in the southwestern corner of Nebraska and also in two wild mule deer in Saskatchewan. These were the first cases ever discovered in wild Canadian animals.

The first incidence of chronic wasting disease in wild deer east of the Mississippi River was the discovery of the disease in Wisconsin. In late February 2002, the disease was found in samples from deer registered in Mt. Horeb during the previous fall hunting season. A sampling of wild deer in the spring of 2002 in the Mt. Horeb area revealed 18 more cases of the disease. Since then, sampling has turned up wild deer infected with the disease in Dane, Iowa, Richland, Sauk, Walworth and Rock counties. Infected deer have also been found in Illinois along the Wisconsin border by Walworth and Rock counties. This past year one deer tested in Kenosha county turned up positive. Sixteen cases of Chronic Wasting Disease have also been found in captive deer on some of the game farms in Wisconsin.

What's being done to stop the disease?

Steps are being taken to slow down or, hopefully, get rid of the disease in Wisconsin by drastically reducing the number of deer in the infected areas.

In the fall of 2002, the DNR collected deer from every county in the state during the deer hunting season. These deer were tested for Chronic Wasting Disease. Since then the department has continued to test for the disease. There will be more testing this fall and winter but mostly in and around the areas where we know the disease occurs. This will help keep track of the disease and find out whether it is spreading.

Everyone needs to work together to try to control this disease in Wisconsin. In order to halt the spread of CWD, residents of Wisconsin are being asked to keep hunting and to watch for abnormal behaviors in local deer and report it to the DNR.

As the work on CWD continues, we'll keep you posted on testing results and what's being done to try to stop the spread of this deadly deer disease. You can read more about this disease and Wisconsin's efforts to test deer by going to the Department of Natural Resources Chronic Wasting Disease page.