For now, more questions than answers with CWD

September 25, 2002 Capital Times (Madison, WI) by Tim Eisele
There are few guarantees in life. Chronic wasting disease (CWD) is a good example.

According to the World Health Organization, there is no evidence that CWD passes to human beings.

The Wisconsin Department of Agriculture, Trade and Consumer Protection-Food Safety Division says prions -- the carriers of the disease -- concentrate where there is a lot of nerve tissue, such as the brain, spinal cord and eyes, and in lymph nodes and the spleen. Prions haven't been found in meat (muscle tissue), the Food Safety Division states. Still, many hunters, and just about every cook preparing dinner for the family, wants to know unequivocally their venison is 100 percent safe to eat.

Currently, there are no such guarantees.

The best information will be available to hunters following sample testing this fall.

The Department of Natural Resources (DNR) will sample 500 deer in every county in order to determine, with about 99 percent certainty, whether or not CWD is present in the herd in that area.

The best food safety test will be if the sampling shows CWD is not present in deer in the remainder of the state. If this is the case, it should give those who enjoy eating venison from those areas a sense of relief.

If, however, more CWD is found in the wild herd, it will expand the uncertainty now involving the CWD eradication zone near Mount Horeb.

Currently, only one test is considered valid -- immuno histochemical staining (IHC). This is considered the "gold standard," and is conducted on deer shot within the CWD eradication zone -- plus on 500 deer from each county. It involves taking a sample from the brain of each animal, mounting the sample on a slide and staining it to destroy normal prions. Abnormal prions are left, which scientists can see using a microscope.

But Judd Aiken, a professor of animal health and biomedical sciences at the University of Wisconsin, said there is no test that can say with 100 percent certainty that an animal does not have CWD.

"The tests we have pick up the infection at some point during the disease," said Aiken, who has studied prions for 17 years. "If we get a positive, it definitely is infected. But at the early stages of the disease, with the tests we have now, it's not detectable."

This raises questions of whether an animal, shot by a hunter, could be infected by CWD withoug testing positive.

Aiken underscored the seriousness of the disease.

"CWD is 100 percent fatal - there is no cure and no treatment," he said.

DNR veterinarian Julie Langenberg said a waiting period is needed for all tests - both the IHC and a newer experimental quick-test which will be tested this fall in Wisconsin and a few other states.

"The most frustrating core information that we need to get across to citizens is that these are diagnostic tests designed to tell us if the animal is positive or not positive. But not positive does not mean that it is negative for (abnormal) prions," Langenberg said. "Not positive for the abnormal prions means that within the limitations of these tests, whether it's the standard test or the newer rapid tests, we couldn't detect that it was positive."

Langenberg said there are a number of reasons why an animal with CWD would not test positive. One is that it is too early in the disease and can't be detected in the tissues.

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