Today I disposed of the elk meat my brother sent me from Wyoming this year. It tastes great, but I was scared. He got his elk near the Colorado border, and the elk and deer there seem to be infected with a disease alarmingly like mad cow disease.
Mad cow disease is not an infectious disease in the sense we are accustomed to dealing with. Unlike AIDS or flu or chicken pox, it is not introduced into your body by viruses, bacteria, or other microbes. Unlike cancer or muscular dystrophy or cystic fibrosis, it is not the result of a DNA defect. Individuals affected with mad cow disease have no microbial infection, and their DNA is normal.
Mad cow disease results instead from misfolded proteins called prions that pass to an affected person’s brain. At first, only a few proteins may be misfolded, and little harm to the brain results. But each misfolded protein induces other brain proteins to misfold in the same way, so that, spreading like a rumor, the mistake eventually becomes widespread. Sponge-like holes develop in the brain, which gradually loses the ability to function.
Mad cow disease is one of a family of prion-caused brain diseases called transmissible spongiform encephalopathies (that is, infectious hole-causing brain disorders), or T.S.E.’s.
Until the outbreak of mad cow disease in England in the mid-1980s, it was generally thought that each kind of animal had its own kind of T.S.E. Sheep had a form called scrapie, for example, and humans had Creutzfeldt-Jacob disease (CJD). Even hamsters have their particular form of T.S.E.
It took British officials quite a long time to come to grips with the problem, and a lot of British beef-eaters became infected. 77 have died, and it is thought that hundreds more will. The British eventually had to slaughter almost 4 million cattle to eliminate the disease-causing prion from their foodchain. Now, the appearance of the prion in 90 cows in France in recent weeks has led to a growing panic that the prion has not yet been banished from European diets.
What we learned from the outbreak of mad cow disease is that T.S.E.s can be transmitted from one species to another. Tests of British patients afflicted with mad cow disease point not to human CJD, but rather to the form of the prion found in sick British cows. Humans in Britain had become infected by eating hamburger containing brain or spinal cord tissue from infected cows.
Biologists are now looking more closely at cross-species transmission of T.S.E.s. The results are not encouraging. It appears sheep prions can infect cows. Earlier this year researchers demonstrated that prions from hamsters infect mice just fine, and that blood or nervous tissue from such infected mice carries the disease to other mice. It seems
increasingly clear that prions can pass readily from one species to another.
So what has this got to do with my brother’s elk meat? A sickness called “chronic wasting disease” has been reported for several years among the deer and elk populations living along the border shared by Colorado and Wyoming. As my luck would have it, this is just where my brother bagged his elk. Wildlife biologists estimate that in these populations, chronic wasting disease affects 1 percent of elk and from 6 to 15 percent of deer.
Chronic wasting disease is a T.S.E. It is caused by a prion. No traces of human disease have been traced to elk or deer meat, but the available scientific evidence suggests that transmission is probably possible. In laboratory experiments carried out in test tubes, elk and deer prions from chronic wasting disease animals were able to convert healthy human prions into infectious prions. There was no clear demonstration that these test-tube-converted prions would actually produce a brain disease in humans, but the presumption seems strong.
Most Colorado and Wyoming hunters are not aware of the problem, although biologists are trying to get their attention. Because T.S.E.s typically take ten years or more to produce symptoms, it may be quite a while before hunters get clear evidence of the dangers presented by prion-infected elk and deer.
In the meantime, while the scientists explore the potential problem, it seems to me prudent to be cautious. Would you eat a hamburger from a cow in a herd where 15% of the herd had mad cow disease?
A lot of my friends in Missouri hunt deer. Should they worry? I am not aware of any instance of chronic wasting disease among Missouri deer. People have been eating deer meat in our state for hundreds of years with no evidence of ill effects. While I would love to see a serious screening of Missouri deer herds for T.S.E.s, I see no reason to panic over the remote possibility of “mad deer disease” here in Missouri. On the other hand, don’t bother to offer me any deer meat this year.
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