Is chronic wasting disease a threat to humans?

Areas with CWDChronic wasting disease (CWD) is a prion disease of cervids (deer, elk, moose). It was first detected in Wyoming and Colorado, and has since spread rapidly throughout North America (illustrated; image credit). Because prions that cause bovine spongiform encephalopathy (BSE, mad cow disease) are known to infect humans, there is concern that CWD might also cross the species barrier and cause a novel spongiform encephalopathy. Recent experimental results suggest that CWD prions are not likely to directly infect humans.

The prion protein PrPC is encoded by the prnp gene, which is essential for the pathogenesis of transmissible spongiform encephalopathies (TSEs). Transgenic mice have been used to understand the species barrier to prion transmission. When mice are inoculated with human prions, few animals develop disease and the incubation periods are over 500 days. When the mouse prnp gene is replaced with the human gene, the mice become uniformly susceptible to infection with human prions and the incubation period is shorter. The species barrier to prion transmission is therefore associated with differences in the prion protein sequence between host and target species.

Mice have been used to understand whether CWD prions might be transmitted to humans. Mice are not efficiently infected with CWD prions unless they are made transgenic for the cervid prnp gene. Four different research groups have found that  mice transgenic for the human prnp gene are not infected by CWD prions. These findings suggest that CWD prions are not likely to be transmitted directly to humans. However, changing four amino acids in human prnp to the cervid sequence allows efficient infection of transgenic mice with cervid prions.

Another concern is that prions of chronic wasting disease could be transmitted to cows grazing in pastures contaminated by cervids. Prions can be detected in deer saliva and feces, and contamination of grass could pass the agent on to cows. In the laboratory, brain homogenates from infected deer can transmit the disease to cows. Therefore it is possible that cervid prions could enter the human food chain through cows.

A further worry is that BSE prions shed by cows in pastures might infect cervids, which would then become a reservoir of the agent. BSE prions do not infect mice that are transgenic for the cervid prnp gene. However, intracerebral inoculation of deer with BSE prions causes neurological disease,  and the prions from these animals can infect mice that are transgenic for the cervid prnp gene. Therefore caution must be used when using transgenic mice to predict the abilities of prions to cross species barriers.

Although the risk of human infection with CWD prions appears to be low, hunters should not shoot or consume an elk or deer that is acting abnormally or appears to be sick, to avoid the brain and spinal cord when field dressing game, and not to consume brain, spinal cord, eyes, spleen, or lymph nodes. No case of transmission of chronic wasting disease prions to deer hunters has yet been reported.

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  • Ben Blumberg

    This is an outstanding discussion of an issue I hope we never have to deal with!

  • GaryChandler
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  • Wayne LaCour

    Just a point of information:…Why has several Universities Not found a cure…mad cow and this deer …I bet something real cheap could be made to stop it now…I know its not all simple but…when “science labs” begin with the giant stack of “gene” study….etc…which leads (like ABA BS) years and years and years of “study”…no cures..just study it more…like todays cancer $$$$ripoff AMA BS….Universities should be given guidelines…FIND A DAMN CURE AND CHEAP MEDS”””” ….PERIOD..STOP STUDY ON GENES…FIND SOMETHING IN NATURE THAT KILLS THIS DISEASE AND THE PRIONS…….DONE…

  • Old flintlock

    If you think it is so easy, why don’t you spend the 8-10 years in College necessary to obtain a terminal degree, do the research, “find something in nature that kills this disease” and get filthy rich. As a retired Microbiologist/ MD researcher I would be delighted at reading your findings and would be grateful if you would share your wisdom on how simple the whole process is. By the way, before you embark on your academic career, I suggest you first learn how to write a proper paragraph in English. It would go a long way in people taking you seriously

  • Beowulfsfriend

    Under the House tax plan, 10 years in college as a researcher will cost too much. Who needs science when god will fix everything in the end.

  • Beowulfsfriend

    Is it because it is the prions and not actually the virus which makes it impossible to cook and kill?

  • JosephD

    Yes. Since it is just a misfolded protein cooking does not destroy the infectious agent. If you get the meat up to a high enough temp to destroy the prions then the meat, also made of protein, is no longer meat.