Medical Society Of Milwaukee County
Position Statement
On Chronic Wasting Disease

Background

The recent introduction of Chronic Wasting Disease (CWD) into the deer population in Wisconsin has raised a variety of new issues for our state. As representatives of the Medical Society of Milwaukee County Public Health Committee we have recently reviewed the available literature on this issue and sought the advice of experts on prion diseases, such as CWD. Prions are the causative agents of transmissible spongiform encephalopathies (TSE) of both humans and animals.

Prions are believed to be mutant protein structures of a normal molecule produced in neurons of all mammals, including humans. These proteins have the unique property of converting normal molecules into new mutants. In this way, mutant prions can behave like infectious agents converting normally produced prion proteins in the brain into disease causing mutant molecules. In contrast to traditional infectious agents, these small protein fragments are highly resistant to heat, radiation and chemical disinfectants. In addition, unlike many other proteins, mutant prions are also highly resistant to proteases (usual method of destroying this class of molecules). As a result, prions can remain "infectious" despite “normal” sterilization techniques. Prions thus pose unusual public health challenges.

To understand the basis for recent concern, a review of the events of the 1990's with another animal prion disease has been helpful. In 1986 scientists first described bovine spongiform encephalopathy (BSE) or "mad cow disease". Within a decade this became an epidemic among British cattle, fueled by feeding cows the waste remains of dead animals as a protein supplement. This ultimately resulted in the destruction of much of the British herd by high temperature incineration. For five years, the public health community raised concerns in England about the potential transmission of BSE to humans. Finally the first cases of new variant Creutzfeldt-Jakob disease (CJD) was identified in young adults in Britain. Extensive investigation of the now 100+ cases strongly suggest that this fatal condition is human BSE, likely acquired by eating contaminated beef. Of specific concern was the use of bovine offal (brains, spinalcord, eyes and lymphatic tissue) as fillers in "fast food hamburgers" and processed meat. Use of these beef byproducts (offal) is now outlawed, for human consumption, in Britain and all of Europe.

Not all parts of a cow with BSE are highly “infectious”. Most of the mutant prions are concentrated in the offal. As a result, beef is now handled differently in all of Europe. Specific procedures are mandated to avoid contamination of meat by potentially mutant prions. These include using separate saws to remove the head and spinalcord and entirely different equipment to cut up and process the meat. Unused parts of the cow have specific disposal procedures and equipment used for processing beef is not used for processing meat from other species of animals. These extra measures were put in place to significantly reduce the risk to humans should a BSE cow get through the stringent pre-processing screening procedures.

Current scientific knowledge does not allow us to definitively predict whether CWD of deer will behave like BSE or like scrapie, a prion disease of sheep. Despite the century old practice of eating sheep brains by certain ethnic groups scrapie does not appear to make the species jump from sheep to man. On the reassuring side, there is currently no convincing data that a human has contracted CWD. On the concerning side, are studies dating back to 1986 which suggest an association between CJD and hunting, handling or eating wild animals (including deer). Since 1996, four cases of CJD have been identified by the CDC in patients under 30. These were investigated and three had a significant history of venison ingestion. Although this study concluded " no strong evidence for a causal link", this conclusion was based, in part, on the hypothesis that human CWD would look like human BSE and partly because each case had a different genetic profile with respect to their prion genes. In England, it took over twenty cases for scientists to definitively determine that transmission had occurred. Additional “clusters” of CWD cases are still under investigation. Finally, it should be recognized that human exposure ten years ago (projected minimum incubation period) was extremely low, given the rare nature of CWD in 1993 and its restriction to a small area in NE Colorado. Thus the lack of confirmed human cases does not mean that transmission is not possible.

Recent in vitro studies performed by Caughey et al suggest that deer prions from CWD can convert, at a low level, human prions into “infectious” mutants in vitro. If this is the case in vivo, then at least a small risk of acquiring CWD should be anticipated from ingesting the brains or lymphatic tissue of a deer with CWD. For these reasons, the Wisconsin Department of Agriculture, Trade, and Consumer Protection (Food Safety Division) has already recommended not eating deer offal and not eating any part of a deer that appears ill.

MSMC position

In light of these known facts and the potential, and currently unknown, risk to humans, the Public Health Committee of the Medical Society of Milwaukee County recommends that at a minimum, the State of Wisconsin should consider taking the same public health precautions that the English imposed on the British beef industry, on the currently unregulated "custom processing industry" of deer carcasses. Regulation would also enhance appropriate disposal of many deer carcasses. Deer offal (brains, spinalcord, eyes and lymphatic tissue) should also be excluded from all “deer sausage” and banned for human consumption. In addition, some concern should be raised over the practice of granting exemptions to licensed beef processors to periodically process venison. Deer prions could survive standard cleaning procedures imposing a potential risk to the beef, pork and chicken subsequently processed.

Approved by the MSMC Board of Directors – October 1, 2002

References
Brown P., Will R., Bradley R., Asher D., Detwiler L, (2001, January-February) Bovine Spongiform Encephalopathy and Variant Creutzfeldt-Jakob Disease: Background, Evolution and Current Concerns. Emerging Infectious Diseases, Vol. 7, No. 1, 6-16

Olds, G. Richard, MD, (1998, June). Kuru and Mad Cow Disease: Understanding the Prion Theory. Cleveland Clinic Journal of Medicine, Vol. 65, No. 6, 291-296

Caughey, Bryon, (2000, July) Transmissible spongiform encephalopathies, amyloidoses and yeast prions: Common treads? Nature Medicine, Vol. 6, No. 7, 751-754

Caughey, Bryon, (2001, April) Interactions between prion protein isoforms: the kiss of death? Trends in Biochemical Sciences, Vol. 26, No. 4, 235-242

Purdey, M., (2002) Ecosystems supporting clusters of sporadic TSEs demonstrate excesses of the radical-generating divalent cation manganese and deficiencies of antioxidant co factors Cu, Se, Fe Zn, Does a foreign cation substitution at prion protein’s CU domain initiate TSE? Medical Hypotheses, Vol. 54, No. 2, 278-306

Race, R., Raines, A., Raymond G., Caughey, B., Chesebro, B, (2001, November) Long-term Subclinical Carrier State Precedes Scrapie Replication and Adaptation in a Resistant Species: Analogies to Bovine Spongiform Encephalopathy and Variant Creuzfeldt-Jakob Disease in Humans. Journal of Virology, Vol. 75, No. 21, 10106-10112

Brown, P., Cathala, F., Castaigne P., Gajdusek, D., (1986, November) Creutzfeldt-Jakob Disease: Clinical Analysis of a Consecutive Series of 230 Neuropathologically Verified Cases. Annals of Neurology, Vol. 20, No. 5, 597-602

Davanipour, Z., Alter, M., Sobel, E., Asher, D., Gajdusek, D. (1986) Transmissible Virus Dementia: Evaluation of a Zoonotic Hypothesis. Neuroepidemology 5: 194-206

Raymond, G., Bossers, A., Raymond L., O’Rourke, K., McHolland L., Bryant III, P., Miller, M., Williams, E., Smits, M., Caughey, B. (2000) Evidence of a molecular barrier limiting susceptibility of humans, cattle and sheep to chronic wasting disease. EMBO Journal, Vol. 19, No. 17, 4425-4430

Wisconsin Department of Agriculture, Trade and Consumer Protection, Food Safety Division. Common Sense Precautions for Handling and Processing Deer. (608) 224-5130.