Report 3 of the Council on Scientific Affairs (A-05)

Chronic Wasting Disease:  Implications for Human Health

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Summary

Objectives. To summarize the scientific literature on the risks to human health due to chronic wasting disease (CWD) in deer and elk, highlight the regulations protecting humans from transmission of CWD, and present recommendations.

Data Sources. Literature searches were conducted in the PUBMED database for English-language articles published between 1980 and 2005 using the search term chronic wasting disease. The Lexis/Nexis news databases were searched with the search term chronic wasting disease AND human health.The World Wide Web was searched, using the “Google” search engine, with the search term chronic wasting disease AND human health.

Results. Evidence is lacking that CWD can be transmitted to the human population.  Epidemiologic investigations of several potential cases have shown that these were either familial human transmissible spongiform encephalopathies (TSEs) (eg, Gerstmann-Straussler Scheinker [GSS] syndrome), or sporadic cases of Creutzfeldt-Jakob disease (CJD).  The only 2 known cases of human TSE positively associated with a history of exposure to deer or elk meat from a CWD-endemic area both proved to be cases of sporadic CJD.  Additionally, laboratory studies suggest an inefficient conversion of normal, protease-sensitive human prions into abnormal, protease-resistant human prions by the CWD prion, implying a substantial species barrier.  These laboratory studies also support the conclusion that transmission of CWD to humans is unlikely.  Significant measures are already in place to prevent the potential exposure of humans to CWD, both direct and indirect.  The Food and Drug Administration currently has a feed ban in place that prohibits the use of materials from any deer or elk for feeding ruminant animals, and in 2003 issued a guidance that prohibits the use of CWD-positive material in animal feed.  Additionally, the ban prohibiting high-risk material from cattle from entering the human food chain will serve to indirectly protect humans from CWD that may have passaged through domestic cattle.  Furthermore, the U.S. Department of Agriculture (USDA) and the Agricultural Research Service have dedicated significant resources to CWD research, control, and eradication.  The USDA is working with state governments and Native American tribes to support surveillance and management of CWD in free-ranging deer and elk.  Many states have also provided guidance to hunters on how to reduce their exposure to potentially CWD-infected animals.

Conclusions. The risk of CWD transmission to the human population appears very low.  Appropriate measures are in place to protect the human population from CWD.  However, as indicated in Council on Scientific Affairs Report 6 (A-98), adherence to guidances and enforcement of regulations are critical for the protection of the human population.  While the risk may be very low, the potential still exists that CWD may either transmit to humans inefficiently, or may play a role in enhancing the onset of CJD in humans who are already genetically vulnerable to developing that disease.  The experience with bovine spongiform encephalopathy (BSE) also suggests that with sufficient exposure over time, the species barrier alone is insufficient to protect humans from animal prion diseases.  As such, while unlikely, it is possible that human exposure to CWD has simply been insufficient to cause transmission of disease to humans.  Accordingly, it is important that surveillance efforts on the incidence of CJD in humans continue, not just to identify possible transmission of CWD, but also for BSE.  Continued efforts to control and/or eradicate CWD are justified.  Continued research, both epidemiologic and laboratory-based, into the potential that CWD may transmit to humans should be encouraged.

RECOMMENDATIONS

The following statements, recommended by the  Council on Scientific Affairs, were adopted by the AMA House of Delegates as AMA policy and directives at the 2005 AMA Annual Meeting:

The AMA:

1. Reaffirms Policy H-150.959 (3), (5), and (6): Risk of Transmission of Bovine Spongiform Encephalopathy to Humans in the United States, and Policy H-150.950, Regulation of Meat Plants That Process Wild Game (AMA Policy Database). (Reaffirm Policy)
2. Urges the Food and Drug Administration (FDA) to: (1) continue aggressive enforcement of existing regulations to prevent the transmission of animal-transmissible spongiform encephalopathies to humans; and (2) consider making Draft Guidance Document 158, Use of Material From Deer and Elk in Animal Feed, into a regulation. (Directive)
3. Encourages continued research into the potential transmission of chronic wasting disease (CWD) to other animals and humans. (Directive)
4. Supports continued surveillance of the CWD epidemic in cervids and continued investigation into human cases of CJD that appear to have an epidemiological link to exposure to CWD. (Directive)

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