Can chronic wasting disease (CWD) in deer be transmitted to humans?

Chronic Wasting Disease and Human Transmission Risk

There is currently no confirmed evidence that chronic wasting disease (CWD) from deer can be transmitted to humans, but the potential risk cannot be entirely excluded and warrants continued caution regarding consumption of CWD-infected cervid meat. 1, 2

Current Evidence on Human Transmission

Laboratory Studies Show Strong Species Barrier

• Cynomolgus macaques (a primate model closely related to humans) showed no evidence of CWD transmission after 13 years of observation following both intracerebral and oral inoculation with high-titer CWD-infected deer and elk brain tissue. 1
• These macaques were monitored using highly sensitive prion detection assays (RT-QuIC, immunohistochemistry, immunoblotting) with no clinical, pathological, or biochemical evidence of prion infection. 1
• This contrasts sharply with squirrel monkeys, which were highly susceptible to CWD infection in the same experimental conditions, suggesting significant species-specific barriers exist. 1

Epidemiological Surveillance Findings

• A six-year longitudinal follow-up study of 81 individuals exposed to CWD-contaminated venison at a 2005 sportsmen's feast in New York found no emergence of prion disease or unusual neurological conditions. 3
• No epidemiological studies to date have confirmed CWD transmission to humans in areas where the disease is endemic and cervid consumption is common. 1, 2

Critical Caveats and Ongoing Concerns

The Prion Incubation Period Problem

• Prion diseases can incubate for multiple decades before clinical symptoms manifest, meaning current negative epidemiological data does not definitively rule out future human cases. 3
• The variant Creutzfeldt-Jakob disease (vCJD) outbreak from bovine spongiform encephalopathy (BSE) demonstrates that cross-species prion transmission to humans is possible, making vigilance essential. 2, 4

Potential Exposure Pathways

• If CWD were transmissible to humans, approximately 11,000 mouse intracerebral log ID50 units of infectivity could enter the human food chain from a single CWD-positive red deer through either commercial processing or field dressing. 5
• In commercial abattoirs, approximately 13% of total carcass infectivity would reach the food chain, while 87% becomes animal by-product material. 5
• For field-dressed wild deer, approximately 13% goes to the food chain and 85% is buried in the environment. 5

Geographic Spread and Prevalence

• CWD has been detected in 25 U.S. states, 2 Canadian provinces, South Korea, Norway, and Finland as of 2018. 1, 2
• The disease affects deer, elk, moose, and reindeer with unparalleled efficiency of contagious transmission among cervids. 2
• Eradication from endemic areas is considered very unlikely, and continued geographic expansion is expected. 1, 2

Practical Recommendations for Clinicians

Patient Counseling on Venison Consumption

• Advise patients to avoid consuming meat from deer or elk known to be CWD-positive or from areas with high CWD prevalence. 2, 4
• Recommend testing of harvested deer and elk in endemic areas before consumption, particularly for brain, spinal cord, eyes, spleen, tonsils, and lymph nodes which contain highest prion concentrations. 5, 2
• Emphasize that standard cooking temperatures do not destroy prions. 2

Surveillance Considerations

• Maintain awareness that CWD represents a theoretical zoonotic risk despite absence of confirmed human cases. 4
• Document detailed exposure history in patients presenting with unexplained progressive neurological decline who have consumed cervid meat from endemic areas. 3
• Recognize that clinical manifestation, if transmission occurs, could take decades to appear. 3

High-Risk Populations

• Hunters, game processors, and individuals who regularly consume wild cervid meat from CWD-endemic regions face the highest theoretical exposure risk. 5, 2
• Occupational exposure through handling infected carcasses represents a potential route, though no cases have been documented. 5