CWD prions confirmed in raw, cooked elk meat and water used for boiling, but risk to people unclear

Magnificent elk

Oregon Department of Agriculture / Flickr cc

Researchers have identified chronic wasting disease (CWD) prions in raw, cooked, and cured meat from an infected elk in Texas, confirming the presence of the infectious CWD-causing agents in muscle but concluding that the risk of transmission to humans through consumption is still unclear and requires continued vigilance.

Cooking temperatures are well known to be ineffective in disabling CWD prions, which are misfolded cervid (eg, deer, moose, elk) prions, leading to neurologic disease and death. The prions spread among cervids and through environmental contamination. There is no vaccine or treatment for CWD, which has been found in 35 US states, Canada, Norway, Finland, Sweden, and South Korea.

Team used highly sensitive tests

For the study, published late last week in Emerging Infectious Disease, a team led by University of Texas Health Science Center researchers used protein misfolding cyclic amplification (PMCA) and Western blot to test filets, jerky steak, hamburger, chili meat, sausage, ham, cutlets, and boneless steaks from a 5-year-old bull elk harvested in December 2020 on a Medina County high-fence hunting ranch. 

The elk hadn't shown signs of CWD, corresponding author Rodrigo Morales, PhD, of the University of Texas Health Science Center at Houston, told CIDRAP News. After meat processing, immunohistochemistry tests revealed CWD prions in the obex region of the animal's brain, but the lymph nodes weren't tested.

The first three PMCA rounds identified CWD prions in raw boneless steak, sausages and cutlets, and jerky, respectively. Grilling the meat to medium-well doneness substantially boosted PMCA detection of prions, and five samples of hamburger, chili meat, ham, cutlets, and boneless steak tested positive in a first PMCA round. 

Morales, who also contributed to a recently published CWD report by CIDRAP (Center for Infectious Disease Research and Policy, publisher of CIDRAP News), said the team isn't sure why heating led to greater detection of prions in the meat. 

"We believe that heat helps to disrupt some tissues that persist after homogenization," he said. "This disruption may help to release prions trapped in these tissues. However, we are not sure whether this has consequences in infectivity titers as well. We are currently addressing this question using mouse bioassays."

A second PMCA round found prions in jerky, and a third identified prions in all grilled and boiled meats. Boiling different cuts of the same samples produced similar results, and the water used to boil the meat was also CWD-positive on PMCA.

Using PMCA to estimate the zoonotic properties of prions—their ability to spread from animals to people—in raw and cooked meats showed that none of the meat samples could induce conversion of normal human prion protein to an abnormal, infectious form characteristic of prion disease, which the researchers say suggests limited zoonotic potential.

Continued surveillance needed

To validate the PMCA method used for modeling cross-species prion transmission, the researchers incorporated classic bovine spongiform encephalopathy (BSE, or "mad cow" disease) and sheep scrapie samples into the experimental protocol. Both of these are prion diseases.

Considering that humans consume products from ≈7,000–15,000 CWD-infected cervids each year, the need for clarification of transmission risk for prion diseases is imperative.

"We found PMCA reactions seeded by BSE prions and a CWD isolate were able to induce the misfolding of human PrPC [normal protein], as previously reported, but that sheep scrapie was unable to do so," the researchers wrote.

The study authors noted that, in addition to muscle, CWD prions have been previously detected in the lymph nodes, spleen, tongue, intestines, adrenal glands, eyes, reproductive tissues, ears, lungs, and liver, among other organs, in several species of infected cervids. Thus, experts worry about the safety of human consumption of cervid meat and underscore the need for continued surveillance and research to safeguard the human food supply.

"Considering that humans consume products from ≈7,000–15,000 CWD-infected cervids each year, the need for clarification of transmission risk for prion diseases is imperative," they wrote.

Cory Anderson, PhD, MPH, co-director of CIDRAP's CWD Program, said it's one of just a few studies he is aware of showing that CWD prions can be found in the skeletal muscle of infected elk. Anderson wasn't involved in the study.

"The first study that I know of was published in 2006 but only found prions in heart muscle, whereas a second study published in 2023 found prions in several other muscle tissues (eg, neck, legs, diaphragm)," he said. "Otherwise, most studies evaluating CWD prions in skeletal muscle tissue have focused on deer rather than elk."

Because of the potential implications to food safety and public health, the researchers said, the findings warrant further research. 

"Our results suggest that although the elk meat used in this study resisted different manipulations involved in subsequent consumption by humans, their zoonotic potential was limited," the study authors wrote. "Nevertheless, even though no cases of CWD transmission to human have been reported, the potential for human infection is still unclear, and continued monitoring for zoonotic potential is warranted."

This week's top reads

Our underwriters