Concerns about chronic wasting disease have heightened after a case report surfaced of two hunters who developed neurological disorders and died after eating venison from a population of deer that may have been infected with "zombie deer disease."

The report of the two hunters who died in 2022, presented in early April at the annual meeting of the American Academy of Neurology, did not prove the transmission of chronic wasting disease (CWD) from deer to humans, the University of Texas Health Science Center at San Antonio researchers wrote.

However, the researchers wrote, the case "emphasizes the need for further investigation into the potential risks of consuming CWD-infected deer and its implications for public health."

There have been no cases of CWD in people reported to date, according to the Centers for Disease Control and Prevention. But past studies raised concerns that CWD could "pose a risk to people," the CDC has said, suggesting "it is important to prevent human exposures to CWD."

Here's what to know about the hunters' deaths and the CDC's response to the report.

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CDC: Deer meat did not lead to hunters' illnesses, death

About the 2022 report, the agency agreed with the researchers "that there is a need for careful investigation of chronic wasting disease (CWD) as a potential risk to people's’ health," CDC epidemiologist Ryan Maddox said in a statement to USA TODAY.

But the CDC reviewed the 2022 cases and considered the two men's deaths as "part of the normal number of cases of CJD (Creutzfeldt-Jakob disease) we see in the U.S.," he said.

The men died after developing Creutzfeldt-Jakob disease (CJD), which like CWD is a prion disease, a class of fatal neurological disorders, which can affect humans and animals, and usually progress rapidly and are always fatal. In prion diseases, certain proteins in the brain begin to fold abnormally, causing brain damage and other symptoms, the CDC says.

"A history of hunting and/or eating venison does not mean that someone got CJD that way," Maddox said. "Many Americans hunt and even more eat venison. Some will develop sporadic CJD by chance and others will not."

What is chronic wasting disease?

Chronic wasting disease (CWD), in deer, elk and other animals, leads to weight loss, lack of coordination, stumbling, listlessness, weight loss, drooling, and lack of fear of people, hence the term "zombie deer disease." 

First identified in captive deer at a Colorado research facility in the late 1960s, CWD emerged in wild deer in 1981 and has since been reported in free-ranging deer, elk and moose in 33 states, according to the U.S. Geological Survey.

Scientists have been concerned about CWD because mad cow disease, or bovine spongiform encephalopathy, or BSE, jumped to humans in the United Kingdom in the 1990s.

"We know that prion diseases can spread from animals to people, as we saw with (mad cow disease)," Maddox said. "Studies are ongoing to assess whether CWD might pose a risk to people. Increases in the annual number of CJD cases in the United States can be explained by the aging population, improved surveillance, and better testing."

Aspects of the two hunters' cases point to classic Creutzfeldt-Jakob disease (CJD), rather than a newer neurological disorder caused by CWD, he said.

Prion diseases typically take many years to cause symptoms in people. "The men died from CJD either before or around the same time that CWD was found in the area where they hunted, leaving no time for a lengthy incubation period," Maddox said.

Their ages, symptoms and brain changes "were all consistent with what we normally see in classic, sporadic CJD not attributed to CWD," he said. When variant CJD emerged as a result of "mad cow disease," those affected were younger with different symptoms, Maddox said.

And ongoing studies do not show an increase in rates of CJD in hunters in Colorado. "Results so far have been reassuring," he said. "The number of cases of CJD or other prion disease in this hunting population has not been higher than what we would expect in the general population."

Chronic wasting disease: Tips to lower risk when hunting deer and elk

Even though CWD hasn't transmitted to humans, hunters should take precautions to avoid exposure to chronic wasting disease. Here's some tips from the CDC:

• Do not shoot, handle or eat meat from deer and elk that look sick or are acting strangely. Similarly, don't handle or eat roadkill.
• Wear latex or rubber gloves when field-dressing the animal or handling the meat. Do not use household knives or other kitchen utensils for field dressing.
• Avoid handling the organs of the animal, particularly the brain or spinal cord tissues.
• Check state wildlife and public health guidelines to see if CWD testing of animals is recommended or required where you hunt.
• Strongly consider having the deer or elk tested for CWD before you eat the meat. If your animal tests positive for CWD, do not eat meat from that animal.
• If you have your deer or elk commercially-processed, consider asking that your animal be processed individually to avoid mixing meat from multiple animals.

Follow Mike Snider on X and Threads: @mikesnider & mikegsnider.

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