Researchers have drawn a possible link between the deaths of two hunters in the last couple of years from a rare neurological condition. A report, authored by medical experts from the University of Texas at San Antonio and published earlier this month in the clinical journal Neurology, suggests the men contracted it by consuming venison from deer infected with chronic wasting disease, a degenerative illness not conclusively shown to be transmissible from animals to humans.

Both men hunted at the same lodge and consumed meat from the same deer population before each developed Creutzfeldt-Jakob disease and died soon afterward, the report’s authors said. They did not give the lodge’s specific location. Creutzfeldt-Jakob disease is one of several prion diseases — uncommon neurodegenerative disorders affecting humans that are characterized by an abnormal folding of proteins in the brain, according to the Centers for Disease Control and Prevention. Symptoms broadly mimic those of dementia, although patients afflicted with Creutzfeldt-Jakob deteriorate much more quickly.

The new study centered around the initial death of a 72-year-old man in 2022 who “presented with rapid-onset confusion and aggression,” the authors said. That man apparently had a history of eating meat from a deer population known to be infected with chronic wasting disease. His friend, who had eaten venison from the same deer population, died later from Creutzfeldt-Jakob disease. 

The friend’s death came within a month of him developing symptoms typical of the illness, like seizures and agitation, according to the study, and a postmortem ultimately confirmed his diagnosis with a variant form of it called sCJDMM1. Authors said that finding may point to “a possible novel animal-to-human transmission of CWD,” although they acknowledged it did not definitely prove that consuming venison from a deer infected with chronic wasting disease eventually caused Creutzfeldt-Jakob disease in any human being. But that possibility could not be definitively ruled out, either.

“Although causation remains unproven, this cluster emphasizes the need for further investigation into the potential risks of consuming CWD-infected deer and its implications for public health,” they said in the report. CBS News contacted the report’s lead author for comment but did not receive an immediate response.

Prion diseases, including Creutzfeldt-Jakob disease, can have long incubation periods but progress rapidly once symptoms start to present themselves and are always fatal. While they are not well understood, exposure to certain pathogens that then trigger the brain proteins to fold is believed to be the cause. 

According to the Mayo Clinic, Creutzfeldt-Jakob disease is thought to emerge in four different ways: sporadically, the most common form, where someone develops the disease without a clear trigger; by inheriting certain genetic changes that cause prion proteins to develop; through contaminated medical instruments used during surgeries or other medical procedures, which is rare; and through consumption of contaminated beef, which is even rarer. 

A variant form of Creutzfeldt-Jakob disease has long been tied to eating beef from cattle infected with mad cow disease, or bovine spongiform encephalopathy, which is another prion disorder. The connection between the infections in cattle and humans who ate beef from those cattle gained international attention when it was recognized publicly by government health officials in the United Kingdom in the 1990s, following a string of disease outbreaks. 

Even though chronic wasting disease falls, along with mad cow, under the umbrella of prion disorders affecting animals, experts have said no strong evidence exists to indicate that prions seen in chronic wasting disease can infect humans. Some big questions remain about the disease’s transmission across species though, and there have been a few experimental studies that suggest, at least, that chronic wasting disease is transmissible to primates. The CDC writes in a discussion about prion transmission that, however experimental, those studies “raise the concern that CWD may pose a risk to people and suggest that it is important to prevent human exposures to CWD.”

Chronic wasting disease has been reported in free-ranging deer, elk and moose in 32 states across the continental U.S. and four Canadian provinces, as well as in some farmed deer and elk, according to the CDC. The agency has noted that the overall occurrence of the disease nationwide is relatively low, but it can spread quickly through populations where it has been established, and, in the event that it is established, “the risk can remain for a long time in the environment.” 

Several hundred deer have tested positive for the disease in Minnesota over the last 20 years or so, mainly in the southeastern part of the state, CBS Minnesota reported. Last year, experts said a captive deer in Wisconsin tested positive for the illness just a few months before officials in Yellowstone National Park announced they had detected the disease in a deer in that area for the first time.