Researchers are worried that a brain illness known as 'zombie deer' disease may start infecting humans

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• Chronic wasting disease was discovered in the 1950s after researchers observed deer in Colorado behaving like zombies, staggering around blindly as they starved to death.
• The disease - which is caused by spreading proteins called prions - has since spread to Canada and other US states including Michigan and Wisconsin.
• No human has caught the disease yet, but a new study suggests it could potentially get into the brain of a person who eats meat from an infected deer.

When a deer gets infected with chronic wasting disease, it can take up to two years before signs of the illness become visible.

At some point, the animal will start to lose weight, stop interacting with other deer, lose its fear of humans, and may start drinking and salivating more. Ultimately, it winds up staring vacantly as it starves to death. That's why the illness is also known as "zombie deer" disease.

The disease is similar to mad cow disease and is caused by the spread of misfolded proteins called prions. As far as we know, no humans have ever been infected with chronic wasting disease (CWD).

But Canadian researchers recently announced that they're concerned the disease could potentially start to infect humans that eat deer, elk, moose, or other members of the same animal family that carry the proteins.

Preliminary results from an ongoing study by the Health Products and Food Branch of Health Canada show that macaques, the primates most similar to humans that can be used in research, can catch CWD after regularly consuming infected meat.

Because of that, "the potential for CWD to be transmitted to humans cannot be excluded," Health Canada said in an advisory. "[T]he most prudent approach is to consider that CWD has the potential to infect humans."

CDC

As of January 2018, there were 186 counties in 22 states with reported CWD in free-ranging animals like deer and elk.

The rise of a strange illness

Researchers first noticed this disease about 50 years ago in Colorado. Since then, it has spread to neighboring states, Canada, and several states around the Great Lakes including Wisconsin and Michigan.

Prion illnesses are caused by the spread of misfolded proteins that cause other proteins to deform. They are often progressive and usually fatal, and scientists think they have the ability to adapt to infect different types of species - including, potentially ourselves. But such illnesses are not well understood.

The similar illness mad cow disease became a problem after cattle ate bone meal from sheep with a neurodegenerative disease. Once this illness made its way into the human food supply, it eventually caused a new type of Creutzfeldt-Jakob Disease, which causes rapid brain deterioration, in people.

Immunologist Mark Zabel of Colorado State University told Colorado Public Radio that because chronic wasting disease is still a newly discovered condition, it may evolve rapidly, which "leads us to believe it's only a matter of time before a prion emerges that can spread to humans."

For now, some experts recommend that hunters who harvest deer and elk in affected areas get a sample of their kill tested before grilling up any venison steaks. If the test comes back positive, they recommend discarding the meat.