Chronic wasting disease was discovered in the 1950s when researchers observed deer in Colorado behaving like zombies, staggering around blindly as they starved to death.
The disease, caused by the spread of proteins called prions, has since been reported in Canada and some US states, including Michigan and Wisconsin.
No human has caught the disease, but a recent study suggests it could get into a person's brain if they were to eat meat from an infected animal.
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 lose weight, stop interacting with other deer, and lose its fear of humans, and it may start drinking and salivating more. It winds up staring vacantly as it starves to death, which is why the illness is also known as "zombie deer" disease.
As far as we know, though, no human has ever been infected with the disease, caused by the spread of misfolded proteins called prions.
But Canadian researchers have recently expressed concerns that the disease could infect people who eat deer, elk, moose, or others that carry the proteins.
Preliminary results from an ongoing study by a branch of Health Canada show that macaques, the primates most similar to humans that can be used in research, can catch the disease 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 in April. "The most prudent approach is to consider that CWD has the potential to infect humans."
The rise of a strange illness
Researchers first noticed this disease about 50 years ago in Colorado. Since then, it has been reported in neighboring states, those around the Great Lakes, including Wisconsin and Michigan, and Canada.
Prion illnesses are often progressive and usually fatal, and scientists think they can adapt to infect different types of species — including, potentially, humans. But they're not well understood.