Deer across North America are dying from a mysterious disease that gradually destroys the animal’s nervous system, and National Public Radio recently reported that scientists are concerned about the possibility of human infection.

Chronic wasting disease — or “zombie deer disease” — was first observed in 1967 in Fort Collins, Colorado, and has since infected wild herds in 25 states and Canada, as well as in South Korea and Norway, NPR reported.

A 4-year-old doe killed in Michigan this month was tested positive for the fatal nervous system disease, plus two deer in Mississippi.

Direct contact is one but not the only way the disease can be transmitted; the faulty proteins that cause the disease can coat plants and soil for years to decades. Symptoms, which may not show for up to two years, can include a vacant stare, thick saliva, exposed ribs, or drooping heads.

No cases in humans have been reported. There is strong evidence neither for nor against the possibility of human infection, which is what worries scientists. Research done at Colorado State University found that a macaque monkey contracted the disease after eating infected deer meat.

Fortunately, wildlife authorities in Colorado and Pennsylvania are pushing for hunting regulations to fight the spread of the disease among their local deer populations, according to the Denver Post.

Read the full story on the Atlanta Journal-Constitution here.