Chronic wasting disease (CWD)—popularly known as “zombie deer disease”—has been reported in at least 24 states in the continental U.S. as of August 2019, in addition to two Canadian provinces.
CWD is a neurodegenerative disorder that can affect members of the cervid family, which includes deer, elk, reindeer, and moose, according to the Centers for Disease Control and Prevention (CDC.)
Scientists think the disease is the result of infection with mysterious pathogens known as abnormal “prion” proteins which damage normal proteins in the brain and spinal cord. Prion infections, such as mad cow disease, cause rapid neurological degeneration after the onset of symptoms.
CWD in particular causes holes to develop in the brain of infected animals, producing symptoms such as progressive weight loss (wasting,) listlessness, drooling, lack of awareness, lack of fear and aggression. In all cases, the disease is fatal to the animal, however, many don’t live long enough to experience many of the purportedly “zombie-like” symptoms.
The incubation period—or time between exposure to the pathogen and onset of symptoms—is 18-24 months, according to the U.S. Geological Survey. Thus, animals which are infected may appear perfectly healthy for months.
CWD was first discovered in 1967 and since then it has spread geographically and increased in prevalence locally. It can spread very easily among cervid populations, especially given that no treatment or vaccines are currently available.
Most cases of CWD have been reported in Western and Midwestern U.S. states, however, the disease has also been documented in other areas of the country as well as parts of Canada, Norway, Finland, and South Korea.
In the United States the actual occurrence of the disease is relatively low, according to the CDC. However, it can remain in an area for a long time, embedding itself in deer populations with infection rates that can be as high as one in four in the wild, and four in five in captive herds.
It is thought that CWD prions are transmitted directly through animal-to-animal contact, and indirectly through contact with infectious materials, such as saliva, urine, feces, blood and carcasses. The prions can persist in the environment for a long period of time and still remain infectious.
Currently, there have been no cases of CWD reported in humans. However, scientists say that more research is needed to understand whether or not people can indeed become infected. In any case, health authorities stress that the utmost precaution should be taken to prevent human exposure, in order to mitigate any risks that may exist.
“We could be having human transmission occurring today and we wouldn’t even know it,” Michael Osterholm, from the Center for Infectious Disease Research and Policy at the University of Minnesota, told The Independent.
These warnings are especially pertinent given that many people doubted mad cow disease could affect people during an outbreak in the U.K. before transmission to humans was documented after a period of several years.
Variant Creutzfeldt-Jakob disease—thought to be caused by eating beef infected with mad cow—eventually killed more than 150 people in the United Kingdom since the beginning of the mad cow outbreak in the 1980s.
“The key issue here is that unlike the mad cow disease, here we see [chronic wasting disease] in the muscle as well, so it’s actually much more present in the meat that you’re eating. Cooking doesn’t do anything to destroy it,” he said.
If CWD did turn out to be transmissible to humans, eating infected deer meat would probably be the most likely route of infection. Thus, the CDC recommends that hunters should not shoot, handle or eat meat from deer or elk that look sick or are acting strangely. If you do want to eat the meat, get it tested before doing so, the agency recommends.