The so-called “zombie disease” has been reported in deer, elk, and moose across 24 US states, according to a new warning by the US Centers for Disease Control and Prevention (CDC).

As of January 2019, at least 251 counties across the US, from northern Montana to southern Texas, have reported CWD in free-ranging cervids, members of the deer family. Farther afield, there are similar concerns for reindeer in Norway, Finland, and, to a lesser extent, South Korea.

Scientifically known as chronic wasting disease (CWD), the contagious neurological disease gets its sensational nickname because of its effect on the brain of cervids, including North American elk or wapiti, red deer, mule deer, black-tailed deer, white-tailed deer, sika deer, reindeer, and moose. Deer that have been struck with the disease suffer from drastic weight loss, abnormal behavior, stumbling, drooling, lack of coordination, aggression, excessive thirst, and a fear of others.

CWD is actually not believed by most to be caused by a bacteria, virus, parasite, or fungi. Instead, it appears to be a prion disease, a group of neurodegenerative diseases caused by “rogue” misfolded proteins building up in the brain. Once one prion is formed, these rogue proteins can “convert” more of the normal protein into their abnormal form, setting off a chain reaction that results in a build-up of prions in the brain. Humans can suffer from an unrelated prion disease known as Creutzfeldt-Jakob disease.

A CDC map is based on the best-available information from multiple sources, including state wildlife agencies and the United States Geological Survey (USGS). CDC

However, that’s just one theory. Another theory claims that the culprit behind the disease is a bacterium called spiroplasma.

It sounds pretty scary, but do you need to board up your doors and stock up on tinned food? Of course not. Scientists don’t fully understand the disease – which probably doesn’t sound too reassuring – but there’s no confirmed evidence that it can be transmitted to humans from deer. It doesn’t seem to infect cattle or other domesticated animals either.

The main concern is for free-roaming cervids. Even then, the CDC notes that “Nationwide, the overall occurrence of CWD in free-ranging deer and elk is relatively low.”

“In several locations where the disease is established, infection rates may exceed 10 percent (1 in 10), and localized infection rates of more than 25 percent (1 in 4) have been reported,” according to the CDC. “The infection rates among some captive deer can be much higher, with a rate of 79 percent (nearly 4 in 5) reported from at least one captive herd.”