Chronic Wasting Disease (CWD) is a fatal neurologic disease of elk, deer, moose, and caribou for which there is no known cure. It belongs to a group of diseases called transmissible spongiform encephalopathies, a group which also includes bovine spongiform encephalopathy (“mad cow

disease”) in cattle, scrapie in sheep, and Creutzfeldt-Jakob disease in humans. CWD is caused by infectious, mis-folded proteins, called prions, that spread throughout the animal and result in organ damage and eventual death. These prions are found throughout bodily tissues and secretions and are shed into the environment before and after death. When other animals come in contact with the prions, either from infected animals or from contaminated environments, they can be infected. CWD does not appear to naturally infect cattle or other domesticated animals. The disease is slow acting, degenerative, and always fatal. The name comes from the appearance of symptomatic animals, which get very skinny and sick-looking before they die. There is no vaccine or cure for CWD.

The origin of CWD is unknown. It was discovered in 1967 in mule deer at a research facility in Colorado. Shortly thereafter it was also found in captive mule deer and elk in Ontario, Colorado, and Wyoming. By the 1990s, it was discovered in wild white-tailed and mule deer, elk, and moose in Colorado and Wyoming and among captive animals in Saskatchewan, South Dakota, Montana, and Oklahoma. As of 2021, it has been found in captive or free-ranging herds in 27 states, three Canadian provinces, Norway, Sweden, Finland, and South Korea.

CWD was first detected in the wild in Montana in 2017. By 2021, it had been detected across large portions of northern, eastern, and southern Montana. Click here to view a current map of where CWD has been found in Montana.

CWD affects members of the deer family, including elk, moose, mule deer, white-tailed deer, and caribou. CWD does not appear to naturally infect cattle or other domesticated animals.

Infected animals shed prions in saliva, feces, and urine during most of their infection and via bodily tissues and fluids upon death. These prions may remain infectious in the environment for at least 2 years (Miller et al. 2004). Transmission is believed to occur both through direct contact with infected individuals or via contact with contaminated environments.

Feeding wildlife such as deer is illegal and can congregate animals and lead to the rapid spread of disease. Furthermore, proper disposal of carcass waste in a landfill is believed to be important in preventing the human-assisted spread of the disease into new areas.

CWD has an average incubation period from infection to clinical signs of approximately 16 months, and the clinical phase may last an additional 4-9 months, culminating in death (Williams and Miller 2002, Williams et al. 2002, Tamguney et al. 2009). Thus, for much of the infection, deer and elk appear outwardly healthy. At the later stages of infection, poor body condition, neurologic symptoms, and secondary infections are common. There have been no documented recoveries from infection.

There is no known transmission of CWD to humans. However, The Centers for Disease Control and Prevention (CDC) recommends that hunters harvesting a deer, elk, or moose from an area where CWD is known to be present have their animal tested for CWD prior to consuming the meat, and to not consume the meat if the animal tests positive.

Some simple precautions should be taken when field dressing harvested animals:

• Wear rubber gloves and eye protection.

• Minimize the handling of brain and spinal tissues.

• Wash hands and instruments thoroughly after field dressing is completed. Instruments should be washed in a 40% bleach solution for 5 minutes.

• Avoid processing and consuming brain, spinal cord, eyes, spleen, tonsils, and lymph nodes of harvested animals (normal field dressing coupled with boning out a carcass will essentially remove these parts).

Miller, M.W., Williams, E.S., Hobbs, N.T. and Wolfe, L.L., 2004. Environmental Sources of Prion Transmission in Mule Deer. Emerging Infectious Diseases, 10(6), p.1003.

Tamgüney, G., Miller, M.W., Wolfe, L.L., Sirochman, T.M., Glidden, D.V., Palmer, C., Lemus, A., DeArmond, S.J. and Prusiner, S.B., 2009. Asymptomatic deer excrete infectious prions in faeces. Nature, 461, pp. 529–532.

Williams, E.S. and Miller, M.W., 2002. Chronic wasting disease in deer and elk in North America.

Revue Scientifique et Technique (International Office of Epizootics), 21(2), pp.305-316.

Williams, E.S., Miller, M.W., Kreeger, T.J., Kahn, R.H. and Thorne, E.T., 2002. Chronic wasting disease of deer and elk: a review with recommendations for management. The Journal of Wildlife Management, 66(3), pp.551-563.