Chronic Wasting Disease (CWD) is a slow and progressive transmissible neurological disease of deer, elk and moose caused by an infectious protein, or prion, which produces small lesions in the brains of infected animals. CWD is always fatal and is transmitted through direct animal to animal contact or by contact with saliva, urine, feces, blood, and carcass parts of an infected animal or infected soil. CWD is classified as a transmissible spongiform encephalopathy (TSE), and is similar to mad cow disease in cattle and scrapie in sheep.
The disease was long thought to be limited in the wild to a relatively small endemic area in northeastern Colorado, southeastern Wyoming and southwestern Nebraska, but has been found in several new areas across the North American continent. It first appeared in Wisconsin in 2002. The disease also has been diagnosed in commercial game farms in several states and provinces, including Wisconsin.
Clinical Signs of Illness
Because the disease has a long incubation period, deer, elk, and moose infected with CWD may not produce any visible signs of the disease for a number of years after they become infected. When they do, some of the most common signs of CWD are:
- Loss of body condition or emaciation.
- Change in behavior such as loss of fear of humans.
- Loss of bodily control or movements.
- Excessive drooling and salivating.
The only conclusive diagnosis involves an examination of the brain, tonsils or lymph nodes performed after death. A definitive diagnosis is based on examination of the brain for the characteristic microscopic spongiform lesions and/or accumulation of the CWD associated prion protein in brain and lymphoid tissues using a technique called immunohistochemistry.
Much research is being done to develop a live animal diagnostic test.
CWD can be highly transmissible within deer and elk populations. The mode of transmission is not fully understood, but evidence supports the possibility that the disease is spread through direct animal-to-animal contact or as a result of indirect exposure to prions in the environment (e.g., in contaminated feed and water sources).
Although CWD is a contagious fatal disease among deer, elk and moose, research suggests that humans, cattle and other domestic livestock are resistant to natural transmission. To date there has been no documented transmission of CWD to humans, however the Centers for Disease Control has tips for hunters to further minimize the risk of exposure.