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Chronic Wasting Di sease (CWD) causes nervous system degeneration in cervid animals (the deer family) in North America. CWD, like Creutzfeldt-Jakob disease (CJD) and bovine spongiform encephalopathy (so-called mad cow disease), belongs to a family of neurological diseases called transmissible spongiform encephalopathies (TSEs). TSEs are caused and spread by abnormal proteins called prions found in the central nervous system and the immune system. Prions are transmitted much like other infectious agents such as viruses and bacteria-mostly through direct contact between infected and healthy individuals, though prions may also persist in soil. Cervids that live in highly social herds and at high population densities are most likely to catch and transmit the disease. Infected animals develop lesions on the brain, lose body mass, and display behavioral abnormalities. All cases are fatal.
CWD was first observed among deer and elk in wildlife research facilities and game farms during the late 1960s, exclusively in the Rocky Mountain region. In subsequent years, cases appeared on game farms across the northern Rockies and the central plains of the United States and Canada. Wildlife pathologists discovered cases among free-ranging cervids in the Rockies in the early 1980s. By spring 2006, CWD had been detected in free-ranging cervids in 13 states and provinces, as far east as New York and as far south as New Mexico, and in captivity in several other states and provinces.
Wildlife pathologists have linked the spread of CWD with high population densities of cervids, as are found both on game farms and in regions where humans have intentionally and unintentionally created ecological conditions favorable for deer. As game farming blossomed in the 1990s, transport of infected animals between farms greatly aided the spread of CWD. CWD has killed up to 90 percent of game animals on some farms, and the United States Deparment of Agriculture has restricted the transport of animals between states. In regions such as the upper Midwest, where suburbanization and agriculture have facilitated high densities of white-tailed deer, CWD has spread rapidly among free-ranging deer. Furthermore, because of the cultural and economic importance of hunting, many residents favor a high deer population, and some tourist businesses maintain baiting stations-ideal sites for the spread of CWD. Illinois and Wisconsin have established additional hunting seasons to reduce deer populations within the area where the disease was most prevalent. Many states have enacted partial bans on deer baiting. These policies sparked controversy where hunting and game farms are economically important; some hunters and businesses dependent on hunting charge that wildlife managers exaggerate the extent of CWD. Many state wildlife management agencies also test all cervid animals killed during the regular hunting season as a surveillance measure.
CWD is most widespread in white-tailed deer, mule deer, and elk; it exists very rarely in free-ranging moose. Though bovine spongiform encephalopathy has been documented in humans as a variant of CJD, there are no known human cases of CWD. Neither have domestic livestock such as cattle contracted CWD. Many hunters, farmers, and taxidermists, however, have expressed fear that prions could spread through consumption of venison, contact between livestock and infected cervids, or handling of organs, brains, and spinal fluid.
- Paul Robbins and April Luginbuhl, “The Last Enclosure: Resisting Privatization of Wildlife in the Western United States,” Capital Nature Socialism (v.16, 2005);
- Elizabeth S. Williams and Ian Barker, eds., Infectious Diseases of Wild Mammals (Iowa State University Press, 2001).