Chronic wasting disease (CWD), sometimes called zombie deer disease, is a transmissible spongiform encephalopathy (TSE) affecting deer. TSEs are a family of diseases thought to be caused by misfolded proteins called prions and include similar diseases such as BSE (mad cow disease) in cattle, Creutzfeldt-Jakob disease (CJD) in humans and scrapie in sheep. In the United States, CWD affects mule deer, white-tailed deer, red deer, sika deer, elk, caribou, and moose. Natural infection causing CWD affects members of the deer family. Experimental transmission of CWD to other species such as squirrel monkeys and genetically modified mice has been shown. In 1967, CWD was first identified in mule deer at a government research facility in northern Colorado, United States. It was initially recognized as a clinical "wasting" syndrome and then in 1978, it was identified more specifically as a TSE disease. Since then, CWD has been found in free-ranging and captive animal populations in 30 US states and four Canadian provinces. In addition, CWD has been found in one Minnesota red deer farm, one wild reindeer herd in Norway (March 2016) as well as in wild moose. Single cases of CWD in moose have been found in Finland (March 2018) and in Sweden (March and May 2019, September 2020). CWD was found in South Korea in some deer imported from Canada. CWD is typified by chronic weight loss and clinical signs compatible with brain lesions, aggravated over time, always leading to death. No relationship is known between CWD and any other TSEs of animals or people. Although reports in the popular press have been made of humans being affected by CWD, by 2004 a study for the Centers for Disease Control and Prevention (CDC) suggested, "[m]ore epidemiologic and laboratory studies are needed to monitor the possibility of such transmissions". The epidemiological study further concluded, "[a]s a precaution, hunters should avoid eating deer and elk tissues known to harbor the CWD agent (e.g., brain, spinal cord, eyes, spleen, tonsils, lymph nodes) from areas where CWD has been identified". History Chronic wasting disease was first discovered by American wildlife veterinarian Beth S. Williams. Williams performed necropsies on deer and elk that had died of an unknown syndrome. She recognized that the brain lesions in these animals were consistent with transmissible spongiform encephalopathy (TSE). In 1978, she and neuropathologist Stuart Young cowrote the first scientific paper that named the disease and described it as