Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) of mule deer, whitetailed deer, elk (or “wapiti”), and moose (“elk” in Europe). TSEs are caused by unusual infectious agents known as prions. To date, CWD has been found mainly in cervids (members of the deer family). First recognized as a clinical “wasting” syndrome in 1967 in mule deer in a wildlife research facility in northern Colorado, USA, it was identified as a TSE in 1978 and has spread to a dozen states and two Canadian provinces. CWD is typified by chronic weight loss leading to death. There is no known relationship between CWD and any other TSE of animals or people.