Chronic wasting disease (CWD) is a prion disease that affects several cervid species: deer, elk, reindeer, sika deer, and moose. CWD was first identified in 1967 in a captive mule deer living in a Colorado research facility. In 1981, CWD was detected for the first time in a wild cervid. Since these initial detections, CWD has been identified in 26 states and three Canadian provinces. It has also been detected in Finland, Norway, South Korea, and Sweden.
CWD is believed to be transmitted horizontally (i.e., animal-to-animal contact) through infectious bodily fluids such as saliva, urine, and feces. Once excreted into the environment, CWD prions can persist for years and withstand extremely high levels of disinfectants such as heat, radiation, and formaldehyde. CWD prions also are capable of binding to certain plants, with the ability to be transported while still remaining infectious. CWD is increasing in cervids as more animals come into contact with infectious prions, usually via direct contact with an infected cervid and its bodily fluids, although viable CWD prions in the environment can also infect animals. As more cervids become infected, the frequency of these exposures and subsequent environmental contamination grows. Evidence also suggests that vertical transmission (i.e., parent to offspring) can occur, although its overall impact on the ecology of CWD is not entirely understood at this time.
Since CWD is now an established wildlife disease in North America, proactive steps, where possible, should be taken to limit transmission of CWD among animals and reduce the potential for human exposure. Although CWD has not yet been found to cause infections in humans, numerous health agencies have taken the stance that people should not be consuming CWD-positive animals. Since 1997, the World Health Organization has recommended that agents of any prion disease should not enter the human food chain. Likewise, the US Centers for Disease Control and Prevention, Health Canada, and multiple provincial and state health and natural resources agencies recommend that people should not consume the meat of an animal found to be positive for CWD.
Given the typical ten year or longer incubation period of prion-associated conditions, improving public health measures now to prevent human exposure to CWD prions and to further understand the potential risk to humans may reduce the likelihood of an event like bovine spongiform encephalopathy (BSE). In BSE, also known as "mad cow" disease, some British officials in the 1990s declared there was no risk of transmitting BSE prions through the consumption of contaminated beef, only to confirm related human cases of a similar prion disease in the ensuing years.