Chronic wasting disease

Chronic wasting disease
Other names	Zombie deer disease
Deer with signs of chronic wasting disease
Specialty	Infectious disease, neurology, veterinary medicine
Symptoms	Behavioral changes, weight loss, decreased interactions with other animals, tremors, repetitive walking in set patterns, increased drinking and urination, excessive salivation and grinding of the teeth, loss of fear of humans, confusion
Usual onset	18–24 months after initial exposure
Causes	A type of prion
Diagnostic method	Suspected based on symptoms, confirmed by examination of the brain
Prevention	Exterminating infected deer, incineration and disposal of infected deer carcasses
Treatment	None
Prognosis	Always fatal[1]

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.^[2] Natural infection causing CWD affects members of the deer family. In the United States, CWD affects mule deer, white-tailed deer, red deer, sika deer, elk, bison, squirrels, antelope, caribou, and moose.^[3] The transmission of CWD to other species such as squirrel monkeys and humanized mice has been observed in experimental settings.^[4]

In 1967, CWD was first identified in mule deer at a government research facility in northern Colorado, United States.^[3] 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.^[5] 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.^[6] CWD is typified by chronic weight loss and clinical signs compatible with brain lesions, aggravated over time, always leading to death.

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".^[7] A 2019 study concluded that "the potential exists for transmission to humans and subsequent human disease".^[8] 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".^[7] In April 2024, it was revealed that two men from the same hunting group contracted CJD, prompting medical researchers to speculate transmission had occurred from consuming CWD-positive venison.^[9]