A misfolded protein is spreading through deer herds across North America
Chronic wasting disease was first spotted in captive mule deer in Colorado in 1967. It is caused by prions, rogue proteins that force healthy ones to misfold, and it is always fatal. It now turns up in wild and farmed herds across 33 US states and five Canadian provinces.
The illness belongs to the same family as mad cow disease, scrapie in sheep and Creutzfeldt-Jakob disease in people. Researchers at a government facility in northern Colorado initially described it simply as a wasting syndrome; only in 1978 was it recognised as a transmissible spongiform encephalopathy. In the United States it affects mule and white-tailed deer, elk, red and sika deer, caribou and moose. It has also reached a wild reindeer herd in Norway in 2016, single moose in Finland and Sweden, and South Korea, via deer imported from Canada.
The culprit is a misshapen version of the normal prion protein found in nerve tissue. Once present, the abnormal form converts correctly folded copies into its own shape, setting off a chain reaction; as it accumulates in the brain, nerve cells degenerate. Genetics shapes the outcome. In elk, animals carrying two copies of the leucine variant at codon 132 seem to resist symptoms, while other combinations bring much faster onset. White-tailed deer with a particular variant at codon 96 take longer to fall ill.
Because signs take 18 to 24 months to appear, most sick animals are adults; the youngest known case showed symptoms at 15 months. Weight loss is the most reliable signal. Affected deer become listless and withdrawn, hang their heads, tremble, pace fixed routes, drool, grind their teeth, drink and urinate more, and lose their fear of people. The heavy drinking and drooling may help the disease spread.
Whether people can catch it remains unsettled. Research commissioned in 2004 by the US Centers for Disease Control and Prevention called for more monitoring, and a 2019 study said transmission to humans was possible. Laboratory work has shown it can pass to squirrel monkeys and to mice engineered with human genes. In April 2024 two men from one hunting party were reported to have developed Creutzfeldt-Jakob disease, leading researchers to speculate about infected venison.
Source: Chronic wasting disease
