For the first time, chronic wasting disease (CWD), a deadly ailment devastating deer populations elsewhere in North America, has been identified in California. State wildlife authorities confirmed the presence of the disease after examining samples from two deer—one found dead near Yosemite Lakes in Madera County and another struck by a vehicle near Bishop in Inyo County.
The detection of CWD in these disparate locations suggests the disease may have been present in California for some time, given its prolonged incubation period of months to years. Once infected, the disease is invariably fatal to deer and elk. CWD, often dubbed “zombie deer disease,” resembles bovine spongiform encephalopathy (mad cow disease) and attacks the nervous system of cervids, including deer, elk, and moose.
Although CWD does not pose a direct threat to human health, preventing its transmission to humans through the food chain remains a key concern. Since its initial discovery in 1967, CWD has spread to 34 states and five Canadian provinces. While previously detected in California, this marks the first time the disease has been found in deer or elk.
Unchecked, CWD could devastate deer herds across the state, particularly black-tail and mule deer populations in the Sierra Nevada foothills and coastal prairie mountains. Recognizable signs of the disease in animals include weight loss, uncoordinated movements, excessive thirst, and behavioral changes.
Combatting CWD has proven challenging, as the disease primarily spreads through contaminated soil where infected animals have shed prions—abnormal proteins that can persist for years. Early culling of infected populations has proven effective in some areas, but eliminating the disease entirely remains elusive.
California wildlife authorities have been vigilant in monitoring and testing deer and elk populations since 2000, conducting over 6,500 tests to date. Efforts to enhance surveillance involve collaboration with hunters, taxidermists, and meat processors. The public’s assistance in reporting signs of illness in deer and elk populations is crucial to limiting the spread of CWD, and hunters are encouraged to have their harvested animals tested for the disease.
