CWD is a fatal neurologic disease of cervids (e.g., deer, elk, moose, reindeer). It is caused by a misfolded form of a normal protein, known as a prion. The misfolded proteins aggregate in tissues, particularly the brain, causing progressive damage. CWD belongs to a group of human and animal diseases called transmissible spongiform encephalopathies (TSE). Examples of TSEs in animals include bovine spongiform encephalopathy (BSE) in cattle, also known as “mad cow disease,” and scrapie in sheep and goats, which has been known to veterinary medicine for over 200 years. Creutzfeldt-Jakob disease (CJD), a sporadic prion disease arising in 1:1,000,000 people, and variant Creutzfeldt-Jakob disease (vCJD), which has been linked to the consumption of infected cattle during the “mad cow disease” outbreak in Great Britain and Europe in the 1990s, are examples of TSEs in humans.
The misfolded prion that causes CWD is infectious to other cervids and can be spread through direct contact with infected individuals or through contact with a contaminated environment. Infectious prions can be excreted in urine, feces, and saliva of infected animals, even before they show any signs of the disease. Carcasses and tissues, especially brain, spinal cord, and lymph nodes, of infected animals contain infectious prions and may spread the disease if left out on the landscape. Prions are very stable and difficult to disinfect, persisting for years in a contaminated environment able to infect a susceptible deer or elk.
Chronic wasting disease (CWD) was first described in mule deer at a captive facility in Colorado in 1967. Since then, CWD has been diagnosed in deer, elk, and moose populations in 31 states and four Canadian provinces. It has also been found in captive elk and Sika deer in South Korea, free-ranging moose and reindeer in Norway, and free-ranging moose in Finland. For a map of current known CWD infected populations in North America, please visit the United States Geological Survey (USGS) CWD page. A timeline of the spread of CWD can be found by visiting the Chronic Wasting Disease Alliance website.
The progression of chronic wasting disease (CWD) in an infected animal is very slow. It takes months or even years following infection for clinical signs of CWD to appear. Infected animals gradually become skinnier, emaciated or “wasted” despite continuing to eat. They may show abnormal behaviors such as a wide stance, staggering gait, or inability to keep their head up.
To date, chronic wasting disease has never been detected in California’s deer or elk populations. If you see a sick or dead deer that could be due to CWD, please use our online mortality reporting form (preferred) or contact the CDFW Wildlife Health Laboratory directly at (916) 358-2790. It is important to note that many other conditions that affect deer in California can produce similar clinical signs. However, the Department’s Wildlife Health Laboratory investigates sick or dead wildlife and is particularly interested in deer and elk that display clinical signs consistent with CWD: skinny or “wasted,” abnormal behavior, staggering gait, head and ears lowered. Testing these animals for CWD is an integral part of ongoing CWD surveillance efforts in California, and we rely on members of the public to report sick and dead animals.
Prevention: Legislation and regulations enacted since the 1990's help keep the risk of importing the disease to a minimum. These include severely limiting the importation of captive deer and elk (and other cervids) into California (CCR Title 14, Section 671)), limiting what hunters can bring in from out-of-state hunts (no skull, no backbone) (CCR Title 14, Section 712)), and banning the feeding of wildlife to prevent artificially congregating susceptible animals (CCR Title 14, Section 251.3).
Surveillance: Since 1999, California has tested over 5,500 deer and elk for CWD, the majority from hunter-harvested animals. To date, no CWD has been found. In 2017, CDFW developed and implemented a statewide CWD surveillance plan, renewing our active CWD surveillance program and increasing yearly CWD testing goals. CWD prion has not been detected in any animal tested to date.
Management: CDFW initiated an interagency CWD Task Force to develop and implement a CWD management plan. The surveillance portion of that has been implemented and the task force is working to finalize the management plan.
There are no documented cases of CWD affecting a human. However, the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) recommend that hunters do not eat meat from deer that test positive for CWD or otherwise appear sick. In addition, CDFW recommends that hunters wear latex or nitrile gloves when field-dressing and processing animals, and that hunters wash their hands and disinfect tools after processing.
Currently, the only approved tests for CWD require lymph node or brainstem samples, taken after death, to detect the prion associated with CWD. However, this is an area of considerable research and we hope additional rapid and live-animal tests become available in the future.