What is CWD?
Chronic wasting disease (CWD) is a neurological disease affecting the cervid family – deer, elk, moose, reindeer and caribou. It causes characteristic spongy degeneration in the brain of an infected animal.
CWD belongs to a group of diseases known as transmissible spongiform encephalopathies (TSEs). TSEs are believed to be caused by prions, which are abnormal proteins that self-replicate within an infected animal. Prions are highly resistant to disinfectants, heat or freezing. There are no vaccines or treatments for TSEs, and they always are fatal. Several other variants of TSEs exist including:
- Scrapie, which has been identified in domestic sheep and goats for more than 200 years
- Bovine spongiform encephalopathy (BSE) in cattle (also known as "mad cow disease")
- Transmissible mink encephalopathy in farmed mink
- Classic Creutzfeldt-Jakob Disease in humans (occurs naturally in about one out of every one million people worldwide)
- Variant Creutzfeldt-Jakob disease in humans has been associated with the large-scale outbreak of BSE in cattle herds in Great Britain.
CWD was first recognized in a captive mule deer at a wildlife research facility in Colorado in the late 1960s. CWD has been detected in wild and/or captive animals across 26 states, three Canadian provinces, South Korea, Finland, Norway and Sweden. It has been detected in white-tailed deer, mule deer, elk, European red deer, sika deer, Manchurian Sitka deer, moose, reindeer and caribou.
- How is CWD spread?
It can be spread from both direct (animal-to-animal) and indirect (environmental) contact with infected deer. Prions are shed through saliva, urine, blood, feces and antler velvet. Additionally, carcass parts from a dead infected deer can serve as a source of further infection to other deer in the area. By concentrating deer on the landscape through artificial feeding, or by providing attractants such as salt licks, humans can increase the likelihood of both direct and indirect contact.
- What are the symptoms in deer?
CWD is a slow, progressive disease. It can incubate for 1½ to 3 years before clinical signs begin to appear. This means that older deer, males in particular due to their rutting behavior which increases deer interactions, have the highest infection risk.
Throughout most of the infection period, the deer appears to be healthy, but is continually spreading the disease. Clinical signs include:
- Weight loss, emaciation
- Excessive drooling and salivation
- Loss of fear of humans
- Loss of body control, tremors or staggering
- Drooping head or ears
- Apparent confusion
- How do you test for CWD?
There is currently no practical live animal test to determine if CWD is actively infecting a deer. In order to confirm a diagnosis, lymph nodes or brain tissue must be tested.
An initial screening test, called an enzyme-linked immunosorbent assay (ELISA), is conducted which can isolate and detect the abnormal proteins (prions) if they are present in the tissue. If prions are detected, the remaining tissue is sent for a confirmatory test using immunohistochemistry (IHC).
The U.S. Department of Agriculture (USDA) has approved the IHC staining and examination of brain or lymph nodes in order to confirm an animal is positive. If an animal passes the first screening test (ELISA) and no prions are detected, that animal is reported as "not detected" for CWD.
- History of CWD in Minnesota
The DNR conducts CWD surveillance of wild deer based on risk from known positive cases in an effort to keep Minnesota's deer healthy. Proactive surveillance and precautionary testing for the disease is a proven strategy that allows the DNR to manage for CWD by finding it early, allowing for quick and aggressive actions to control it.
Since 2002, more than 71,000 wild deer have been tested for CWD in Minnesota; the disease was first detected in wild deer in Minnesota in 2010. The DNR conducts intense, concentrated surveillance in areas around known positives (both within a captive cervid farm or near our neighboring states' borders) for a minimum of three years after an infection is discovered to ensure the disease has not transferred to wild deer in Minnesota.
CWD has also been detected in deer/elk farms in the state. In Minnesota, farmed cervids are classified as livestock and managed by the Minnesota Board of Animal Health. The Department of Natural Resources has no authority to oversee or regulate the farms or the animals. To learn more about farmed cervid management and the Board of Animal Health's responsibilities, please see the review that was recently completed by the Office of the Legislative Auditor.
- Minnesota CWD Timeline
A CWD-positive elk farm found in Aitkin County. This marks the first CWD positive animal in Minnesota and DNR's first concentrated surveillance effort in wild white-tailed deer.
A CWD-positive elk farm in Stearns County discovered. This is a trace-out from the Aitkin County farm. DNR granted legal authority to open and close seasons, restrict feeding and impose rules to limit disease spread.
DNR completes 3-year statewide surveillance project. In total, 28,000 deer were tested and the disease was not found.
A CWD-positive white-tailed deer farm is discovered in a mixed deer/elk farm in Lac Qui Parle County.
A CWD-positive elk farm in Olmsted County is discovered. The United States Department of Agriculture (USDA) determines there has been an apparent long-standing infection within the herd. DNR implements the response plan, which calls for three years of surveillance in the area around the facility.
A wild CWD positive white-tailed deer is discovered within two miles of the CWD positive elk farm in Olmsted County. DNR's response plan requires that intense surveillance be conducted around the area of infection. This deer was discovered during the second year of the surveillance program.
A new CWD management zone (Deer Permit Area 602) is created and DNR begins three years of surveillance around the infected farm.
A farmed European red deer is found infected with CWD in a facility in Ramsey County. DNR's response plan is implemented, which calls for three years of surveillance in the area around the facility.
DNR completes three-year intensive CWD surveillance around the Olmsted county elk farm. More than 4,000 wild deer are tested in the immediate area and no additional positives are detected.
CWD discovered in wild deer in Alamakee County, Iowa, which borders Minnesota's Houston County. DNR tests 400 deer along the border but detects no disease. DNR completes three years of CWD surveillance around the Ramsey county European red deer farm with no positives found.
Ongoing detections of CWD positive wild deer in southwestern Wisconsin and northeastern Iowa prompted DNR to conduct voluntary surveillance in southeast Minnesota. During the 2016 deer season, three positive wild deer (adult males) are found in Fillmore County near Preston. DNR implements its response plan, which calls for an aerial survey of the area to assess deer numbers in the area and the collection of additional samples to assess disease prevalence and distribution. CWD Management Zone (Deer Permit Area 603) is created to enforce additional restrictions on deer feeding and carcass export restrictions. A CWD-positive deer farm is discovered in Crow Wing County. DNR implements its response plan, which calls for three years of surveillance in the area around the facility.
Winter: Eight additional CWD positive wild deer are found in DPA 603 during the Special Late Hunts, Landowner Shooting Permit phase and USDA agency culling during winter 2017. Spring: A CWD-positive deer farm is discovered in Meeker County. This farm is a trace-out from the Crow Wing County farm. The DNR implements its response plan, which calls for three years of surveillance in the area around the facility. Fall: Mandatory surveillance is conducted during the opening weekend of the firearm season in north-central and central Minnesota surrounding the recently detected CWD positive farms in Crow Wing and Meeker counties. Mandatory surveillance also occurs in southeast Minnesota in all deer permit areas surrounding and including DPA 603. Six additional CWD-positive wild deer are discovered within DPA 603. No positives are found in the north-central or central surveillance areas. Another CWD-positive deer farm is discovered in Winona County. All nine captive deer on this farm were infected. This farm is within the southeast surveillance area, but three years of surveillance will be conducted around this facility.
Fall: Mandatory surveillance during the opening weekend of the firearm season continues in the north-central and central parts of the state around the Crow Wing and Meeker County positive deer farms. Since no disease was found in 2017, the surveillance zone is a smaller area directly around the farms. Fall: Mandatory surveillance is expanded in the southeast due to the CWD positive deer farm in Winona County, new positive wild deer found in Eau Clair County, Wisconsin, and the ongoing detection of positive wild deer in DPA 603. Detected in 16 wild deer in Fillmore County, one wild deer in Houston County, and found again in the captive cervid facility in Crow Wing County where positive deer were found in 2016.
Winter: CWD is first found in one wild deer in Crow Wing County near a CWD-positive deer farm. Seventeen additional CWD-positive wild deer are found in southeastern Minnesota during the landowner shooting permit phase and USDA agency culling. Fall: Mandatory surveillance during the opening weekend of the firearm season continues in central Minnesota around the Meeker County positive deer farm. This fall will be the final year of surveillance in this area if the disease is not found this deer season and an adequate number of samples are collected. Fall: Mandatory surveillance is expanded in the southeast due to the CWD-positive wild deer in Houston County. The previous disease management area (deer permit area 603) is dissolved back to the historic deer permit areas and replaced by a 600-series of deer permit areas that signify disease management areas. A control zone (deer permit areas 255, 343 and 344) is established on the border of the disease management zone; carcass movement restrictions are in place in both these zones. Fall: A new CWD management zone (deer permit area 604) is created in north central Minnesota, in a 15-mile radius around the CWD-positive wild deer found in February 2019 and the CWD-positive cervid facility in Crow Wing County.