Chronic Wasting Disease News Timeline:
March 31, 2022: CWD confirmed in North Carolina for the first time
February 7, 2022: CWD found in new Wyoming dear hunt area
February 4, 2022: First confirmed case of CWD found in Louisiana.
December 30, 2021: CWD detected in a buck in Warren County, Mississippi.
December 20, 2021: CWD confirmed in a new area in central South Dakota. Confirmation of the disease was obtained from a hunter-harvested adult female white-tailed deer in Buffalo County.
December 13, 2021: Tennessee IDs Chronic Wasting Disease in Deer in 13th County
December 6, 2021: Positive CWD test on Minnesota deer leads to management changes
May 2021: New case of CWD detected in Warren County, PA leads to establishment on new Disease Management Area (DMA5) in the state
March 3, 2021: Cornell Wildlife Health Lab’s Surveillance Optimization Project for Chronic Wasting Disease (SOP4CWD) Moving Forward
December 18, 2020: Elk Tests Positive for CWD in Grand Teton National Park, Near Elk Feedgrounds
December 1, 2020: Role of wolves in limiting the spread of Chronic Wasting Disease
July 9, 2020: National Wildlife Health Center June 2020 Newsletter Focused on Current & Collaborative work on CWD
June 26, 2020: Genetic clues help identify CWD susceptibility
May 20, 2020: Montana officials detect new cases of chronic wasting disease
As of April 2022, Chronic Wasting Disease (CWD) has been detected in free-ranging cervids in 29 U.S. states:
(Credit: Bryan Richards, USGS National Wildlife Health Center. Public domain.) Source: https://www.usgs.gov/centers/nwhc/science/expanding-distribution-chronic-wasting-disease
Additional Information on Chronic Wasting Disease (CWD)
Chronic wasting disease (CWD) is an emerging infectious disease that is fatal to wild and captive animals in Cervidae (deer) family. In North America, white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemionus), elk (Cervus canadensis), and moose (Alces alces) have all been documented to have infection with CWD.
Since its initial identification in Colorado and Wyoming in the 1960s and 1970s, CWD has spread and now affects cervids across North America.
CWD is one member of a family of diseases called transmissible spongiform encephalopathies (TSEs). The causative agents of TSEs are thought to be prions. Prions are misfolded proteins with the ability to trigger abnormal folding in other normal variants of the same protein. These prions accumulate in the brain and other tissues causing neurological signs, emaciation, and death.
The only prion disease known to affect free-ranging wildlife, CWD is increasing in prevalence in areas where the disease is already established. In heavily affected areas of Wyoming, Colorado, and Wisconsin, more than 40% of free-ranging cervids are infected. Wildlife biologists have documented population declines in white-tailed deer, mule deer, and elk due to CWD.
Clinical Signs of Chronic Wasting Disease
Infected animals lose weight and body condition, resulting in emaciation and death. Neurologic signs and behavior changes include depression, altered gait, head tremors, teeth grinding, hypersalivation, difficulty swallowing, circling, and ear droop. Once clinical signs are observed, the disease is generally fatal. Most animals survive a few weeks to several months after the onset of the clinical signs described above. Depending on the host species, the incubation period before signs appear may be as short as 12 months, but is often longer than 2 years. Clinically normal fawns as young as 5-6 months have tested positive for CWD.
Diagnosis
Clinical signs of CWD alone are not diagnostic as several other diseases cause similar symptoms. Diagnosis requires postmortem examination of the brain for spongiform lesions and/or accumulation of the CWD-associated prion in brain and/or lymphoid tissues. There is no practical way to test live animals for CWD.
Transmission
CWD prions are shed in saliva, urine, feces, blood, antler velvet, and carcasses of infected hosts. Transmission occurs by direct contact with live infected animals or indirectly through contact with contaminated environments. Prions are extremely resistant to heat, ultraviolet radiation, and disinfectants. They can persist in the environment for very long periods of time, sometimes years or even decades.
Surveillance
To estimate prevalence in free-ranging populations, tissues from clinically normal deer and elk harvested by hunters in CWD-endemic areas are collected and tested at random. The known distribution of CWD in captive and free-ranging cervids continues to increase but likely remains underestimated.
Management Strategies
Currently, effective treatment for CWD does not exist. To date, experimental vaccines have only shown prolonged incubation periods but have not provided complete immunity. Practices to prevent CWD transmission are limited, but remain our only option for control.
A variety of strategies for managing CWD transmission in free-ranging cervids have been employed. These include strictly regulating the shipping/translocation of deer, and banning the artificial congregation of cervids using supplemental feed, minerals, and/or bait. The Western Association of Fish and Wildlife Agencies (WAFWA) developed the Recommendations for Adaptive Management of Chronic Wasting Disease in the West. These recommendations include three primary strategies: reduce artificial points of host concentration, adjust hunting regulations with bias toward males (because prevalence in adult deer is generally highest in adult males- often double that of adult females), and develop harvest strategies using prior fall harvest information to maximize removal of infected animals.
Zoonotic Potential & One Health Aspects
Currently, there is no strong evidence that Chronic Wasting Disease can infect humans. Nevertheless, recent experimental studies raise the concern that CWD may pose a risk to people and suggest that it is important to prevent human exposures to CWD.
The CWD prion has been shown to experimentally infect squirrel monkeys, and also laboratory mice that carry some human genes. An additional study begun in 2009 is evaluating whether CWD can be transmitted to macaques. In 2017, the researchers presented initial findings that CWD was transmitted to monkeys that were fed infected meat or brain tissue from CWD-infected deer and elk. Furthermore, meat from asymptomatic deer was able to infect the macaques with CWD.
This study showed different results than a previous study that did not show successful transmission of CWD to macaques. The reasons for the different experimental results are unknown.
Until we have more information, public health officials recommend that human exposure to the CWD agents be avoided as research into the disease continues. Since 1997, the World Health Organization has recommended that it is important to keep the agents of all known prion diseases from entering the human food chain.
For more information:
Chronic Wasting Disease Alliance
USGS Article: Chronic Wasting Disease- Can Science Save Our Deer?
Chronic Wasting Disease Alliance
NWHC Chronic Wasting Disease Overview
Cornell Wildlife Health Lab CWD Fact Sheet
Recently Published CWD Research:
Hunting Pressure Modulates Prion Infection Risk in Mule Deer Herds
