About Chronic Wasting Disease (CWD) in Colorado
CWD is one area of increasing concern across Colorado. We need to find adaptive management tactics for helping prevent further spread of CWD and controlling it in herds that are already affected.
Controlling chronic wasting disease is critical for the long-term health of our herds. Our quality of life, outdoor heritage, and economic prosperity are dependent on the health and sustainability of these treasures.
CPW staff have worked for well over a century to ensure the health and future of Colorado’s state parks and wildlife for our citizens. Through cutting edge science and innovative conservation practices, we continue to push the boundaries of science to better understand how disease affects the wildlife of Colorado and what practices we can employ to address these challenges.
These resources form the very fabric of our state and define who we are.
Video Series: Seeing is Believing
This short two-part documentary film is increasing awareness about chronic wasting disease (CWD) to help people “witness” this disease through the eyes of others.
Ride along with Josh Melby, CPW District Wildlife Manager, as he speaks on the importance of working with private landowners to address CWD. Hear from landowners about their personal experiences with CWD on their properties.
Listen to wildlife professionals from Colorado and Wyoming speak to what we’ve learned about CWD and the importance of teamwork to manage the disease.
What is Chronic Wasting Disease?
CWD is an always-fatal disease of deer, elk and moose.
CWD is not caused by a virus or bacteria, it cannot be treated or prevented through vaccination.
This makes it a real threat to the health and long-term sustainability of herds if not controlled through active management.
How does CWD spread?
- CWD spreads through direct or indirect contact between animals. The disease agents, prions (pree-ons ) are present in saliva, feces and carcass parts of infected animals.
- These prions also can stay in the soil for long periods of time which is why it is also very important to monitor and control herds that are infected in order to minimize long-term contamination of their ranges with CWD prions.
Where is This Disease Found?
Chronic wasting disease occurs in free-ranging and captive cervids (members of the “deer” family) in several parts of North America, including Colorado.
The maps and tables below represent the results from the agency’s mandatory chronic wasting disease (CWD) testing for deer and elk since 2017. As of April 2024, CWD has been detected in 42 of our 51 deer herds, 17 of 42 elk herds, and 2 of 13 moose herds. Disease prevalence (percent infected) is highest in deer and lowest in moose. The percentage of sampled animals infected (or “prevalence”) appears to be rising in many affected Colorado herds.
Background
In the early-mid 2000s, hunters were very interested in learning whether their deer or elk was CWD positive. Results from large numbers of voluntary submissions showed most herds were low-prevalence or CWD was undetected.
Thereafter, voluntary submissions sharply declined. By 2010, trends in prevalence became difficult to track because too few hunters voluntarily submitted samples for testing. As a result, prevalence estimates for most herds were unreliable.
However, even with small submission numbers, a high proportion of animals tested positive in some herds, which indicated that prevalence had likely increased. In 2017, CPW resumed mandatory submissions from hunter-harvested deer to boost sample sizes and develop a clear understanding of how CWD trends had changed.
Expanded testing
Expanded testing is part of CPW’s Colorado Chronic Wasting Disease Response Plan, a 15-year plan that will rotate mandatory testing of hunter-harvested deer around the state to monitor CWD prevalence. The plan also provides a suite of tactics that CPW wildlife managers can use to reduce CWD prevalence in a deer herd. Management actions will be taken in a deer herd when prevalence exceeds 5% in adult bucks (>1 in 20 adult bucks). Deer and herds will be tested approximately every 5 years to learn how prevalence has changed between periods of mandatory testing.
2022 and 2023 Mandatory CWD Testing Results
In the 26 herds included in a second round of mandatory testing, CWD prevalence estimates decreased in 4 deer herds, remained about the same in 12 deer herds, and increased in 10 deer herds. Additional data and robust analyses are needed over the next 8 years of mandatory testing to guide our interpretation of these results before we are in a position to show an association between prescribed management actions and CWD prevalence. However, these preliminary data are encouraging and suggest harvest-based management actions could be a promising CWD control strategy. Considering that various management actions were prescribed to each of the 26 herds, CPW will need to evaluate why prevalence increased in some herds and decreased in others.
Further Analyses
CPW will continue analyses of these CWD prevalence changes by comparing various factors between herds and the respective management actions prescribed. Comparing changes to license quotas by season, dates of harvest and prevalence estimates by season, post-hunt buck/doe ratios, abundance of bucks and does, and the percent change in buck licenses and buck harvest, etc., all in relation to changes in CWD prevalence, should improve our ability to evaluate relationships between various management actions and disease prevalence.
In our more than 40-year history working with CWD, one of the most important lessons we have learned is that we rarely see immediate changes in CWD dynamics. This is a slow-moving disease and changes in prevalence (both increases and decreases) may not be readily apparent. Multiple repeated prevalence estimates over the long-term along with consistent management application will be necessary to evaluate patterns of change in relationship to management actions.
Lastly, severe winter conditions seen in Northwestern Colorado during the 2022-2023 winter generated many questions on potential implications for CWD dynamics in the region. Harsh winter conditions may cause more rapid mortality of infected deer in the clinical phase of disease and could reduce the number of infected animals on the landscape. Overall population reductions associated with harsh winter conditions may also affect deer/elk density on the landscape and reduce direct animal-to-animal transmission. On the other hand, prolonged concentrations of deer and elk on very limited winter ranges could facilitate increased contact as well as environmental accumulation of CWD prions (infectious agent) that could increase both direct and indirect transmission pathways.
Ultimately, the interplay of weather conditions, changing population dynamics, and changes in habitat use associated with a severe winter limit our capacity to predict how CWD prevalence might change. As we proceed with analyses to evaluate factors influencing CWD prevalence in Colorado wildlife populations, incorporating changes associated with periodic severe winters will be an important consideration.
What is Adaptive Management?
Read CPW's Chronic Wasting Disease Response Plan.
Adaptive approaches to wildlife management, or resource management, is about changing the path to achieving goals rather than changing the goals themselves.
This approach allows for flexibility to test certain ideas or hypotheses.
Through cutting edge science and innovative conservation practices, we continue to push the boundaries of science to better understand how disease affects the wildlife in Colorado.
What are CPW’s CWD Management Goals?
Reduce the spread of the disease through hunting and strategic management practices.
Work for the long-term sustainability of our herds and bring the number of animals back to our objectives.
Implement a statewide plan that will allow flexibility to meet statewide goals and hone in on local herd needs.
Herd management decisions will be based on local level input and carried out through Herd Management Plans.
Disease management is viewed as a long-term strategy.
National recommendations are working on a 10-15 year time-frame
Continue working with other state and federal agencies to increase our understanding of this disease so we can manage infected deer, elk and moose.
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Enforce laws and regulations on illegal feeding of wildlife
Colorado Parks and Wildlife 's History with CWD
Colorado has a long history and experience with chronic wasting disease (CWD) that dates to the 1960s, when the syndrome was first recognized by university scientists studying captive mule deer in research facilities west of Fort Collins.
CPW employs some of the world's leading researchers and biologists in the fight to understand and control CWD. Many aspects of CWD that were once mysteries, even into the early 2000s, are now are well-understood because of the dedication of these scientists in the understanding of this disease.
How is CPW addressing declines in mule deer other than CWD management?
Colorado Parks and Wildlife worked closely with sportspeople, landowners and community leaders to identify major areas of impacts to deer herds in Colorado.
The West Slope Mule Deer Strategy, adopted in December 2014, helps guide management decisions to help rebuild our mule deer populations. The strategy outlines 7 major tenets that are affecting our herds.
Major Weather Events* (not included in West Slope Mule Deer Strategy- but critical to wildlife management.)
We must understand as wildlife managers, and wildlife enthusiasts, that weather is one of the single most important factors in managing wildlife and habitats.
Landscape-scale habitat management to improve habitat quality.
Landscape-scale treatments are occurring across public and private land boundaries with a focus on increasing habitat carrying capacity in heavily utilized winter and transitional habitats.
Predator management where predation may be limiting deer survival. CPW is undertaking two predator management studies, one in the NW and one in the SE, to determine how population suppression can help with fawn and calf survival rates.
Protect habitat and mitigate development impacts.
CPW’s Wildlife Habitat Program uses habitat stamp money to reinvest in mitigation efforts and leverages funds.
Since 2007:
The CWHP has invested approximately $141,000,000 to protect a total of 253,000 acres.
Public access has been secured on 121,500 acres.
Conservation easements have been secured on 234,000 acres.
Reduce the impacts of highways on mule deer survival, movements and migration.
With the success of our HWY 9 Wildlife Safety project, CPW is undertaking a statewide effort with sportspeople’s organizations, CDOT, community leaders and local government to increase highway wildlife overpasses, underpasses and wildlife fencing wildlife.
Reduce the impacts of human recreation.
CPW is active in land use and land use planning efforts; we act as an advisor for these authorities to help guide their planning process. Part of those efforts include the impacts of recreation on wildlife across the state.
Regulate doe harvest and provide youth opportunity.
Harvest of female mule deer is the primary strategy CPW uses to maintain herds within the numerical population objective range established in Herd Management Plans.
Maintain a strong ungulate population and disease monitoring program with conducting applied research to improve the management of deer populations.
Through mandatory and voluntary sampling collect robust data to get a handle on geographic distribution.
Make sure CWD control is considered and included in herd management plans wherever the disease occurs.
If you have additional questions about CWD, please contact the CPW call center at (303) 297-1192.
