State of Knowledge Regarding Transmission, Spread, and Management of Chronic Wasting Disease in U.S. Captive and Free-Ranging Cervid Populations (2025)
Chapter: 8 Future Considerations
8
Future Considerations
This report describes how new knowledge about chronic wasting disease (CWD) continues to be generated through laboratory research, field studies, and management experience. The committee’s statement of task (see Box 1.2) directs the committee to draw conclusions about the state of knowledge with respect to CWD. As such, this report is a retrospective analysis of research, understanding, and practices to date, and the conclusions presented herein are based on that knowledge. A large body of research and knowledge about CWD has been generated in previous decades. Nonetheless, knowledge about specific CWD-related topics may be incomplete, may not be broadly accessible, or may be based on preliminary or unpublished research or data. As a result, the state of knowledge in those topical areas is often less mature or inconsistently shared or applied among decision makers.
CWD is a dynamic and complex emerging infectious disease, the control of which differs somewhat from other diseases that have affected free-ranging or captive cervids in the United States. Inconsistent surveillance across the United States makes it impossible to accurately determine the extent of true geographic distribution of CWD; however, ample evidence suggests the number of cases and geographic spread of the disease have increased over time. As the disease expands across North America, opportunities to manage the disease at local or regional levels becomes increasingly challenging, and new management strategies will be necessary. This final chapter synthesizes the report’s main conclusions regarding the implications of CWD transmission and spread, and the effectiveness of control activities to shift the disease trajectory toward positive outcomes. It may still be possible to modify or adopt practices to help slow transmission in many areas; however, a new commitment to sustained disease management efforts, a sense of urgency, and a call to collaborative and consistent action are necessary.
Gaps in scientific knowledge regarding different aspects of CWD challenge the adequate long-term control of the disease. Box 8.1 provides examples of such knowledge gaps. More coordinated research will be necessary to fill some of those gaps, but it is possible that many questions could be answered with using existing but inaccessible information. Frustrating for the committee was its inability to come to certain conclusions because federal and state agencies were unable to share certain kinds of information with the committee. The importance of information and data access has long been recognized as foundational to CWD management. Federal, tribal, and state agencies formed tasked forces to develop action plans for communication, scientific technical information dissemination, and data storage (e.g., Chronic Wasting Disease Task Force, 2002), but those data are still not largely available in useful and accessible formats. Much knowledge held about the disease is still implicit (i.e., in quadrant III in the knowledge matrix presented in Box 1.3), often based on undocumented or
inaccessible research and surveillance data, and shared only through, for example, discussions held in meetings following the Chatham House Rule.1
A concern of the committee is the extent to which research and management decisions are impacted by the lack of access to existing information. Decisions made with incomplete information could be fraught with uncertainty that can affect the strategic efficacy and cost-effectiveness of management decisions. The lack of information and data accessibility seems to be indicative of a larger problem—a lack of collaboration among critical interest groups. Addressing CWD is made even more challenging by significant differences in interests, values, beliefs, and behaviors resulting in a lack of a unified purpose and a lack of common goals and outcomes. Even when agreement on reducing or controlling the disease is demonstrated, acceptable strategies are dependent on individuals’ willingness to act and change behavior. Evidence-based information and knowledge need to be the foundation for determining the critical actions and programs that can prevent or reduce the transmission and spread of CWD. The inability to share information and data limits the general state of knowledge regarding CWD and is detrimental to further understanding and control of the disease.
The conclusions in this chapter are intended to inform the design of a strong action-oriented and integrated strategy to reduce the transmission and further geographic spread of the disease. They are organized in the order addressed in the report, and their order does not represent prioritization.
DRIVERS OF TRANSMISSION
CONCLUSION 1: Multiple drivers and epidemiological factors affect CWD transmission and infectivity. The precise roles, interrelationships, and relative importance of these factors are not fully understood, cannot be fully quantified, and may differ for captive and free-ranging cervid populations.
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1 The Chatham House Rule states, “When a meeting, or part thereof, is held under the Chatham House Rule, participants are free to use the information received, but neither the identity nor the affiliation of the speaker(s), nor that of any other participant may be revealed.” See https://www.chathamhouse.org/about-us/chatham-house-rule (accessed June 22, 2024).
The multiple drivers and factors affecting transmission and geographic spread of CWD and their relationships, roles, and relevance are not completely understood. Studying CWD in natural systems is difficult, and detailed understanding of many aspects of this disease derives from controlled studies conducted in either a limited number of natural or experimental hosts or in vitro. However, data derived from artificial laboratory approaches may have limited application to analogous processes occurring naturally in the environment, including transmission. For example, the infectious dose, effects of repeated exposure, CWD prion persistence in the environment, duration of incubation and host shedding of the pathogen, the molecular makeup of the prion itself, and host genetic differences influence the likelihood of transmission in a laboratory setting, but their importance has not been quantified in natural settings. Furthermore, there are numerous anthropogenic factors that likely impact CWD transmission and geographic spread, but definitive, evidence-based information regarding those is lacking.
TRANSMISSION POTENTIAL TO HUMANS AND OTHER SPECIES
CONCLUSION 2: As of this writing, no cases of CWD transmission to humans have been diagnosed or reported, nor has natural transmission to non-cervid animal species been detected.
As the prevalence and geographic distribution of CWD increase, so do the risk of exposure to other potentially susceptible species and the risk for generation of new CWD strains. Current evidence suggests that the transmission of CWD to non-cervid species is unlikely in natural scenarios, with no cases of CWD transmission to humans or other animal species having been reported. However, experimental evidence and the existence of multiple CWD strains with unknown properties do not preclude the possibility of transmission to non-cervid species. Epidemiological and experimental evidence strongly suggest that humans are resistant to CWD prion infectivity, but this barrier is not absolute and the zoonotic potential of each unique CWD strain needs to be carefully assessed. Evidence from studies incorporating experimental amplification assays and surrogate models of human susceptibility (including some—but not all—species of non-human primates and varieties of transgenic mice expressing the human prion protein) suggests that certain strains of CWD prions may have some potential to induce the human prion protein to misfold and cause disease (Kong et al., 2005; Sandberg et al., 2010; Wang et al., 2021; Race et al., 2018; Race et al., 2009b). However, those data need to be interpreted with caution, as low levels of prions, perhaps below the level of clinical relevance, may be amplified, while route of inoculation (e.g., oral versus direct injection into the brain) and strain differences may account for some of the observed variability. Experimentally, CWD prions can be made to infect multiple species that inhabit the same geographic region as cervids (e.g., pigs, raccoons, cattle, and rodents). That said, most of these transmissions were achieved by intra-cerebral inoculations (i.e., injection directly into the brain) and not natural routes of exposure. CWD prions can occur in fecal material of free-ranging carnivores such as cougars, coyotes, and crows, but the prions pass through their digestive systems without necessarily infecting them (Nichols et al., 2015; Baune et al., 2021; Inzalaco et al., 2024). Whether infection can be achieved in non-cervid species by more natural routes of exposure (e.g., ingestion) is not known, but the possibility cannot be discounted.
SPREAD OF CWD
CONCLUSION 3: The known geographic distribution of CWD is expanding. However, the distribution is incompletely understood and likely underestimated. Inconsistent surveillance has compromised knowledge about changes in CWD distribution over time in the United States.
At the time of this writing, CWD has been reported in 35 states in the United States. However, the timeline(s) for its geographic spread cannot be inferred reliably based only on the chronology of first detections in a region. Surveillance and monitoring present unique challenges among captive and free-ranging herds. Organized surveillance was virtually absent in the United States prior to 1997, and records from subsequent surveillance, outbreak investigations, reporting, and documentation of human-assisted translocation of cervids or cervid parts are incomplete. CWD surveillance in both captive and free-ranging cervids has improved generally since 2002, although
the data and details of surveillance efforts were largely unavailable to this study committee and are, apparently, not readily available to either the broader scientific community or the public. This lack of transparency impedes the general understanding of CWD, perspectives about historical and current extent of CWD, the effectiveness of surveillance activities, public trust in agency management, and ultimately the control of CWD in both free-ranging and captive cervids. These impediments are compounded by the fact that current surveillance practices and participation remain inconsistently applied on a national scale, and thus CWD distribution is likely underestimated.
CONCLUSION 4: Natural movement of infected cervids and other epidemiological factors are responsible for the local distribution of CWD. Human-mediated movement of infected cervids (i.e., transport of live, dead, captive, or free-ranging cervids) and infected cervid products for commerce, recreation, conservation, and other purposes increases the likelihood of CWD spreading to new geographic areas in unpredictable ways.
Outbreaks of CWD rely on the introduction of infectious prions to new localities. The spread to these localities is often facilitated by moving infectious hosts, either live cervids or cervid carcasses, and potentially by moving other cervid products containing CWD prions (e.g., antler velvet and urine), across long distances. The distances between known and some “new” foci are difficult to account for based solely on observed natural cervid movements. Free-ranging cervids may move extensively across their home ranges, causing the disease to radiate from its point of introduction. The commercial transport of captive cervids has unwittingly moved the disease across state and even international boundaries. The result of undocumented anthropogenic movement of CWD is less predictable than natural mechanisms for spreading the disease. While numerous bans have been implemented prohibiting the movement of select portions of hunter-harvested cervids across jurisdictions through state and provincial carcass import regulations,2 compliance with these regulations is not well studied. Given the risk of environmental transmission and the role of CWD-infected cervids in environmental contamination, efforts to reduce the movement of infectious cervids or cervid parts will reduce the risk of direct or indirect transmission to new hosts or landscapes. Once a new locality has been contaminated with CWD, human behavior at local scales (e.g., improper disposal of carcass parts, use of attractants or bait to encourage aggregation of cervids, handling of CWD-positive cervids) may increase the spread of the disease. Furthermore, the natural movement ecology of cervid populations may foster increased direct and indirect transmission risk among deer family groups and those using spatially overlapping environments.
DIAGNOSTIC METHODS
CONCLUSION 5: Official U.S. Department of Agriculture (USDA) postmortem CWD diagnostic approaches are useful for disease surveillance in both free-ranging and captive cervids. Newer, as yet unapproved, detection approaches may have more wide-ranging applications, including live-animal testing and screening of cervid byproducts, environmental surfaces, and other relevant materials.
Since the early 2000s, CWD detection and surveillance has largely relied on standardized immunohistochemistry (IHC) or enzyme-linked immunosorbent assay (ELISA) protocols for the detection of the misfolded prion protein in lymphoid and neural tissues—predominantly in tissues collected postmortem. These approaches have been used by state, federal, and tribal agencies to identify newly infected free-ranging and captive cervid herds and estimate disease prevalence either passively during routine sampling or actively during depopulation, for example. These methods, although accurate, have not been widely applied for live-animal testing and cannot be used in surveilling environmental or biological components (e.g., soil, plants, insects, or bodily waste) that may act as sources of CWD transmission.
At roughly the same time that these “conventional” approaches were first approved for widescale CWD testing across North America, development of amplification-based tests for prion disorders was underway, initially through the protein misfolding cyclic amplification (PMCA) assay and eventually the real-time quaking-induced conversion (RT-QuIC) assay. These amplification assays have demonstrated arguably higher levels of sensitivity
than their conventional counterparts, allowing use of samples collected from live cervids, and have proven useful in evaluating a range of matrices including bodily fluids and environmental samples that are untestable by IHC and ELISA. Despite their potentially higher levels of sensitivity and utility in assessing non-traditional samples, these amplification assays require further validation and interlaboratory standardization and have not yet been approved by regulating bodies.
New knowledge and improved diagnostic and detection methods to accurately surveil potential environmental contamination and to monitor changes and emergence of new strains are especially needed to confront challenges where the disease has become established.
CONTROL
CONCLUSION 6: Well-founded epidemiological principles inform strategies for CWD prevention or control in both captive and free-ranging cervids, beginning with effective early and ongoing surveillance and followed by timely, aggressive, sustained local response upon the presence of CWD being discovered. Although imperfect, methods based on those principles can reduce or prevent large increases in prevalence and slow the spread of CWD when properly applied.
Although CWD has some unique characteristics regarding transmission and spread, it, nevertheless, follows the same epidemiological principles as other contagious infectious diseases. The traditional epidemiologic triad model holds that infectious diseases result from the interactions among an agent, host, and environment. Transmission occurs when the agent (prion) leaves the host/reservoir (CWD-infected cervids) through a portal of exit, is conveyed by some mode of transmission (direct or indirect), and enters through a portal of entry (oral, etc.) to infect a susceptible host. This sequence is referred to as the chain of infection. The components of the chain regarding CWD have been described throughout this report. All infectious diseases, whether the agent is a virus, bacterium, fungus, parasite, or prion or whether the disease involves humans or animals, can be described and explained by this foundational principle (Dicker, 1992).
Knowledge of the portal of exit and entry and the mode of transmission provides a basis for determining appropriate control measures. In general, control measures are usually directed against the segment of the infection chain that is most susceptible to intervention. For bovine spongiform encephalopathy (BSE), another transmissible spongiform encephalopathy (TSE), epidemic was mostly limited and stopped by breaking the transmission cycle by removing BSE prions from animal feed, thus eliminating the portal of entry to a new host. For scrapie the control strategy focuses on controlling environmental contamination but especially strengthening the resistance of a new host, via genetic selection, and breaking the cycle of new infections.
Box 6.4 lists potential methods and strategies being used to help control CWD. All the tools are based on ways to break the chain of infection and interrupt transmission and spread of the disease. The tools can be used singularly or in combination and are often used based on available resources, levels of endemicity, farmed versus free-ranging populations, host variability, environmental issues, etc. Understanding and implementing the use of these tools can be improved through further studies and experiences; however, the basic epidemiologic principle, cycle of infection, is still the time-proven foundation that can guide interventions. The state of knowledge on many of these factors can be expanded to improve and inform new strategies; however, the proper and sustained use of these tools and understanding how they might break the infection chain allows us to use current methods, that are still valid and available, to control and prevent CWD as new strategies emerge and are validated.
As reflected in this report, there is sufficient knowledge to help slow the spread and reduce transmission of CWD while new scientific knowledge, advances, and evidence-based control strategies are developed. Current understanding, albeit incomplete, is sufficient to inform comprehensive control strategies and to prioritize needs for further investigation. For example, the existing knowledge that infected host cervids, their residual secretions and excretions, and their carcasses are sources of infectivity can inform measures for CWD control. Such control measures include risk-based and targeted culling and increased hunting pressure on infected herds to control prevalence, baiting and feeding restrictions to reduce cervid aggregation, appropriate carcass handling, and compulsory surveillance and commercial movement regulations to curtail spread (see Box 6.4
and Chapters 4 and 6). In contrast, the potential contributions of non-host sources of CWD prions (e.g., contaminated feed) to transmission and geographic spread are not as well understood and have yet to be considered fully in the context of control. Thorough epidemiologic analyses of new infections are warranted to improve understanding of risk factors and improve disease prevention and biosecurity measures. Collaborative efforts to understand the collective portfolio of evidence and to convert existing but inaccessible or anecdotal information into accessible and actionable information will enhance the collective ability to blunt the effects of the disease in the short term while research continues to develop longer-term control solutions.
CONCLUSION 7: Differing philosophies and approaches to CWD management adopted by agricultural and wildlife management authorities at different levels of government impact the effective control of CWD in the United States.
The diverse viewpoints of interested parties and the differences in authorities in local, state, tribal, and federal jurisdictions complicate efforts to control CWD. The epidemiological characteristics of CWD, the uncertainties regarding its transmission and spread, the long lead times before animal mortality is observed, and a lack of demonstrated human harm from the disease makes crafting and justifying control policies in response to CWD challenging. Furthermore, CWD is managed by local, state, tribal, and federal officials that operate under different authorities, jurisdictions, regulations, guidelines, social pressures, and management strategies, often with inadequate resources. The result has been a patchwork of prevention and control strategies that are unevenly and inconsistently adopted, implemented, and evaluated.
Management objectives of responsible agencies differ, and therefore the approaches to controlling CWD are likely to remain different. State and federal agricultural agencies are largely responsible for managing captive cervids (generally considered livestock), primarily for the economic benefit of producers and for meeting market demand for cervids and their products. The goals of state, tribal, and federal wildlife management agencies often focus on maximizing recreational, economic, and societal values associated with free-ranging cervids. For example, reducing deer populations at a local or regional level to limit transmission can directly conflict with hunter and wildlife enthusiast preferences for seeing greater numbers of cervids on the landscape. Tribal agencies may have the additional challenges of balancing cultural and traditional values, food sovereignty, and a subsistence economy with wildlife management priorities, while also having limited agency capacity and high administrative burden in acquiring federal funding and grant management.
Given current strategies and management practices, it cannot be expected that the disease can be eradicated in areas where it is already well established, but prevalence could be controlled and spread can be slowed even as additional control tools can be developed, validated, and implemented. The worst-case scenario is that the disease will spread across the entirety of the country, wherever cervids are present. A better understanding of the underlying genetics of disease resistance, coordinated and complementary control strategies, and the development of and access to diagnostic approaches are important considerations for overcoming the present impediments to CWD control. In addition, it will take honest, concerted, collaborative, patient, dedicated, and consistent long-term effort from numerous agencies and interested and affected parties to identify and weigh conflicting scientific, social, and economic priorities, and come to agreement on appropriate solutions for protecting both captive and free-ranging populations. Greatest success is likely when prevention and management plans are introduced before disease is detected, providing opportunity to slow the spread when the prevalence is low. Supporting further research into new effective interventions and better utilization and implementation of known control strategies would inform future adaptive management decisions for free-ranging populations.
CONCLUSION 8: Prevention is key to controlling the spread of CWD given that existing tools and technologies make eradication of CWD in captive or free-ranging cervid populations, once established, improbable. Ongoing and effective surveillance programs can facilitate early detection and response.
Managing CWD is complex because (1) surveillance in free-ranging cervids is constrained; (2) environmental contamination and its contribution to indirect transmission are persistent; (3) early diagnosis of infection in live
cervids is challenging; (4) vaccines against or therapeutics to treat CWD are lacking; and (5) recruiting interested and affected parties to participate in control is difficult. Once CWD is established in a free-ranging cervid population, CWD is unlikely to be eradicated with existing scientific methodologies, technologies, and current management and surveillance practices. However, there are limited examples where early detection of CWD and prompt, aggressive response resulted in the local apparent eradication of the disease and the prevention of spread to nearby areas (see Chapter 6 and Box 7.1). Ongoing and effective surveillance programs allow early detection of CWD and sustained adaptive management to respond to changing conditions. Strategies that prevent the introduction of CWD to a region or captive facility are important in controlling further spread of the disease, but ongoing surveillance once controlled in a location is crucial to detect disease re-emergence.
Once CWD has become established in an area, successful management and control strategies may keep CWD prevalence at low levels. Maintaining low CWD prevalence may limit the buildup and overall contribution of environmental contamination to ongoing transmission, but it is yet unclear how long low prevalence levels can be suppressed with active management. Environmental contamination is not homogeneous across the landscape; the persistence of CWD prions is dependent on soil type and potentially other factors such as weather, vegetation, heterogeneities in the landscape, and sympatric animal species. This complicates the development and implementation of environmental contamination mitigation strategies in captive cervid settings or specific habitat manipulations for free-ranging cervids. Presently, there are no feasible environmental treatments or habitat modifications that effectively limit or eliminate prions.
Quickly identifying CWD-infected captive herds and removing them from the landscape are likely important in controlling disease spread. Infection of captive cervid herds can be limited with strong biosecurity and preventive management; however, these cervids are still at risk, particularly in areas where the disease occurs among free-ranging cervids. It is reasonable to expect that the USDA CWD HCP has contributed to limiting the interstate spread of CWD, but, in its current form, the program may lack the scope, resources, and jurisdictional authority to fully mitigate the risks of CWD in captive cervids. Hence, an in-depth epidemiological analysis of CWD-infected herds, including those enrolled and not enrolled in the HCP, would be beneficial to better understand key risk factors, program reductions to CWD risk, and necessary improvements in disease prevention and biosecurity.
CONCLUSION 9: Genetic selection, vaccines, environmental decontamination, and therapeutic options are being investigated as tools for CWD control but need further inquiry and review. Although none of these approaches can, at present, replace existing forms of management and control, in the future they may, in combination with current methods, reduce CWD on the landscape.
Genetic resistance, vaccines, and therapeutic options have garnered hope among some as solutions for CWD control. At this time, there are insufficient data and validation to determine their effectiveness. As discussed in 6, studies using selective breeding, incorporating both PRNP and genome-wide associations with susceptibility, as a management tool in the control of CWD in captive white-tailed deer and elk herds are in their early stages. The impacts of different rates and lengths of exposure in these herds, as well as exposure to different CWD strains, have not been determined, which may limit utility of selective breeding for managing CWD in captive cervids, particularly newly developed strains of CWD that might preferentially infect cervids with PRNP genotypes presently considered less susceptible to infection. The downstream effects of infected animals with extended incubation times shedding infectious prions in the environment for prolonged periods have also not been addressed. The applications for genetics in managing CWD in free-ranging populations have not been described or addressed. Longitudinal studies in both captive and free-ranging populations would facilitate a better understanding of genetics on relative susceptibility to prion infection and prion shedding, as well as applicability in captive or free-ranging conditions.
Vaccines, environmental decontamination, and therapeutics have also been investigated. The results of past and ongoing vaccine development efforts have been inconsistent. Without better knowledge of cervid and prion biology, these strategies may not be optimally utilized. Barriers to implementation remain, especially in free-ranging cervids, including the difficulties associated with vaccine delivery, the potential uncertainties in CWD prion shedding in vaccinated, cervids, and protection against a range of different CWD strains. Finally, environmental decontamination
protocols and therapeutic options for CWD and other livestock prion disorders are practically non-existent. The development and implementation of environmental contamination mitigation strategies in captive cervid settings or specific habitat manipulations for free-ranging cervids is challenging because of heterogeneities in environmental contamination within landscapes. Although there is limited evidence for efficacy in reversing the course of protein misfolding or reducing infectivity in biological samples, there is no evidence of whether this is effective in cervids or in the environment. While each of these avenues may be important in CWD management in the future, current strategies focusing on active surveillance and regulations covering the movement of cervids and their byproducts will help slow the transmission and spread until more effective management options are developed, validated, and implemented.
SOCIAL AND JURISDICTIONAL FACTORS
CONCLUSION 10: Human behaviors can influence the transmission, spread, and consequences of CWD. Interest groups hold diverse viewpoints regarding the seriousness of CWD and about its spread, prevention, and control; their decisions may not always be informed or influenced by the best available science.
CWD touches the lives, livelihoods, and enjoyment of many interested and affected parties. Numerous and diverse organizations, government agencies, interested and affected parties, and disciplines with differing points of view, incentives, interests, values, policies, and authorities have concerns regarding CWD. The diversity of views can make it difficult to reach consensus when interpreting information and deciding disease management strategies. The different views, cultures, relationships, levels of trust, and senses of urgency among groups and individuals are often in opposition and can impact control of the disease. The lack of access to data and information can contribute to the lack of trust, coordination, and cooperation among interested and affected parties. Chapter 5 describes some of the evidence of human actions that may contribute to the geographic spread of CWD, and Chapter 7 describes some of the drivers for those actions. For example, the transport of infected cervids or carcasses may be responsible for disease spread. There are agencies, interest groups, and individuals that make decisions to avoid transporting potentially infected cervids and carcasses to slow the spread of CWD. However, there are also groups and individuals whose livelihoods may depend on transporting cervids, who may not have the resources to change their behaviors or actions, whose way of life may be threatened by changing rules, or who may be unaware of the CWD-related risks because of either a lack of information or because of the easy availability of misinformation (see Box 8.2). State and local jurisdictions are often more reactive to social, political, and economic forces than scientific evidence, and such decisions and actions may thwart efforts to slow the spread of CWD.
As concluded earlier, the multiple viewpoints and differences in authorities, available resources, and disease management practices across jurisdictions addressing CWD result in inconsistent and sometimes incompatible management. Lack of mechanisms for communication and coordination around data collection and information sharing across jurisdictions precludes an evaluation of control measures and their efficacy. Without coordination among individual jurisdictions, the knowledge held by individual jurisdictions cannot be leveraged. For example,
logic dictates that the USDA HCP may have had a positive impact on limiting the interstate spread of CWD. However, the committee has no access to any existing data that might quantify those impacts, and CWD continues to be identified in HCP herds. Any data collected would likely be at the state or local levels, and there is little to no ability to get or share epidemiological information regarding CWD in captive HCP or non-HCP herds. The HCP provides an important framework for CWD management in captive herds that could be refined and expanded.
While management of CWD is necessarily local and needs to be responsive to unique local conditions, larger-scale coordination also seems necessary because CWD does not respect jurisdictional boundaries. Collaborative strategies are needed to manage the disease as well as provide the flexibility needed by officials. Scientific challenges are often compounded by social, political, and economic challenges.
Translation of scientific knowledge regarding CWD into decision-making requires making full use of knowledge and understanding of CWD gained through collaborative and coordinated open sharing across disciplines, government and private organizations, and political levels. Collaboration and coordination across multiple and differing partners are critical to mitigate the ongoing negative impacts of the disease on population levels; minimize socioeconomic impacts of the disease; and launch effective, sustainable interventions and assessments of management alternatives. Sociologists, economists, behaviorists, anthropologists, and others could be included in studying and understanding the impact and spread of CWD to appreciate its impact on local populations and communities.
ECONOMIC ANALYSES
CONCLUSION 11: Existing data gaps make CWD-related economic measurements and analyses difficult to quantify. These deficiencies can result in a lack of appreciation of the full impact of the disease and in the inability to evaluate and compare the direct and indirect costs and benefits of various management strategies.
There is sufficient evidence to indicate that CWD is a costly disease and that it is becoming more costly and consequential as it continues to spread and infect more populations. However, the economics of CWD are not well understood, and this is detrimental to an in-depth understanding of the impacts of the disease and the need for its control. The inability to generate economic impact analyses leads to the inability to calculate cost-benefit analyses on CWD prevention, reduction, and control programs. Expenses associated with CWD management represent economic vulnerabilities for the federal, tribal, state, and local entities with CWD-related authorities and responsibilities that may be unequipped or underequipped to meet the current challenges of CWD, and resources currently available may be insufficient to address CWD as it continues to spread. Tribal wildlife management entities are further constrained by the lack of resources and staff and levels of administrative burden associated with the complicated processes for transfer of federal funding and grant management.
Although some data regarding state and federal costs and expenditures are available, the full economic burden or impact of CWD on most states cannot be quantified. Costs and benefits of CWD management options will depend on multiple variables including the current and predicted populations of both captive and free-ranging cervids, local economies, and a range of human dimensions. At present most jurisdictions can only produce rough estimates of the numbers and locations of free-ranging cervids and herds. Analyses of captive and free-ranging population levels in a wide variety of locales, and in concert with robust CWD surveillance programs, would support cost-benefit analyses of localized CWD management activities. Estimates of opportunity cost functions allow the prediction of future consequences of additional captive or free-ranging herds becoming infected with CWD. The lack of accurate and up-to-date economic information may result in some entities and individuals undervaluing the impacts of CWD and diminish any sense of urgency to act on CWD.
CONCLUDING THOUGHTS
It is known that CWD results in increasing mortalities in cervids, negatively affecting individual cervids and, at sufficiently high infection prevalence, their population growth rates (particularly in deer) over time. Localized impacts of CWD may differ depending on a variety of ecological and human factors. The potential social and ecological ramifications of the increasing spread of CWD are severe and could include large-scale economic
losses to affected states and to the commercial efforts related to captive cervids. CWD creates a more challenging environment to rear captive herds, including direct and indirect economic losses associated with increased regulations, guidance, and policies. It also results in substantial costs in money and time for local, state, tribal, and federal government agencies.
CWD is likely to be a part of the North American landscape for the foreseeable future. Infected cervids have a long incubation period. Through much of the incubation period, including when cervids show no outward signs of the disease, prions are shed to the environment and become a persistent threat. The considerable knowledge about CWD gained in more than 40 years can be drawn upon, in conjunction with the sustained and collaborative commitment of resources and effort by all entities with an interest in CWD and cervid health, to slow the spread of the disease in the near term. A sustained collaborative effort over decades using the accumulation of the credible CWD-related scientific knowledge (e.g., what is known and unknown, what is important and not important) is the foundation for long-term effort to change the trajectory of CWD in free-ranging and captive cervids.
The nature of science in any area is that it evolves and is refined as more is learned, confirmed, and validated. As such, the state of knowledge is still evolving, with healthy scientific debate occurring over investigative results that sometimes appear contradictory. And although CWD has been researched for decades, there are many investigations and data that have yet to be documented, validated, and made readily available to those trying to understand or make decisions related to CWD management. There are gaps in knowledge related to multiple aspects of CWD and its epidemiological and biological complexity, and the diversity and competing views of various interested and affected parties make CWD challenging to address and control. However, the ability to adopt and implement strategies already known and scientifically supported can result in a productive, cost-effective set of interventions capable of slowing the transmission and spread. Science, collaborative research, and experience continue to provide new knowledge and understanding of CWD in free-ranging and captive cervids. Further exploration of how to apply this knowledge, particularly to free-ranging populations, would improve management decisions aimed at altering the trajectory of CWD in the United States and perhaps beyond.
