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Leslie Matrix Population Model. Post-breeding, age-structured, female-dominated 18x18 Leslie Matrix model of white-tailed deer population on Deer Creek drainage SW of Glenrock, WY (2003–2010) that was located within the chronic wasting disease (CWD) endemic area. nt represents the number of deer in each age class by CWD-status ((-) = PrPCWD not detected, (+) = PrPCWD detected). represents estimated survival by age class, i, and CWD-status (- or +), is the estimated fecundity rate and is the age-specific CWD incidence rate.
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Chronic wasting disease (CWD) is an invariably fatal transmissible spongiform encephalopathy of white-tailed deer, mule deer, elk, and moose. Despite a 100% fatality rate, areas of high prevalence, and increasingly expanding geographic endemic areas, little is known about the population-level effects of CWD in deer. To investigate these effects, we...
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... vital rates were estimated separately for CWD-negative and CWD-positive deer except fecundity, which did not differ by CWD-status. The 18 x 18 transition matrix, A, represented the estimated demographic rates of the study population with both CWD-negative and CWD-positive females, and the transition between them due to infec- tion, represented (Fig 1). We calculated the population growth rate as the dominant eigenvalue, λ 1 [35]. ...
Citations
... Although a causal link was not the focus of this study, a decline of agency trust and risk perception should be expected if the public anticipates mass mortality or population crashes within a few years of CWD detection, a narrative constructed by poor messaging and oscillating media interest. Several studies since 2004 have demonstrated serious population impacts under high infection rates (e.g., Miller et al. 2008, Edmunds et al. 2016, DeVivo et al. 2017. However, infection rates reported in such studies are typically reached decades after the first detection, effects may be imperceptible for several years following early detection, and population decline is likely at 1 end of a wide spectrum of possible impacts. ...
Using a pre−post chronic wasting disease (CWD) natural experiment, we compared deer hunters' perceived trust in the North Dakota Game and Fish (NDGF) Department and perceived CWD risks to wildlife and humans before and after the discovery of the disease in the state. We obtained data from 2 mail surveys. One study was conducted in 2004 (n = 855, response rate = 43%) when CWD had not been detected in North Dakota; the second was conducted in 2021 (n = 3,242, response rate = 29%) after the disease was known to exist in the state. We hypothesized that when compared to the 2021 hunters, the 2004 hunters would (1) be more trusting of the NDGF's management of CWD, (2) perceive more risk to deer, and (3) perceive more risk to humans. All 3 hypotheses were supported. Hunters expressed greater trust in NDGF information regarding CWD (Cohen's d = 0.173, P < 0.001), higher levels of risk to deer (d = 0.433, P < 0.001), and higher levels of risk to humans in 2004 than in 2021 (d = 0.730, P < 0.001).
... We capitalized on cause-specific mortality data from mule deer (Odocoileus hemionus) fitted with GPS collars to investigate how movement behavior and habitat use may be influenced by infection with a chronic disease. Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy that affects members of the Cervidae family (Miller et al., 2000;Williams & Young, 1980) with the potential for population-level consequences (DeVivo et al., 2017;Edmunds et al., 2016). The impacts of CWD may be more severe in certain species and environments, such as less productive semiarid systems (Foley et al., 2016). ...
Integrating host movement and pathogen data is a central issue in wildlife disease ecology that will allow for a better understanding of disease transmission. We examined how adult female mule deer (Odocoileus hemionus) responded behaviorally to infection with chronic wasting disease (CWD). We compared movement and habitat use of CWD‐infected deer (n = 18) to those that succumbed to starvation (and were CWD‐negative by ELISA and IHC; n = 8) and others in which CWD was not detected (n = 111, including animals that survived the duration of the study) using GPS collar data from two distinct populations collared in central Wyoming, USA during 2018–2022. CWD and predation were the leading causes of mortality during our study (32/91 deaths attributed to CWD and 27/91 deaths attributed to predation). Deer infected with CWD moved slower and used lower elevation areas closer to rivers in the months preceding death compared with uninfected deer that did not succumb to starvation. Although CWD‐infected deer and those that died of starvation moved at similar speeds during the final months of life, CWD‐infected deer used areas closer to streams with less herbaceous biomass than starved deer. These behavioral differences may allow for the development of predictive models of disease status from movement data, which will be useful to supplement field and laboratory diagnostics or when mortalities cannot be quickly retrieved to assess cause‐specific mortality. Furthermore, identifying individuals who are sick before predation events could help to assess the extent to which disease mortality is compensatory with predation. Finally, infected animals began to slow down around 4 months prior to death from CWD. Our approach for detecting the timing of infection‐induced shifts in movement behavior may be useful in application to other disease systems to better understand the response of wildlife to infectious disease.
... The disease is fatal and there is currently no treatment (Miller & Williams, 2004). If left unchecked, models predict CWD will lead to long-term population declines of multiple species and possibly local extinction (Edmunds et al., 2016;Miller & Williams, 2004). Chronic wasting disease is difficult to eliminate from wild populations since the amount of infectious prions in the environment increases with the number of infectious animals (Gross & Miller, 2001;Manjerovic et al., 2014). ...
Chronic wasting disease (CWD) can spread among cervids by direct and indirect transmission, the former being more likely in emerging areas. Identifying subpopulations allows the delineation of focal areas to target for intervention. We aimed to assess the population structure of white‐tailed deer (Odocoileus virginianus) in the northeastern United States at a regional scale to inform managers regarding gene flow throughout the region. We genotyped 10 microsatellites in 5701 wild deer samples from Maryland, New York, Ohio, Pennsylvania, and Virginia. We evaluated the distribution of genetic variability through spatial principal component analysis and inferred genetic structure using non‐spatial and spatial Bayesian clustering algorithms (BCAs). We simulated populations representing each inferred wild cluster, wild deer in each state and each physiographic province, total wild population, and a captive population. We conducted genetic assignment tests using these potential sources, calculating the probability of samples being correctly assigned to their origin. Non‐spatial BCA identified two clusters across the region, while spatial BCA suggested a maximum of nine clusters. Assignment tests correctly placed deer into captive or wild origin in most cases (94%), as previously reported, but performance varied when assigning wild deer to more specific origins. Assignments to clusters inferred via non‐spatial BCA performed well, but efficiency was greatly reduced when assigning samples to clusters inferred via spatial BCA. Differences between spatial BCA clusters are not strong enough to make assignment tests a reliable method for inferring the geographic origin of deer using 10 microsatellites. However, the genetic distinction between clusters may indicate natural and anthropogenic barriers of interest for management.
... The persistent prevalence of CWD has had detrimental effects on the health and ecology of cervids. The long-term negative effects on deer health were linked to a decreased survival rate and low population growth as CWD-positive animals were more likely to die than their CWD-negative animals [9,10,69]. For example [70], discovered a lower probability of fawning among infected female mule deer compared to the healthy deer in Colorado. ...
With 100% fatality and no cure, chronic wasting disease (CWD) has infected cervids in multiple regions, including the United States, Canada, Europe, and South Korea. Despite the rapid growth of literature on CWD, the full scope of its ecological, social, and economic impacts and the most effective and socially acceptable management strategies to mitigate the disease are unclear. Of 3,008 initially identified published peer-reviewed papers, 134 were included in a final systematic literature review to better understand CWD transmission patterns, impacts, and the effectiveness of management interventions. The number of publications on CWD has increased steadily since 2000 with an average of six papers per year. Most papers were related to CWD prevalence (39%), human behavior (33%), CWD impacts (31%), and management interventions (16%). Environmental factors such as soil, water, and plants were identified as the most common transmission sources, with a higher prevalence rate among adult male cervids than females. Hunters showed a higher risk perception and were more likely to change hunting behavior due to CWD detection than non-hunters. Ecological impacts included the decreased survival rate accompanied by lower population growth, eventually leading to the decline of cervid populations. Culling was found to be an effective and widely implemented management strategy across countries, although it often was associated with public resistance. Despite potentially high negative economic impacts anticipated due to CWD, studies on this subject were limited. Sustained surveillance, ongoing research, and engagement of affected stakeholders will be essential for future disease control and management.
... Infected individuals gradually accumulate an abnormal isoform of cellular prion proteins and die at advanced stages of the disease (Güere et al., 2020). Population level effects of the | 3 of 14 disease have been observed in white-tailed deer (Odocoileus virginianus) and mule deer (Odocoileus hemionus) (DeVivo et al., 2017;Edmunds et al., 2016). Until recently, the disease was limited to North America and the Republic of Korea, but in 2016 it was discovered in Eurasian wild reindeer (Rangifer tarandus) and moose in Norway (Benestad et al., 2016). ...
... tive impact on the future growth rate of the population and possibly cause a decrease in population size(DeVivo et al., 2017;Edmunds et al., 2016;Haley & Hoover, 2015). The risk of transmission of CWD to other species of cervids or domestic animals may also be pres-ent (Moazami-Goudarzi et al., 2021). ...
Harvesting and culling are methods used to monitor and manage wildlife diseases. An important consequence of these practices is a change in the genetic dynamics of affected populations that may threaten their long‐term viability. The effective population size (Ne) is a fundamental parameter for describing such changes as it determines the amount of genetic drift in a population. Here, we estimate Ne of a harvested wild reindeer population in Norway. Then we use simulations to investigate the genetic consequences of management efforts for handling a recent spread of chronic wasting disease, including increased adult male harvest and population decimation. The Ne/N ratio in this population was found to be 0.124 at the end of the study period, compared to 0.239 in the preceding 14 years period. The difference was caused by increased harvest rates with a high proportion of adult males (older than 2.5 years) being shot (15.2% in 2005–2018 and 44.8% in 2021). Increased harvest rates decreased Ne in the simulations, but less sex biased harvest strategies had a lower negative impact. For harvest strategies that yield stable population dynamics, shifting the harvest from calves to adult males and females increased Ne. Population decimation always resulted in decreased genetic variation in the population, with higher loss of heterozygosity and rare alleles with more severe decimation or longer periods of low population size. A very high proportion of males in the harvest had the most severe consequences for the loss of genetic variation. This study clearly shows how the effects of harvest strategies and changes in population size interact to determine the genetic drift of a managed population. The long‐term genetic viability of wildlife populations subject to a disease will also depend on population impacts of the disease and how these interact with management actions.
... Many states within the U.S. report apparent prevalence of CWD in male cervids as 2-to 3-times greater than prevalence in females within a population (Miller and Conner, 2005;DeVivo et al., 2017;Samuel and Storm, 2016; but see Edmunds et al. 2016). By accounting for differences in monthly contact rates within and between different sexes of deer in the modeled population and applying a correction factor to males for indirect and direct CWD transmission, our goal was to reproduce these sex-specific trends in prevalence of CWD. ...
... Researchers and wildlife managers have estimated that, at some point, indirect transmission becomes more important than direct transmission on CWD dynamics in free-ranging cervid populations endemic with the disease. This estimate stems from the ideas that 1) CWD reduces population size and deer density over time, which reduces the number of contacts made and, thus, direct transmission events among deer, and 2) prions accumulate in the soil within affected areas over time, which increase the probability of local deer becoming infected indirectly through the environment (Edmunds et al., 2016;DeVivo et al., 2017). The sensitivity analysis we performed on the IBM supports this transition of influence between transmission modes and suggests that the transition occurs between 15 and 20 years post initial introduction of CWD. ...
Chronic wasting disease (CWD) is an infectious prion disease that infects members of the Cervidae family (i.e., deer) resulting in widespread ecological, economic, and recreational ramifications. We introduce a spatially explicit individual-based model (IBM) that integrates individual deer movement and behavior with population and disease dynamics to forecast CWD in populations of free-ranging white-tailed deer (Odocoileus virginianus). We use a Susceptible-Exposed-Infectious-Dead (S-E-I-D) epidemiological framework to explore spatiotemporal dynamics of CWD within an agriculturally dominated area in Michigan, USA. The IBM results closely mimicked documented short-and long-term dynamics of white-tailed deer populations and CWD in the Midwestern, USA. We applied pattern-oriented modeling using annual apparent CWD prevalence rates reported by Midwestern state wildlife agencies to validate the disease model. The introduction of a single infected deer to the modeled landscape (93 km 2) led to an outbreak of CWD in 100 out of 350 model simulations (29 %); prevalence never exceeded 1.47 % for repetitions where the outbreak ended. For the 100 simulations where disease persisted, the deer population declined by 87 % by year 50 following initial introduction of CWD. Mean (±SD) prevalence after 5, 10, 25, and 50 years was 1.1 % (±1.0 %), 3.4 % (±3.3 %), 46.5 % (±18.8 %), and 51.8 % (±18.1 %), respectively, which highly correlated (r = 0.99) with annual CWD prevalence reported in Wisconsin white-tailed deer populations for years 1-21 post initial detection. Combined with a global sensitivity analysis, the IBM indicated that prevalence of CWD at year 20 was most sensitive to harvest rate of yearling and adult female deer and least sensitive to prion shedding rate, prion half-life, and deer group numbers, indicating that deer population parameters were more influential than disease parameters on CWD dynamics. Our IBM serves as a tool to explore and better understand indirect and direct transmission of CWD within free-ranging cervid populations. Users of this model can adjust parameter values to explore how interactions among individual deer and between deer and their environment affect CWD dynamics. This IBM also serves as a framework for applying and assessing spatially and temporally explicit management scenarios.
... Chronic wasting disease (CWD) is a transmissible neurological disease among Cervids that is caused by prion mutations (Edmunds et al., 2016;Haley & Hoover, 2015;Saunders et al., 2012). Abnormal behavior, emaciation, and death occur in all CWD infected animals (Williams et al., 2002). ...
... It has been detected in free-ranging cervids in 29 U.S. states and three Canadian provinces in North America, as well as Finland, Norway, South Korea, and Sweden. The disease is of particular concern due to potential long-term demographic impacts to infected cervid populations [Edmunds et al. (2016), DeVivo et al. (2017] and the economic importance of deer hunting in the USA, which generated over 27 billion dollars in 2016 (Southwick-Associates 2018). Generally, wildlife agencies lead efforts to conduct all disease surveillance and management activities in their jurisdiction. ...
A two-parameter model and a Bayesian statistical framework are proposed for estimating prevalence and determining sample size requirements for detecting disease in free-ranging wildlife. Current approaches tend to rely on random (ideal) sampling conditions or on highly specialized computer simulations. The model-based approach presented here can accommodate a range of different sampling schemes and allows for complications that arise in the free-ranging wildlife setting including the natural clustering of individuals on the landscape and correlation in disease status from transmission among individuals. Correlation between individuals and the sampling scheme have important consequences for the sample size requirements. Specifically, high within cluster correlations in disease status can reduce sample size requirements by reducing the effective population size. However, disproportionate sampling of small subsets of subjects from the greater target population, combined with high correlation of disease status, tends to inflate sample size requirements, because it increases the likelihood of sampling multiple animals within the same highly correlated clusters, resulting in little additional information gleaned from those samples. Our results are consistent with those generated using both previously established approaches and extend their ability to adapt to additional biological, epidemiological, or societal sampling complications specific to wildlife health.
... CWD is highly prevalent in North America and has been detected in 29 states of the USA and 4 Canadian provinces [21]. High levels of transmission occur in high prevalence areas that have resulted in a significant decline in wild cervid populations, such as white-tailed deer and mule deer [22,23]. CWD has recently been described in Europe [24] with cases identified in free-ranging reindeer, moose and red deer in Finland, Norway and Sweden, collectively. ...
Chronic wasting disease is a fatal prion condition of cervids such as deer, elk, moose and reindeer. Secretion and excretion of prion infectivity from North American cervids with this condition causes environmental contamination and subsequent efficient lateral transmission in free-ranging and farmed cervids. Variants of cervid PrP exist that affect host susceptibility to chronic wasting disease. Cervid breeding programmes aimed at increasing the frequency of PrP variants associated with resistance to chronic wasting disease may reduce the burden of this condition in animals and lower the risk of zoonotic disease. This strategy requires a relatively rapid and economically viable model system to characterise and support selection of prion disease-modifying cervid PrP variants. Here we generated cervid PrP transgenic Drosophila to fulfil this purpose. We have generated Drosophila transgenic for S138 wild type cervid PrP, or the N138 variant associated with resistance to chronic wasting disease. We show that cervid PrP Drosophila accumulate bona fide prion infectivity after exposure to cervid prions. Furthermore, S138 and N138 PrP fly lines are susceptible to cervid prion isolates from either North America or Europe when assessed phenotypically by accelerated loss of locomotor ability or survival, or biochemically by accumulation of prion seeding activity. However, after exposure to European reindeer prions, N138 PrP Drosophila accumulated prion seeding activity with slower kinetics than the S138 fly line. These novel data show that prion susceptibility characteristics of cervid PrP variants are maintained when expressed in Drosophila, which highlights this novel invertebrate host in modelling chronic wasting disease.
... These relative differences in prevalence are similar to the sex and age patterns (Grear et al., 2006;Nobert et al., 2016) and rates of infection (Ketz et al., 2022;Samuel & Storm, 2016) previously reported in Wisconsin and elsewhere. At these equilibrium levels, disease-associated mortality is expected to result in a younger age distribution of males and females, and to lower population abundance due to disease-associated mortality in males and especially in reproductive females (Edmunds et al., 2016;Jennelle et al., 2014;Ketz et al., 2019Ketz et al., , 2022Samuel & Storm, 2016;Wasserberg et al., 2009). ...
Abstract Chronic wasting disease (CWD) is a fatal neurological disease of cervids caused by a misfolded protein with no vaccines or other cures to prevent infection and death. In the past decade, CWD has been recognized as one of the 10 most important challenges facing wildlife management. This paper evaluates the temporal and spatial patterns of CWD prevalence in southern Wisconsin white‐tailed deer during the past 20 years. In most CWD areas, prevalence progresses from introduction to enzootic equilibrium in 15–20 years. In some monitoring areas, the disease grows at a much slower rate and remains below the equilibrium levels. Outbreaks are characterized by four distinct epizootic stages. Disease establishment (Stage 1) depends on the distance from a CWD focus. High rates of incidence and prevalence growth (Stage 2) are followed by slower growth as the relative number of susceptible deer declines (Stage 3). The rate of prevalence increase over time is higher in more forested ecoregions and in males (0.48 vs. 0.43) but similar in females (0.43 vs. 0.37) and yearlings (0.44 vs. 0.39). Habitat features, acting as surrogates for deer behavior and contact, may affect the rate of prevalence growth at a landscape (ecoregion) scale. Additionally, prevalence may be affected by deer management practices that favor higher deer abundance and more mature males. Finally, enzootic equilibrium (Stage 4) is higher in males (0.5), followed by females (0.36) and then yearlings (0.26). These equilibrium prevalence levels are high enough to have significant population impacts, reduce the abundance of mature males, and facilitate CWD spread by infected yearlings. Epizootic patterns suggest that CWD transmission has been frequency‐dependent and primarily driven by direct contact with infected deer. Evidence for a meaningful change in the epizootic pattern from a 10‐year management program to reduce deer abundance is lacking. The trajectory of CWD dynamics in Wisconsin suggests rapid growth in regional prevalence following introduction and increased spread across the landscape.
