Host culling as an adaptive management tool for chronic wasting disease in white‐tailed deer: a modelling study

Abstract

Summary 1.Emerging wildlife diseases pose a significant threat to natural and human systems. Because of real or perceived risks of delayed actions, disease management strategies such as culling are often implemented before thorough scientific knowledge of disease dynamics is available. Adaptive management is a valuable approach in addressing the uncertainty and complexity associated with wildlife disease problems and can be facilitated by using a formal model. 2.We developed a multi-state computer simulation model using age, sex, infection-stage, and seasonality as a tool for scientific learning and managing chronic wasting disease (CWD) in white-tailed deer Odocoileus virginianus . Our matrix model used disease transmission parameters based on data collected through disease management activities. We used this model to evaluate management issues on density-(DD) and frequency-dependent (FD) transmission, time since disease introduction, and deer culling on the demographics, epizootiology, and management of CWD. 3. Both DD and FD models fit the Wisconsin data for a harvested white-tailed deer population, but FD was slightly better. Time since disease introduction was estimated as 36 (95% CI, 24-50) and 188 (41->200) years for DD and FD transmission, respectively. Deer harvest using intermediate to high non-selective rates can be used to reduce uncertainty between DD and FD transmission and improve our prediction of long-term epidemic patterns and host population impacts. A higher harvest rate allows earlier detection of these differences, but substantially reduces deer abundance. 4. Results showed that CWD has spread slowly within Wisconsin deer populations, and therefore, epidemics and disease management are expected to last for decades. Non-hunted deer populations can develop and sustain a high level of infection, generating a substantial risk of disease spread. In contrast, CWD prevalence remains lower in hunted deer populations, but at a higher prevalence the disease competes with recreational hunting to reduce deer abundance. 5. Synthesis and applications. Uncertainty about density-or frequency-dependent transmission hinders predictions about the long-term impacts of chronic wasting disease on cervid populations and the development of appropriate management strategies. An adaptive management strategy using computer modelling coupled with experimental management and monitoring can be used to test model predictions, identify the likely mode of disease transmission, and evaluate the risks of alternative management responses.

Effects of Chronic Wasting Disease on Reproduction and Fawn Harvest Vulnerability in Wisconsin White-Tailed Deer

“…There are no specific data published, however, about how CWD progresses over time in the different Prnp genotypes in white-tailed deer except for time to clinical disease and death (Wilson et al, 2009;Johnson et al, 2011). In this study, therefore, we used average rates of disease progression that are believed to be common in our study area (Wasserberg et al, 2009). …”

“…However, the disease threshold required to reduce cervid populations likely varies based on species demography, CWD prevalence, and other sources of mortality Schuler, 2006;Edmunds, 2008;Wasserberg et al, 2009). Another important, but poorly explored, mechanism by which CWD could affect cervid populations is by reducing reproduction and recruitment (Dulberger et al, 2010).…”

Influence of the geographic distribution of prion protein gene sequence variation on patterns of chronic wasting disease spread in white-tailed deer (Odocoileus virginianus)

“…Once shed, prions have been shown to persist in the environment, potentially remaining infectious and furthering disease spread long after affected deer have dispersed [10–12]. If left unchecked CWD prevalence will increase slowly over time [13–16] and deer population densities will decline [17,18], possibly to the point of extirpation [19,20]. Negative economic impacts are also expected due to decreased hunter confidence, decline in wildlife viewing, and increased regulation of the captive cervid industry [21,22].…”

“…The program has been successful in that disease prevalence has remained relatively constant since first detection [33]; however, the area with detected infected deer has steadily grown from three counties in the first year to 17 counties by fiscal year (FY; July 1 – June 30) 2017 [32]. The role of culling in CWD management remains controversial and the efficacy may differ substantially if disease transmission is density or frequency dependent [17]. Transmission dynamics are complex and studies assessing management techniques should incorporate additional parameters such as heterogeneity in disease susceptibility.…”

Disease and the dynamics of extinction

“…A test that enabled the identification and removal of infected animals before they become infectious would increase the likelihood that a test and cull strategy would be successful. 'Test and cull' has also not proved to be successful in controlling brucellosis in bison populations in the USA [101], and modelling suggests that culling sufficient to eliminate chronic wasting disease in deer would probably cause extinction of the deer populations [102].…”