Abstract
Continuing geographic spread of chronic wasting disease (CWD) poses a serious threat to the sustainable future of cervids and hunting in North America. Moreover, CWD has been detected in captive cervids in South Korea and, in recent years, in free-ranging reindeer in Europe (Norway). Management of this disease is limited by logistical, financial, and sociopolitical considerations, and current strategies primarily focus on reducing host densities through hunter harvest and targeted culling. The success of such strategies in mitigating the spread and prevalence of CWD only upon detection is questionable. Here, we propose a proactive approach that emphasizes pre-emptive management through purposeful integration of virtual experiments (simulating alternate interventions as model scenarios) with the aim of evaluating their effectiveness. Here, we have used a published agent-based model that links white-tailed deer demography and behavior with CWD transmission dynamics to first derive a CWD outbreak trajectory and then use the trajectory to highlight issues associated with different phases of the CWD outbreak (pre-establishment/transition/endemic). Specifically, we highlight the practical constraints on surveillance in the pre-establishment phase and recommend that agencies use a realistic detection threshold for their CWD surveillance programs. We further demonstrate that many disease introductions are “dead ends” not leading to a full epidemic due to high stochasticity and harvesting in the pre-establishment phase of CWD. Model evaluated pre-emptive (pre-detection) harvest strategies could increase the resilience of the deer population to CWD spread and establishment. We conclude it is important to adaptively position CWD management ahead of, rather than behind, the CWD front.
Highlights
Chronic wasting disease (CWD) is an emerging prion disease of North American cervid populations that has been detected in free-ranging and captive cervids in 26 U.S states and three Canadian provinces as well as in free-ranging reindeer Rangifer tarandus in Norway and in captive cervids in South Korea
Based on the model-derived insights about chronic wasting disease (CWD) spread dynamics and sampling requirements, we define three phases of CWD outbreak: (a) pre-establishment phase is the early stage of the outbreak characterized by low CWD prevalence and sample size requirements that are either difficult to achieve and unsustainable or unreliable; (b) transition phase follows the pre-establishment phase, characterized by an increasing prevalence and a considerable decrease in the sample size requirement even with realistic assumptions; and (c) endemic phase characterized by rapidly increasing CWD prevalence and a corresponding decrease in sample size requirement for CWD detection using realistic assumptions
The management of CWD shares challenges common for many wildlife diseases
Summary
Chronic wasting disease (CWD) is an emerging prion disease of North American cervid populations (including white-tailed deer Odocoileus virginianus, mule deer Odocoileus hemionus, and elk Cervus canadensis) that has been detected in free-ranging and captive cervids in 26 U.S states and three Canadian provinces as well as in free-ranging reindeer Rangifer tarandus in Norway and in captive cervids in South Korea. In the early phase of the outbreak (∼10–15 years after introduction into a natural population), detection of CWD using hunter-harvested deer (non-probabilistic sampling) is difficult, if not practically impossible, because the overall prevalence remains very low and cases are clustered, not randomly distributed [18,19,20]. A modeling tool that incorporates spatial clustering of cases (like OvCWD) will be useful for determining realistic sample size requirements for confidently detecting CWD in the preestablishment phase Better still, such a tool can be used to set a realistic detection threshold to economize surveillance efforts for efficient management of CWD. Implementing such harvest strategies before CWD is detected in a region (pre-emptive strategies), with the objective of increasing the resilience of the deer population to the spread and persistence of CWD, could be an important step forward in the current fight against CWD
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