Chronic Wasting Disease

Contributed Paper
ROOM: CC, Room 21
SESSION NUMBER: 93
 

1:10PM Forecasting the Impacts of Chronic Wasting Disease
Nathan L. Galloway; Ryan J. Monello; Doug Brimeyer; Eric Cole; N. Thompson Hobbs
Chronic wasting disease (CWD) is a prion disease of the deer family. CWD has infected mule deer (Odocoileus hemionus) in close proximity to the National Elk Refuge in the Jackson Hole area of Wyoming. Prior observations suggest CWD may have a greater impact in high-density populations resembling conditions on the Refuge. We developed a Bayesian model for the Jackson elk herd to (1) examine the potential impacts of CWD on population dynamics, (2) aid in future sampling for CWD, and (3) provide a framework for new herd health data to guide adaptive management. We fit the model using total census, demographic classifications, and CWD test results from the Jackson elk herd and findings from a CWD-infected elk population in Rocky Mountain National Park (RMNP). The model enables predictions of the future state of the population accompanied by rigorous estimates of uncertainty. Analysis revealed that CWD will likely drive the population growth rate (λ) below one, indicating a decline in elk numbers over time. A declining population becomes more probable with increasing disease prevalence. The most probable threshold between an increasing and a declining population λ=1 occurred at 7% CWD prevalence in yearling and adult females assuming no hunting. However, we cannot rule out a threshold as high as 23% prevalence before λ falls below one. These results may be conservative because they depend in part on research results from elk populations infected with CWD in RMNP, a smaller and presumably less concentrated population. Thus, it is prudent to assume that CWD may lead to higher disease prevalence and greater impacts on the Jackson elk herd due to crowded herds returning annually to the same location as are often associated with such feedgrounds.
1:30PM Influence of the Geographic Distribution of Prion Protein Gene Sequence Variation on Patterns of Chronic Wasting Disease Spread in White-Tailed Deer
Adam L. Brandt; Michelle L. Green; Yasuko Ishida; Alfred L. Roca; Jan Novakofski; Nohra E. Mateus-Pinilla
Managing and controlling the spread of diseases in wild animal populations is challenging, especially for highly social and mobile species. Effective management would benefit from information about disease susceptibility, allowing limited resources to be focused on areas or populations with a higher risk of infection. Chronic wasting disease (CWD), a transmissible spongiform encephalopathy that affects cervids, was first detected in Colorado. In 2002 CWD was detected in Illinois and Wisconsin and has since spread through many counties. Specific nucleotide variations in the prion protein gene (PRNP) sequence have been associated with reduced susceptibility to CWD in white-tailed deer. Though genetic resistance is incomplete, the frequency of deer possessing these mutations in a population is an important factor in disease spread (i.e. herd immunity). In this study we sequenced 625 bp of the PRNP gene from a sampling of 2433 deer from Illinois and Wisconsin. In north-central Illinois where CWD was first detected, counties had a low frequency of protective haplotypes (frequency < 0.20); whereas in northwestern Illinois counties, where CWD cases have only more recently been detected, the frequency of protective haplotypes (frequency > 0.30) was much higher (p < 0.05). Protective haplotype frequencies varied significantly among infected and uninfected geographic areas. The frequency of protective PRNP haplotypes may contribute to population level susceptibility and may shape the way CWD has spread through Illinois. Analysis of PRNP haplotype distribution could be a powerful tool to assess CWD risk and best allocate resources to contain and reduce the spread of infection.
1:50PM Models to Predict Spread of Chronic Wasting Disease in Alberta
Eleanor Stern; Anne Hubbs; Brad Stelfox; Margo Pybus; Mark Ball; Evelyn Merrill
Chronic Wasting Disease (CWD) is an emerging threat to cervid populations in North America, and now other portions of the world. A growing body of research is working to explain the transmission of CWD, but a better understanding of animal and environmental factors influencing the disease spread is needed to support management programs. We use ALCES Online (www.alces.ca), a spatially explicit landscape and population simulation model to predict the rate of spread of CWD through eastern Alberta based on predicted landscape and anthropogenic changes. The model is parameterized for sympatric sub-populations of positive and negative mule deer (Odocoileus hemionus) in eastern Alberta based on movement, habitat selection, reproductive and survival data from local telemetry studies, population size and composition from aerial surveys, age structure from teeth, and hunter harvest data. The model was calibrated retrospectively predicting the observed spread of CWD over a 12-year period since its first detection in 2 areas of Alberta in 2005 using continuous, harvest-based surveillance data. We present a sensitivity analysis to major model components (e.g., deer densities, landscape patterns, harvest rates, and assumptions in animal-to-animal and environmental disease transmission) and project the future spread of CWD in mule deer over the next 15 years under multiple harvest scenarios with and without anticipated landscape change. The effort supports a Canadian and international initiative to better understand how this disease moves, and will provide information that is integral to forming a proactive and effective strategy to managing CWD in Alberta.
2:10PM Lessons Learned From Chronic Wasting Disease Sampling in Ohio
Scott Peters; Michael Tonkovich
In October of 2014, Ohio confirmed the first case of Chronic Wasting Disease (CWD) in a captive white-tailed deer (Odocoileus virginianus) herd. A 10-township disease surveillance area (DSA) was established, which prohibited baiting and mandated hunters to submit their deer for CWD testing during firearms deer seasons. Deer hunters had only a two week notice in year one and testing compliance was approximately 60% the first year of mandatory CWD sampling. Compliance rates (~40-45%) sharply declined in years two and three. An extensive information & education campaign was employed to advise hunters on compliance with our DSA laws prior to year three of mandatory CWD sampling to avoid law enforcement action. A variety of techniques to obtain CWD samples were used during archery season (non-mandatory hunter harvest sampling timeframe) such as paying deer processors, calling hunters after they reported a harvest, and providing drop-off locations to help obtain our desired sample size. Over 2,100 deer have been tested for CWD in the DSA without any positive deer detected. We examined costs versus the benefits of the different collection techniques and provide recommendations to efficiently obtain CWD samples.
12:50PM Are There Canonical Decision Problems in Managing Emerging Infectious Diseases of Wildlife?
Riley F. Bernard; Evan H. C. Grant
Emerging infectious diseases (EIDs) of wildlife are notoriously difficult to manage, leading to reactive and often ineffective management strategies. Currently, two fungal pathogens, Pseudogymnoascus destructans (Pd) and Batrachochytrium salamandrivorans (Bsal), are causing declines in novel host species, leaving managers with little time, and few options, to respond. As risk of fungal pathogens increases, necessitating the need for an improved response model, we aimed to identify the underlying challenges that often lead to delayed rather than proactive disease management actions. Using an online survey platform, we queried wildlife managers, motivated by Pd and Bsal, regarding their management concerns, objectives, and disease mitigation actions. We also characterized their impediments to initiating disease mitigation actions to identify if there are characteristics of EID management that are shared across agencies and pathogens. We received 91 Pd and 81 Bsal responses from state, federal and provincial agencies. Across both pathogens, 52% of managers felt the most pressing concern was the current or possible loss of susceptible species. However, this concern did not necessarily lead to proactive management, with most managers stating the need to consider multiple management objectives such as multi-use management, public use, and other species of conservation concern. Although managers would consider initiating proactive responses to EIDs, the amount of uncertainty and associated risk with untested treatments often outweighs the fear of species loss. By formally framing management problems as decisions, managers can effectively identify possible proactive solutions and recognize context-specific constraints, such as agency mandates, trade-offs among other mission elements, and relevant uncertainties that aid in recognizing and sustaining conservation success through proactive management actions. Although Pd and Bsal affect different taxa, we identified aspects of each decision problem that were shared regardless of pathogen, region, or agency, suggesting that there are indeed canonical decision problem elements for fungal pathogen management.

 

Contributed Paper
Location: Cleveland CC Date: October 11, 2018 Time: 12:50 pm - 2:30 pm