Wildlife Diseases II

Contributed Oral

Modeling Nymph and Adult Black-Legged Tick Relative Abundance at Fort Drum Military Installation in New York Using Geographically Referenced Data
Lucas Price, John Edwards, Christopher Rota, Sheldon Owen, Aaron Maxwell, Raymond Rainbolt

The black-legged tick (Ixodes scapularis) is the primary vector of Lyme disease in the eastern United States. Although several studies have modeled tick abundance across a broad geographical range, there is little research predicting tick abundance at the local scale. To accomplish our goal of making localized predictions, we surveyed tick relative abundance at 46 sites across the Cantonment Area at Fort Drum Military Installation in northern New York. We conducted tick drag surveys every two weeks over a 12-week period during the summers of 2018, 2019, and 2020. Numbers of nymph and adult black-legged ticks collected each summer were used as indexes of relative abundance. We collected geographically referenced data and extracted predictor variables of interest for each tick drag survey site. We then used Negative Binomial generalized linear models to predict nymph and adult black-legged tick relative abundance using the geographically referenced data. Tick relative abundance was positively associated with coniferous and mixed forest cover, moderate soil available water capacity, and areas far from roads. Distance to water was negatively related to nymph tick relative abundance, and soil pH was positively related to adult tick relative abundance. We then mapped expected tick relative abundance across the Fort Drum Cantonment Area using the Negative Binomial models. Predicted surface maps of tick relative abundance are useful in managing military or public use of areas of high abundance or in educating people of the potential risk when they visit an area.

CWD Show and Tell: Gauging Hunters’ Willingness to Adopt Management Practices
Sonja Christensen, Danielle Ufer, Krysten Schuler, David Ortega, Nick Pinizzotto

Chronic wasting disease (CWD) threatens wild cervid populations and the funds available to manage and conserve wildlife. Despite the increasingly widespread apparent prevalence of this disease, few options to control or manage it have been successful. Many of the disease management options available to state wildlife agencies rely on deer hunters complying with new regulations or voluntarily changing behavior following suggested best management practices for harvesting and handling potentially infected animals. Research in behavioral psychology has shown improved success with changing human behavior when subjects are provided with visual demonstrations of the desired action. We created short (< 2 min) videos for deer hunters that demonstrate a series of best management practices for reducing the spread of CWD. We assessed the impact of these videos on hunter intent to accept management actions via a survey before deer season in October 2020, and actual behavior via a follow-up survey of the same individuals in February 2021 (after the deer season). To assess each information treatment against a control, we randomly selected hunters from our total sample to participate in each survey group, including groups that received no information treatment or a placebo treatment. We received 1,450 completed surveys with full baseline, initial intent, and endpoint responses from across the U.S. We evaluated factors including landownership type, region, and CWD proximity. The effects of video treatments varied by behavior type and by stated intent versus actual behavior during the deer season, with actual hunter behavior generally less influenced by video treatments than intent. Our survey results and hunter behavior assessment provide critical insight into CWD management adoption and the opportunities for behavior change relative to disease mitigation strategies. Understanding how information campaigns result in differences in hunter behavior is vital for evaluating and targeting successful CWD management options and prioritizing resources.

Potential for Chronic Wasting Disease Transmission at Scrapes of White-Tailed Deer
Michael Egan, Kim Pepin, Justin Fischer, Scott Hygnstrom, Kurt VerCauteren, Guillaume Bastille-Rousseau

Indirect transmission of chronic wasting disease (CWD) among white-tailed deer (Odocoileus virginianus) results from shedding and uptake of infectious prions. Scrapes are focal sites for chemical communication by males during breeding, and an understudied source of prion transmission. Variation in behaviors at scrapes likely impact transmission but have not been studied. We test the effects of behavior on social networks representing deer as nodes and potential CWD transmission as edges. Cameras recorded scrape visits and behaviors at scrapes throughout DeSoto Wildlife Refuge in eastern Nebraska in fall of 2005 and 2006. Based on 5,009 scrape encounters and 1,830 direct interactions, and unique individual characteristics, we identified 303 individual male deer. We generated social networks with increasing behavioral complexity, where behavioral complexity is defined by the order and number of visits and the CWD shedding and uptake risk of scrape-related behaviors. We estimated centrality metrics characterizing the potential for disease transmission by individuals and modeled centrality as a function of the complexity of the behavioral model and individual-level covariates characterizing landcover, distance traveled, and age. We found that the level of behavioral complexity impacted heterogeneity in disease transmission potential. Deer from weighted networks (accounting for repeated visits) had greater potential for transmission to others but lower potential to facilitate transmission through the network. In networks accounting for scrape behavior, individuals facilitated transmission to a greater degree. Deer that traveled farther had greater transmission potential and older deer had greater potential to facilitate transmission. We found interaction effects between agriculture and the level of behavioral complexity of the network. Our results indicate that accounting for behavior in indirect contacts may lead to different inferences about heterogeneity in the risk of disease transmission. These differences are important because behavior may be used to target the most high-risk individuals and locations for management.

Characterization of the Prion Protein Gene in Axis Deer and Implications for Susceptibility to Chronic Wasting Disease
Matthew Buchholz, Emily Wright, Blake Grisham, Robert Bradley, Thomas Arsuffi, Warren Conway

Chronic wasting disease (CWD) affects both native and non-native North American Cervids.  The expanding geographic distribution of CWD and list of affected species is concerning, especially for stakeholders who manage Cervid populations or harvest wild animals.  In areas where native and non-native Cervids overlap, the potential for interspecific transmission of CWD is of concern when the CWD susceptibility of the non-native species is unknown.  Axis deer (Axis axis) occur both in captivity and free-ranging populations in portions of North America but to date, no data exist pertaining to their susceptibility to CWD.  Because CWD susceptibility is linked to the amino acid (AA) sequence of the prion protein (PrPC), we obtained DNA sequences of PRNP exon 3, the gene that encodes PrPC, from 133 axis deer to assess potential susceptibility to CWD. We identified and compared AA substitutions in axis deer PrPC to substitutions reported to confer reduced susceptibility in Cervids and compared the axis deer sequence to those of CWD-susceptible species.  A single PRNP allele without individual variation was recovered from axis deer, that indicates axis deer PRNP is most similar to North American elk (Cervus canadensis) PRNP in both nucleic and translated AA sequence.  The AA sequence similarity to elk suggests that axis deer are likely susceptible to CWD, but with a potentially lower susceptibility level than white-tailed deer (Odocoileus virginianus).  We recommend increased CWD surveillance for axis deer focused on areas where CWD has been detected and axis deer coexist with native North American CWD susceptible species.

Testing the Assumption of Homogeneity in Disease Theory: Patterns of Transmission and Virulence of Malaria Infecting Anole Lizards
John Toohey, Miguel Acevedo

Heterogeneous distributions are a fundamental principle of ecology, manifesting as natural variability within ecological levels of organization from individuals to ecosystems. Despite empirical evidence of the role of host and spatial heterogeneities as drivers of vector-borne disease dynamics, our classic theoretical understanding of these diseases comes from models that instead assume homogeneous transmission and virulence. Here we test this assumption by asking whether heterogeneity exists in the transmission and virulence of two lizard malaria systems: three malaria parasites (Plasmodium floridense, P. leukocytica and P. azurophilum) infecting the lizard Anolis gundlachi in the rainforest of Puerto Rico and a single parasite system (P. floridenseA. sagrei) in Florida. Using a Bayesian model selection framework, we evaluated whether individual host differences – (1) body size and (2) sex – or spatial variability – (3) local-scale spatial structure and (4) habitat type – drive heterogeneity in the probability of infection of a lizard or in virulent effects of infection (i.e. body condition, blood chemistry).  Our results suggest that the probability of infection increases with lizard length in both systems. However, in Florida where sampling was conducted pairwise across two types of habitat, we found that relationship to be subdued in non-forested habitats compared to the Floridian and Puerto Rican forests. Furthermore, infection was spatially clustered, with “hot” and “cold” spots across the landscape. Results for virulence are less consistent. No pattern was evident for body condition in Puerto Rican anoles, while body condition decreased in A. sagrei due to infection, at shorter lengths, and in non-forested sites. Meanwhile, infection showed no significant influence on blood electrolytes or hematology. Our results show that transmission and virulence are heterogeneous, but the driving sources of heterogeneity are not consistent across systems. We encourage disease ecologists to consider potential system-specific sources of heterogeneity in their models.

Modeling Mitigation Strategies for Bat Populations Experiencing Severe Mortality from White-Nose Syndrome
John Grider, Wayne Thogmartin, Riley Bernard, Robin Russell

Since its discovery in 2007, white-nose syndrome has resulted in numerous bat species experiencing population declines greater than 90%. This severe mortality has prompted efforts to develop treatments for bats affected by the disease. As treatments become available for large-scale application, resource managers will be tasked with establishing management plans that optimize the long-term survival of bat populations. To help managers strategize, we developed a model that allows for the implementation of different treatment scenarios for bat populations at risk of severe mortality from white-nose syndrome. Our model allows for variation in over 10 parameters, including: effectiveness of treatment, treatment disturbance, number of individuals treated, number of hibernacula treated, herd immunity, and movement. Additionally, the model allows treatments to be applied to individuals, the hibernaculum, or a combination of the two. We simulated treatments for hypothetical populations of 100,000, 10,000, and 1,000 individuals, with the distribution of number of individuals within hibernacula based on field surveys of Myotis lucifugus. When treatments were applied directly to individuals, we broke treatments into three categories, high, medium, and low effort, based on the maximum number of individuals that could be treated each year. The most influential predictor of treatment success for direct treatment of individuals was the number of bats effectively treated, followed by the magnitude of disturbance and year of first treatment (i.e., how long after Pd was introduced to a hibernaculum). For treatments applied directly to hibernacula, year of first treatment, magnitude of disturbance, and effectiveness of treatment were the best predictors of treatment success. Single treatments applied to individuals were often the most successful treatment option; however, all populations and treatment levels had substantial variation across outcomes, highlighting the importance of obtaining field estimates of parameters associated with treatments (including negative effects of disturbance from treatments).

Data Driven Management–A Dynamic Occupancy Approach to Enhanced Rabies Surveillance Prioritization
Amy Davis, Jordona Kirby, Richard Chipman, Kathleen Nelson, Amy Gilbert

The raccoon variant of the rabies virus (RRVV) is enzootic across the eastern United States. Intensive management of RABV, particularly using oral rabies vaccination (ORV), has prevented the spread of RRVV westward and shown evidence of local elimination in the northeastern US. The USDA, Wildlife Services, National Rabies Management Program (NRMP) collaborates with other agencies and organizations to implement broad-scale wildlife rabies management targeting meso-carnivores and conducts extensive program monitoring to measure effectiveness and efficiency.  Effective surveillance is critical to ensure that management is directed along the leading edge of the enzootic area, to ensure management is successful in reducing RRVV occurrence, and detects any incidence of RRVV west of managed areas.  During 2005, Enhanced Rabies Surveillance (ERS) was initiated in all states with RRVV management. In 2016, ERS protocols were changed to direct surveillance efforts to higher value rabies samples by assigning points to different surveillance categories (including: strange-acting, found-dead, roadkill, surveillance-trapped, nuisance reported, and other; point values ranged from 1 to 15).  Point values were assigned using preliminary ERS data and expert opinion.  We used ERS data from 2012-2015 (prior to the point-system) and 2016-2019 (during the point-system use) to examine the impact of the point-system on surveillance data.  Additionally, we used the 2016-2019 data to re-evaluate the point values by category using a dynamic occupancy model. Implementation of the point-system increased positivity rates of samples by 64%, indicating a substantial increase in the efficiency of the ERS system.  In our re-evaluation of point values, most points accurately reflect the value of the surveillance samples.  The notable exception was that samples from animals found dead were considerably more valuable than originally thought (original points =5, new points=20).  This work demonstrates how the NRMP has refined and improved enhanced rabies surveillance in support of effective wildlife rabies management.

Extension Programming Educates Hunters on Chronic Wasting Disease
Bonner Powell, Mark Turner, Neelam Poudyal, Allan Houston, Bronson Strickland, Craig Harper

Concerns and interests among hunters can change quickly upon discovery of chronic wasting disease (CWD). Hunter participation may decline if deer density and sightings are reduced significantly and if there is perceived danger of eating the meat. We surveyed hunters of the Ames Plantation Hunting Club in May 2019 to determine concerns, opinions, and attitudes about CWD, which was discovered at Ames Plantation in December 2018. We received 66 completed surveys for a response rate of 78%. Ames hunters were extremely (60%) or moderately (26%) concerned upon discovery of CWD. Of their concerns, deer sightings was the most important (71%) factor related to hunter satisfaction, and 57% of hunters believed deer sightings will be reduced because of CWD. Hunters (67%) did not favor reducing deer density additionally at Ames Plantation after discovery of CWD. Additionally, hunters (94%) expressed concern about eating meat that may contain the disease and stated they would not consume meat from an untested deer harvested in an area with CWD. Members hunted 44% fewer hours than the average of the previous five seasons during 2019 deer season, the first season after the discovery of CWD, and doe harvest in 2019 was 78% lower than the previous five seasons. However, deer observations per hour were similar to previous seasons, and buck harvest was only 11% below the previous five-season average. The decline in doe harvest is concerning, as hunters are the only viable population management tool currently available at Ames Planation. Extension programming can play a key role in educating hunters and helping reduce the spread of CWD, but educational programs should be tailored to provide information in several key areas. Our survey results provide state wildlife agencies and extension professionals with useful information to better understand and address hunter concerns regarding CWD.

Contributed Oral
Location: Virtual Date: November 5, 2021 Time: 4:00 pm - 5:00 pm