Julie A. Blanchong

SPATIAL EPIDEMIOLOGY OF CHRONIC WASTING DISEASE IN WISCONSIN WHITE-TAILED DEER

Chronic wasting disease (CWD) is a fatal, emerging disease of cervids associated with transmissible protease-resistant prion proteins. The potential for CWD to cause dramatic declines in deer and elk populations and perceived human health risks associated with consuming CWD-contaminated venison have led wildlife agencies to embark on extensive CWD control programs, typically involving culling to reduce deer populations. We characterized the spatial distribution of CWD in white-tailed deer (Odocoileus virginianus) in Wisconsin to facilitate CWD management. We found that CWD prevalence declined with distance from a central location, was locally correlated at a scale of 3.6 km, and was correlated with deer habitat abundance. The latter result is consistent with patterns expected for a positive relationship between density and prevalence of CWD. We recommend management activities focused on culling in geographic areas with high prevalence to have the greatest probability of removing infected individuals. Further research is needed to elucidate the factors involved in CWD spread and infection rates, especially the role of density-dependent transmission.

Landscape genetics and the spatial distribution of chronic wasting disease

Predicting the spread of wildlife disease is critical for identifying populations at risk, targeting surveillance and designing proactive management programmes. We used a landscape genetics approach to identify landscape features that influenced gene flow and the distribution of chronic wasting disease (CWD) in Wisconsin white-tailed deer. CWD prevalence was negatively correlated with genetic differentiation of study area deer from deer in the area of disease origin (core-area). Genetic differentiation was greatest, and CWD prevalence lowest, in areas separated from the core-area by the Wisconsin River, indicating that this river reduced deer gene flow and probably disease spread. Features of the landscape that influence host dispersal and spatial patterns of disease can be identified based on host spatial genetic structure. Landscape genetics may be used to predict high-risk populations based on their genetic connection to infected populations and to target disease surveillance, control and preventative activities.

Infectious Disease in Cervids of North America

Over the past two decades there has been a steady increase in the study and management of wildlife diseases. This trend has been driven by the perception of an increase in emerging zoonotic diseases and the recognition that wildlife can be a critical factor for controlling infectious diseases in domestic animals. Cervids are of recent concern because, as a group, they present a number of unique challenges. Their close ecological and phylogenetic relationship to livestock species places them at risk for receiving infections from, and reinfecting livestock. In addition, cervids are an important resource; revenue from hunting and viewing contribute substantially to agency budgets and local economies. A comprehensive coverage of infectious diseases in cervids is well beyond the scope of this chapter. In North America alone there are a number of infectious diseases that can potentially impact cervid populations, but for most of these, management is not feasible or the diseases are only a potential or future concern. We focus this chapter on three diseases that are of major management concern and the center of most disease research for cervids in North America: bovine tuberculosis, chronic wasting disease, and brucellosis. We discuss the available data and recent advances in modeling and management of these diseases.

Temporal patterns of activity of the unstriped nile rat, Arvicanthis niloticus

Abstract Previous descriptions of the daily pattern of activity of the unstriped Nile grass rat (Arvicanthis niloticus) conflict. Researchers have described this species as diurnal, nocturnal, or crepuscular. In our laboratory colony, some animals are diurnal and others are nocturnal in running wheels. We systematically examined activity patterns of free-living grass rats in the Masai Mara National Reserve, Kenya, where the animals in our lab originated. Sherman traps were set at dawn or dusk near animal burrow entrances, and the time of capture was recorded for each animal. Seventy-seven A. niloticus were captured 287 times at 20 different sites. Captures occurred almost exclusively during daylight. In contrast, other small mammals that were trapped on 49 occasions were caught exclusively at night. The temporal pattern of capture of A. niloticus did not vary as a function of age or sex. The diurnal pattern of activity we observed in A. niloticus is unusual among small rodents.

GEOGRAPHICAL GENETICS: CONCEPTUAL FOUNDATIONS AND EMPIRICAL APPLICATIONS OF SPATIAL GENETIC DATA IN WILDLIFE MANAGEMENT

Abstract Molecular-genetic technology and statistical methods based on principles of population genetics provide valuable information to wildlife managers. Genetic data analyzed in a hierarchical, spatial context among individuals and among populations at micro- and macro-geographic scales has been widely used to provide information on the degree of population structure and to estimate rates of dispersal. Our goals were to (1) provide an overview of spatial statistics commonly used in empirical population genetics, and (2) introduce analytical designs that can be employed to extend hypothesis-testing capabilities by incorporating space-time interactions and by using information on habitat quality, distribution, and degree of connectivity. We show that genetics data can be used to quantify the degree of habitat permeability to dispersal and to qualify the negative consequences of habitat loss. We highlight empirical examples that use information on spatial genetic structure in areas of harvest derivation for admixed migratory species, wildlife disease, and habitat equivalency analysis.

TB-infected deer are more closely related than non-infected deer

Identifying mechanisms of pathogen transmission is critical to controlling disease. Social organization should influence contacts among individuals and thus the distribution and spread of disease within a population. Molecular genetic markers can be used to elucidate mechanisms of disease transmission in wildlife populations without undertaking detailed observational studies to determine probable contact rates. Estimates of genealogical relationships within a bovine tuberculosis-infected white-tailed deer (Odocoileus virginianus) population indicated that infected deer were significantly more closely related than non-infected deer suggesting that contact within family groups was a significant mechanism of disease transmission. Results demonstrate that epidemiological models should incorporate aspects of host ecology likely to affect the probability of disease transmission.

Occurrence and molecular analysis of Campylobacter in wildlife on livestock farms

Wildlife harbor a variety of Campylobacter spp. and may play a significant role in the transmission of Campylobacter to livestock. Although studies have been conducted on wildlife-associated Campylobacter isolates from farms in other countries, there are little data available for livestock farms in the United States. In addition, the critical questions of whether wildlife harbor Campylobacter that is pathogenic to ruminants and/or antibiotic-resistant Campylobacter have yet to be addressed. We captured wild small mammals (n=142) and small birds (n=188) at livestock farms in central Iowa and sampled them for thermophilic Campylobacter during autumn 2009, spring 2010, and autumn 2010. Overall prevalence was 4.79%, with isolates found only in wild birds. Molecular typing revealed four multilocus sequence types (STs), three of which are novel. The remaining ST (ST-806) was found in two house sparrows and is an ST previously associated with ruminant abortion cases. Further analysis of ST-806 wild bird and ruminant abortion isolates by pulsed-field gel electrophoresis, resistance gene location, and antibiotic susceptibility tests indicated that the isolates are nearly identical. This is the first account of isolation of Campylobacter types from wild birds that are known to be pathogenic to ruminants. Furthermore, these same two wild bird isolates are resistant to the antibiotic fluoroquinolone. Our results indicate there is an overall low prevalence of Campylobacter in selected wildlife in Iowa, but suggest that wildlife may play a role in the epidemiology of pathogenic Campylobacter for domestic livestock, and may also serve as a reservoir for antibiotic-resistant Campylobacter.

Changes in Artificial Feeding Regulations Impact White-Tailed Deer Fine-Scale Spatial Genetic Structure

Abstract Human activities can change the spatial distribution of individuals within wildlife populations that in turn alters population allele frequencies and spatial genetic structure at fine scales. Artificial feeding is one such activity whose impact on wildlife physical condition, population dynamics, and transmission of disease has been well documented. To evaluate the impact of artificial feeding on the spatial distribution and social organization of white-tailed deer (Odocoileus virginianus) we estimated allele frequencies at 3 microsatellite loci for 2,177 hunter-harvested deer and characterized microgeographic genetic structure in 2 regions of the northeast lower peninsula of Michigan, USA, during and following cessation of artificial feeding. While artificial feeding was ongoing we observed no evidence of spatial genetic structure across either region. Spatial homogeneity of allele frequencies over such a large area was surprising given numerous studies that have documented spatial genetic structure in other deer populations, and it was likely a function of the aggregation of multiple kin-structured social groups (i.e., matrilines) at artificial feeding sites. Subsequently, when artificial feeding was banned, we found significant genetic differentiation among groups of deer in both regions. Detection of microgeographic genetic structure consistent with a pattern of isolation-by-distance following the ban on artificial feeding was likely the result of increased spatial segregation of social groups of related deer. Our results illustrate how analyses of the degree to which natural populations are spatially genetically structured can be used to infer the effects of human actions on wildlife movement patterns, breeding behaviors, and disease transmission that are difficult to determine using traditional methods.

Persistence of Pasteurella multocida in Wetlands Following Avian Cholera Outbreaks

Avian cholera, caused by Pasteurella multocida, affects waterbirds across North America and occurs worldwide among various avian species. Once an epizootic begins, contamination of the wetland environment likely facilitates the transmission of P. multocida to susceptible birds. To evaluate the ability of P. multocida serotype-1, the most common serotype associated with avian cholera in waterfowl in western and central North America, to persist in wetlands and to identify environmental factors associated with its persistence, we collected water and sediment samples from 23 wetlands during winters and springs of 1996–99. These samples were collected during avian cholera outbreaks and for up to 13 wk following initial sampling. We recovered P. multocida from six wetlands that were sampled following the initial outbreaks, but no P. multocida was isolated later than 7 wk after the initial outbreak sampling. We found no significant relationship between the probability of recovery of P. multocida during resampling and the abundance of the bacterium recovered during initial sampling, the substrate from which isolates were collected, isolate virulence, or water quality conditions previously suggested to be related to the abundance or survival of P. multocida. Our results indicate that wetlands are unlikely to serve as a long-term reservoir for P. multocida because the bacterium does not persist in wetlands for long time periods following avian cholera outbreaks.

White‐Tailed Deer Harvest From the Chronic Wasting Disease Eradication Zone in South‐Central Wisconsin

Abstract Chronic wasting disease (CWD) was discovered in free-ranging white-tailed deer (Odocoileus virginianus) in south-central Wisconsin in 2002. The current control method for CWD in the state is the harvest of deer from affected areas to reduce population density and lower CWD transmission. We used spatial regression methods to identify factors associated with deer harvest across south-central Wisconsin. Harvest of deer by hunters was positively related to deer density (slope = 0.003, 95% CI = 0.0001–0.006), the number of landowners that requested harvest permits (slope = 0.071, 95% CI = 0.037–0.105), and proximity to the area of highest CWD infection (slope = −0.041, 95% CI = −0.056–−0.027). Concomitantly, harvest was not impacted in areas where landowners signed a petition protesting intensive deer reduction (slope = −0.00006, 95% CI = −0.0005–0.0003). Our results suggest that the success of programs designed to reduce deer populations for disease control or to reduce overabundance in Wisconsin are dependent on landowner and hunter participation. We recommend that programs or actions implemented to eradicate or mitigate the spread of CWD should monitor and assess deer population reduction and evaluate factors affecting program success to improve methods to meet management goals.