Anthropogenic habitat change and moderating climatic conditions have enabled the northward geographic expansion of white-tailed deer, Odocoileus virginianus, and of the parasitic nematode (meningeal worm) it carries, Parelaphostrongylus tenuis. This expansion can have consequences in dead-end host species for other ungulates because meningeal worm reduces health, causes morbidity or direct mortality, and has been attributed to population declines. In northeastern Minnesota, which marks the southern extent of the bioclimatic range for moose (Alces alces), the moose population has declined more than 50% in the last decade, with studies detecting P. tenuis in 25-45% of necropsied animals. We assessed the factors that most commonly are associated with meningeal worm infection by linking moose movement ecology with known P. tenuis infection status from necropsy. We outfitted moose with GPS collars to assess their space use and cause-specific mortality. Upon death of the subject animal, we performed a necropsy to determine the cause of death and document meningeal worm infection. We then created statistical models to assess the relationship between meningeal worm infection and exposure to hypothesized factors of infection risk based on the space use of each moose by season. Predictors included land cover types, deer space use and density, environmental conditions, and demographics of individual moose (age and sex). Moose with autumn home ranges that included more upland shrub/conifer, and individuals with high proportions of wet environments, regardless of season, had increased infection risk. In contrast, the strongest relationships we found showed that high proportions of mixed and conifer forest within spring home ranges resulted in reduced risk of infection. The spring models showed the strongest relationships between exposure and infection, potentially due to moose foraging on ground vegetation during spring. By incorporating movement of moose into disease ecology, we were able to take a top-down approach to test hypothesized components of infection risk with actual spatial and temporal exposure of individual necropsied moose. The probability of infection for moose was not influenced by deer density, although deer densities did not vary greatly within the study area (2-4 deer/km2), highlighting the importance of also considering both moose space use and environmental conditions in understanding infection risk. We suggest management strategies that use a combination of deer and land management prescriptions designed to limit contact rates in susceptible populations.
Bibliographical noteFunding Information:
We acknowledge Dr. T. R. Harris’ contributions to the study design, Drs. A. Wuenschmann and A. Armién (University of Minnesota Veterinary Diagnostic Lab) for their diagnostic work to determine the presence or absence of P. tenuis infection. Several members of our primary moose mortality response team made the project possible: E. Hildebrand, D. Plattner, D. Pauly, and M. Dexter (all of the Minnesota Department of Natural Resources). Funding was provided by the Minnesota Zoo Foundation, the Minnesota Zoo’s appropriation from the Arts and Cultural Heritage Fund created by the Clean Water, Land and Legacy Amendment, the Minnesota Department of Natural Resources, and the Minnesota Environment and Natural Resources Trust Fund (ENRTF) as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR). We appreciate the input of two anonymous reviewers and the associate editor to enhance this manuscript.
© 2020 American Society of Mammalogists, www.mammalogy.org.
- animal movement
- brain worm
- climate change
- disease ecology
- disease risk
- environmentally transmitted pathogen
- white-tailed deer