Host functional connectivity and the spread potential of Lyme disease
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In the ecology of Lyme disease emergence, it remains unclear to what extent spread of the tick vector (Ixodes scapularis) and the pathogen (Borrelia burgdorferi) are dependent upon the dispersal of vertebrate hosts in spatially heterogeneous landscapes. Yet, empirical measure of these complex ecologically driven spread processes present conceptual and methodological challenges despite important public health implications.
To examine the relationship between landscape characteristics and tick-borne disease spread, we modeled the influence of landscape connectivity for a simplified vertebrate host community (white-footed mouse—Peromyscus leucopus, American robin—Turdus migratorius, white-tailed deer—Odocoileus virginianus) on the potential spread of the tick population compared to the pathogen in a spatially-structured landscape.
We parameterized a hybrid demographic-dispersal connectivity model by combining a series of reported host dispersal and tick burden estimates with empirically-measured tick abundance and pathogen prevalence sampled from a Lyme-endemic island landscape in Thousand Islands National Park (Ontario, Canada) and simulated several tick- and pathogen-spread scenarios.
The extent of tick spread by mice [amount of reachable habitat (ARH) = 18.0%] is considerably similar to that of robins (ARH = 18.7%), while deer support the greatest tick spread extent (ARH = 82.0%). Infected mice carrying ticks support the highest pathogen spread (ARH = 19.8%). Short-distance pathogen spread and long-distance tick spread were facilitated by intermediate stepping stone habitat fragments.
We provide evidence that host functional connectivity mediates tick spread differently than pathogen spread, and depends strongly on landscape configuration. Our study therefore emphasizes the importance of landscape spatial heterogeneity on the ecological processes that influence regional tick-borne disease spread.
KeywordsNetwork theory Tick-borne disease Stepping stones Disease ecology Host–parasite interactions Landscape configuration
Field and laboratory work was conducted as part of another project (Werden et al. 2014) and was supported by Emily Gonzales at Thousand Islands National Park (TINP); Jeff Bowman at the Ontario Ministry of Natural Resources and Forestry (OMNRF); Ian K. Barker at the Canadian Wildlife Health Cooperative (CWHC) and Robbin Lindsay at the Public Health Agency of Canada. We thank the numerous students and staff from the OMNRF, CWHC, PHAC, and TINP who contributed to field data collection and lab work. We thank the associate editor and reviewers for their constructive comments.
M-JF was supported by NSERC Discovery Grant #5134. SS was supported by grant AGL2012-31099 from the Spanish Ministry of Economy and Competitiveness. AGW was partially supported by the University of Toronto, Department of Ecology & Evolution, and by Ontario Graduate Scholarships.
Compliance with ethical standards
Conflict of interest
The authors declare that there are no conflicts of interest.
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