Habitat amount, quality, and fragmentation associated with prevalence of the tick-borne pathogen Ehrlichia chaffeensis and occupancy dynamics of its vector, Amblyomma americanum
Tick-borne diseases are becoming increasingly prevalent world-wide. This is likely due in part to land-cover change, particularly forest fragmentation, but this evidence is largely limited to Lyme disease. It is unknown whether this is generalizable to other, emergent tick-borne pathogens.
Motivated by hypotheses regarding landscape context and vertebrate hosts, we asked how landscape context, namely habitat amount, quality, and fragmentation, is related to the distribution of Ehrlichia chaffeensis, a tick-borne pathogen of increasing concern, and the interannual occupancy dynamics of its vector, the lone star tick (Amblyomma americanum).
We collected nymphal ticks from 130 plots in southeastern Virginia, U.S., for 5 years and tested for E. chaffeensis via targeted PCR. We derived metrics of landscape context from Landsat data and related these to pathogen prevalence and tick turnover using hierarchical Bayesian models.
Landscape context was associated with both pathogen prevalence and tick turnover. Pathogen prevalence was negatively associated with total forest landcover, coniferous forest landcover, and forest edge density. Tick turnover was positively associated with coniferous landcover and with an interaction between total forest landcover and edge. This interaction was such that turnover was predicted to be lowest in small contiguous forests, and highest in small fragmented forests.
Landscape context affects E. chaffeensis prevalence and occupancy dynamics of its tick host, though these processes appear decoupled. We hypothesize that pathogen prevalence may be more driven by reservoir host movement and social behavior and tick dynamics are more driven by host population density.
KeywordsEhrlichia chaffeensis Amblyomma americanum Tick-borne disease Forest fragmentation Edge effect
We thank Andrew Lewis, Julia Moore, Joseph Thompson, Alan Harris, Richard Cannella, Matt Feresten, Ann Marie Rydberg, Christopher Tyson, Stephanie Wilson, James Woods, and Nora Wicks for help collecting ticks. We thank Phillip D’Addio for his help with molecular analyses. We are grateful to the following landowners for providing access: Colonial National Historical Park, Colonial Williamsburg, Newport News Park, Waller Mill Park, Freedom Park, Greensprings Trail Park, York River State Park, Joint Base Langley-Eustis, and the Virginia State Department of Forestry. This work was supported by William & Mary’s Commonwealth Center for Energy and the Environment, Charles Center, and Environmental Science and Policy Program, and the Strategic Environmental Research and Development Program (RC-2202).
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