Human alteration of natural landscapes can create hotspots for emerging zoonotic diseases through a complex pathway of ecological interactions between hosts, vectors, and their environment. Here, we examine the impacts of human-mediated landscape change in the Saint Louis, Missouri region, on the emergence of several bacterial pathogens (e.g., Ehrlichia spp., Borrelia lonestari) transmitted by the lone star tick (Amblyomma americanum). Utilizing a natural gradient in human disturbance in the Saint Louis metropolitan region, we implemented a combination of field- and laboratory-based approaches to assess the effects of landscape change in this region on the abundance of ticks and their vertebrate hosts, tick infection rates with pathogens, and the distribution of tick bloodmeals among vertebrate host species.
Results/Conclusions
We found a positive relationship between the abundance of lone star ticks and white-tailed deer (Odocoileus virginianus), the preeminent host for all three life stages of this tick species. We also found a unimodal relationship between the density of white-tailed deer and the percent forest cover associated with our study sites, consistent with numerous studies which indicate that deer thrive in heterogeneous landscapes. Further, the density of lone star ticks was similarly related to percent forest cover, indicating a potential indirect mechanism by which landscape change may alter the abundance of ticks in this region via the response of a key vertebrate host. Finally, for a subset of these sites, we determined the prevalence of lone star tick-associated pathogens and thereby calculated the density of infected ticks. Again, we found a hump-shaped relationship between the density of infected ticks and percent forest cover, suggesting that intermediate levels of forest cover are correlated with high human risk of exposure to tick-borne diseases in the Saint Louis, MO region. Our results indicate that the potential impact of tick-borne diseases on human health should be incorporated in landscape planning decisions in this emerging hotspot for vector-borne pathogens.
