Environmental correlates and fine-scale distribution of Amblyomma americanum, Ehrlichia spp., and Rickettsia amblyommatis at a single site in south-central Virginia.

Background: As tick-borne disease cases surge in the southeastern United States, there is a growing need to understand the ecological risk factors and distribution of the most abundant tick vector, Amblyomma americanum. While previous research has examined ecological factors influencing other tick vectors, such as Ixodes scapularis, few studies have evaluated micro-landscape variables associated with A. americanum abundance. Moreover, the spatial distribution of tick vectors is rarely studied at biologically relevant, fine-scale resolutions (i.e., < 100 m).

Methods: In this study, we applied a 5-m² sampling grid to a field site with diverse habitat structure to identify the micro-landscape variables associated with adult and nymphal abundance of A. americanum using linear modeling approaches. We also characterized the spatial distribution patterns of both life stages across our field site using hotspot analyses. Lastly, we applied the same hotspot analyses to ticks infected with Ehrlichia spp. and Rickettsia amblyommatis, two microbial agents associated with A. americanum in nature.

Results: We found that different landscape variables at field site influenced adult and nymphal abundance of A. americanum, with edge habitat emerging as a significant predictor for both life stages. While adults were broadly distributed across habitat types, nymphs were more spatially restricted to forested areas, aligning with previous observations of nymphal distribution patterns.

Conclusions: The significance of edge habitat and forest variables on A. americanum abundance highlights promising targets for control interventions and can be used to develop public health recommendations to reduce tick encounter risk and subsequent pathogen transmission.