Forest associated habitat variables influence human-tick encounters in the southeastern United States

Due to the increased frequency of human-tick encounters and expanding ranges of ticks in the United States, there is a critical need to identify environmental conditions associated with tick populations and their likelihood to contact human hosts. In a passive tick surveillance partnership with the United States Department of Agriculture Forest Inventory and Analysis (FIA) program, we identified environmental variables associated with tick encounters by forestry personnel. Ticks were identified to species and life stage and site-specific variables were associated with each tick using FIA forest inventory datasets and generalized linear and zero-inflated models. Of the 55 FIA variables available, we identified biotic and abiotic environmental variables associated with Amblyomma americanum (carbon in litter material and standing dead tree aboveground dry biomass), Dermacentor variabilis (live sapling belowground dry biomass, carbon in litter material, forest stand age, and elevation), and Ixodes scapularis (carbon in dead woody material and seedling species unevenness). We propose that land management decisions not only affect common flora and fauna but changes to these habitats can also alter the way ticks parasitize hosts and use vegetation to find those hosts. Testing of these results can be used with land management decisions to prevent future encounters and highlight risk areas. Foresters that inventory sites encounter ticks, which we can then use to better understand the environmental conditions conducive to increased tick abundance or habitat suitability.

Methods
Data for this study were obtained through a partnership with the USDA-FIA. Ticks were collected voluntarily according to methods outlined in Trout Fryxell and Vogt 2019 by FIA foresters conducting standard inventory operations over a period of five years (2017–2021) in the southeastern U.S.  Vegetation data were collected by USDA-FIA crews on permanent ground sampling plots located across the study area at a sampling intensity of 1 plot per 2,428 ha. Crews indicated where ticks were encountered and those plots were cross-referenced with the USDA FIA database.