Abstract
Two tick-borne diseases with expanding case and vector distributions are ehrlichiosis (transmitted by Amblyomma americanum) and rickettiosis (transmitted by A. maculatum and Dermacentor variabilis). There is a critical need to identify the specific habitats where each of these species is likely to be encountered to classify and pinpoint risk areas. Consequently, an in-depth tick prevalence study was conducted on the dominant ticks in the southeast. Vegetation, soil, and remote sensing data were used to test the hypothesis that habitat and vegetation variables can predict tick abundances. No variables were significant predictors of A. americanum adult and nymph tick abundance, and no clustering was evident because this species was found throughout the study area. For A. maculatum adult tick abundance was predicted by NDVI and by the interaction between habitat type and plant diversity; two significant population clusters were identified in a heterogeneous area suitable for quail habitat. For D. variabilis no environmental variables were significant predictors of adult abundance; however, D. variabilis collections clustered in three significant areas best described as agriculture areas with defined edges. This study identified few landscape and vegetation variables associated with tick presence. While some variables were significantly associated with tick populations, the amount of explained variation was not useful for predicting reliably where ticks occur; consequently, additional research that includes multiple sampling seasons and locations throughout the southeast are warranted. This low amount of explained variation may also be due to the use of hosts for dispersal, and potentially to other abiotic and biotic variables. Host species play a large role in the establishment, maintenance, and dispersal of a tick species, as well as the maintenance of disease cycles, dispersal to new areas, and identification of risk areas.
Highlights
The roles of Amblyomma americanum, Amblyomma maculatum (Gulf coast tick), and Dermacentor variabilis (American dog tick) in tick-borne disease (TBD) transmission has been directed at host association studies [1,2,3,4,5,6], but field studies investigating habitat use and niche partitioning where these species co-exist are severely lacking
A total of 5050 ticks were collected in June 2014 from the 76 sites consisting of 4904 (97.11%) A. americanum, 128 (2.53%) D. variabilis, 11 (0.22%) A. maculatum, and 7 (0.14%) I. scapularis (Table 1)
Additional A. americanum larvae were encountered throughout the study by the investigators, but were not included in the analysis because the investigators could not guarantee where each was acquired due to size for detection and walking into sites
Summary
The roles of Amblyomma americanum (lone star tick), Amblyomma maculatum (Gulf coast tick), and Dermacentor variabilis (American dog tick) in tick-borne disease (TBD) transmission has been directed at host association studies [1,2,3,4,5,6], but field studies investigating habitat use and niche partitioning where these species co-exist are severely lacking. These tick species’ distributions overlap with one another [5,6,7,8]. Within the southeastern United States both Ehrlichia and Rickettsia diagnoses are increasing, likely due, in part, to increasing tick numbers and expanding ranges [19]
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