Identification and Characterization of Peak Activity, Environmental Variables, and Bacterial Pathogens in A. americanum L. at Ames Plantation, West Tennessee

The status of tick-borne diseases (TBD) in the southeastern United States is uncertain due to a number of factors including, but not limited to emerging pathogens, misdiagnoses, and modifications to landscapes. Ehrlichiosis and rickettiosis are two of the most common TBDs; these are caused by Ehrlichia and Rickettsia bacteria that can be transmitted by a number of different tick species. The objectives of this study were to identify Amblyomma americanum (the Lone Star tick) peak activity and habitat preferences and characterize the potential role of A. americanum in tick-borne disease cycles in southwestern Tennessee. Using vegetation drags and CO₂-baited traps, ticks were collected monthly from May to September 2012 from 100 sites on the Ames Plantation Research and Education Center (Ames). Using a one-way analysis of variance, we identified the peak activity of A. americanum for adults as being in May or June and of nymphs as being bimodal with a peak in June and again in August. Trapping data were analyzed in a contingency table; results indicated significant trapping differences in the number of nymphs and adults collected by the two trapping methods. Environmental and trapping data were correlated using an ANCOVA to evaluate trapping efficacy under different environmental stressors and to identify landscapes in which A. americanum adults and nymphs are notably more abundant. Of 925 adult A. americanum screened for Ehrlichia and Rickettsia bacteria, 1.8% (n = 17) and 38% (n = 353) were PCR positive, of which 8 ticks (0.8%) were positive with both pathogens. Using ArcGIS we displayed pathogen positive A. americanum locations; calculating Moran’s I for each pathogen indicated there was no significant clustering among pathogen positive locations. The identification of pathogens and co-infections within A. americanum from western Tennessee warrants further investigations to understand the role ticks and their environment have in the distribution of TBD.