Detection of Rickettsia Species, and Coxiella-Like and Francisella-Like Endosymbionts in Amblyomma americanum and Amblyomma maculatum from a Shared Field Site in Georgia, United States of America.

Abstract

Two abundant species of aggressive ticks commonly feed on humans in Georgia: the Gulf Coast tick (Amblyomma maculatum) and the Lone Star tick (A. americanum). A. maculatum is the primary host of Rickettsia parkeri, "Candidatus Rickettsia andeanae," and a Francisella-like endosymbiont (AmacFLE), whereas A. americanum is the primary host for R. amblyommatis, Ehrlichia chaffeensis, E. ewingii, and a Coxiella-like endosymbiont (AamCLE). Horizontal transmission of R. parkeri from A. maculatum to A. americanum by co-feeding has been described, and R. amblyommatis has been found infrequently in A. maculatum ticks. We assessed the prevalence of these agents and whether exchange of tick-associated bacteria is common between A. maculatum and A. americanum collected from the same field site. Unengorged ticks were collected May-August 2014 in west-central Georgia from a 4.14 acre site by flagging and from humans and canines traversing that site. All DNA samples were screened with quantitative PCR assays for the bacteria found in both ticks, and the species of any Rickettsia detected was identified by species-specific TaqMan assays or sequencing of the rickettsial ompA gene. Only R. amblyommatis (15) and AamCLE (39) were detected in 40 A. americanum, while the 74 A. maculatum only contained R. parkeri (30), "Candidatus Rickettsia andeanae" (3), and AmacFLE (74). Neither tick species had either Ehrlichia species. Consequently, we obtained no evidence for the frequent exchange of these tick-borne agents in a natural setting despite high levels of carriage of each agent and the common observance of infestation of both ticks on both dogs and humans at this site. Based on these data, exchange of these Rickettsia, Coxiella, and Francisella agents between A. maculatum and A. americanum appears to be an infrequent event.