Background: In the northeastern and midwestern regions of the United States Ixodes scapularis Say transmits the causal agents of anaplasmosis (Anaplasma phagocytophilum), babesiosis (Babesia microti), and borreliosis (Borrelia burgdorferi and B. miyamotoi). In the southeastern United States, none of those pathogens are considered endemic and two other tick-borne diseases (TBDs) (ehrlicihosis and rickettiosis) are more common. Our objective was to determine baseline presence and absence data for three non-endemic bacterial agents (Anaplasma, Borrelia and Babesia) and two commonly reported bacterial agents (Ehrlichia, and Rickettsia) in southern I. scapularis (n = 47) collected from 15 hunter-harvested white-tailed deer (Odocoileus virginianus) in western Tennessee.
Findings: Of the 47 ticks, 27 tested PCR positive for non-pathogenic Rickettsia species, two for Ehrlichia ewingii, one for Ehrlichia sp. "Panola Mountain", and one for Anaplasma phagocytophilum variant 1 strain. None of these ticks were positive for Babesia or Borrelia (including B. burgdorferi).
Conclusions: Finding human pathogens in host-fed I. scapularis merits additional studies surveying pathogen prevalence in questing ticks. Collection of questing I. scapularis in their peak activity months should be undertaken to determine the overall encounter rates and relative risk of pathogenic Ehrlichia in southern I. scapularis. Ehrlichia sequences were homologous to previous human isolates, but neither Babesia nor B. burgdorferi were identified in these ticks. With the identification of pathogenic bacteria in this relatively small collection of I. scapularis from western Tennessee, the study of the absence of Lyme disease in the south should be refocused to evaluate the role of pathogenic Ehrlichia in southern I. scapularis.