Rickettsia parkeri and “Candidatus Rickettsia andeanae” in Amblyomma maculatum (Acari: Ixodidae) collected from the Atlanta metropolitan area, Georgia, United States

Abstract

Rickettsia parkeri is a recently recognized human pathogen transmitted in the southeastern United States by Amblyomma maculatum, the Gulf Coast tick. Since R. parkeri was conclusively identified as a human pathogen in 2004, over 40 cases of R. parkeri rickettsiosis have been identified in the United States, most of which occur in the southeastern states. During 2012–2014, five of these cases were identified by a single urgent care practice in Coweta County, a Georgia county within the Atlanta metropolitan area. To investigate the occurrence of R. parkeri-infected A. maculatum in the Atlanta metropolitan area, ticks were collected from 6 counties around the city of Atlanta and evaluated for infection with a Rickettsia species. A total of 263 questing adult A. maculatum were collected during 2015 and 2016. Of these, 93 (35%) were PCR-positive for DNA of R. parkeri and an additional 46 (17%) were PCR-positive for DNA of “Candidatus Rickettsia andeanae,” a spotted fever group Rickettsia species of unknown pathogenicity. No co-infections of these two rickettsiae were detected; however four of the six counties sampled showed presence of both rickettsial organisms. The high frequency of R. parkeri in these tick populations indicates a potential risk for those living, working, or recreating in A. maculatum-infested habitats within these six counties in the Atlanta metropolitan area.