Phylogenetic Evidence for the Existence of Multiple Strains of Rickettsia parkeri in the New World.

The bacterium has been reported to infect ticks of the " species complex" in the New World, where it causes spotted fever illness in humans. In South America, three additional rickettsial strains, namely, Atlantic rainforest, NOD, and Parvitarsum, have been isolated from the ticks , , and , respectively. These three strains are phylogenetically closely related to , , and Herein, we performed a robust phylogenetic analysis encompassing 5 genes (, , , , and ) and 3 intergenic spacers (, -ITS, and -tRNA) from 41 rickettsial isolates, including different isolates of , , , , and strains Atlantic rainforest, NOD, and Parvitarsum. In our phylogenetic analyses, all New World isolates grouped in a major clade distinct from the Old World species (, , and ). This New World clade was subdivided into the following 4 clades: the clade, comprising the type strain Maculatum 20 and all other isolates of from North and South America, associated with ticks of the species complex; the strain NOD clade, comprising two South American isolates from ticks; the Parvitarsum clade, comprising two South American isolates from ticks; and the strain Atlantic rainforest clade, comprising six South American isolates from the species complex ( or ). Under such evidences, we propose that strains Atlantic rainforest, NOD, and Parvitarsum are South American strains of Since the description of infecting ticks of the " species complex" and humans in the New World, three novel phylogenetic close-related rickettsial isolates were reported in South America. Herein, we provide genetic evidence that these novel isolates, namely, strains Atlantic rainforest, NOD, and Parvitarsum, are South American strains of Interestingly, each of these strains seems to be primarily associated with a tick species group, namely, with the " species group," strain NOD with , strain Parvitarsum with , and strain Atlantic rainforest with the " species group." Such rickettsial strain-tick species specificity suggests a coevolution of each tick-strain association. Finally, because and strain Atlantic rainforest are human pathogens, the potential of strains NOD and Parvitarsum to be human pathogens cannot be discarded.