Fernanda A Nieri-Bastos, Christopher D Paddock, Rita De Sousa, Arlei Marcili, Marcelo B Labruna
The bacteriumRickettsia parkerihas been reported infecting ticks of the 'Amblyomma maculatumspecies 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 ticksAmblyomma ovale, Amblyomma nodosum,andAmblyomma parvitarsum,respectively. These three strains are phylogenetically closely related toR. parkeri, Rickettsia africae,andRickettsia sibirica.Herein, we performed a robust phylogenetic analysis encompassing 5 genes (gltA, ompA, virB4, dnaA, dnaK) and 3 intergenic spacers (mppE-pur, rrl-rrf-ITS, rpmE-tRNAfmet) from 41 rickettsial isolates, including different isolates ofR. parkeri, R. africae, R. sibirica, R. conorii,and strains Atlantic rainforest, NOD, and Parvitarsum. In our phylogenetic analyses, all New World isolates grouped in a major clade distinct from the Old WorldRickettsiaspecies (R. conorii, R. sibirica, R. africae). This New World clade was subdivided into the following 4 clades: theR. parkerisensu stricto clade, comprising the type strain Maculatum 20Tand all other isolates ofR. parkerifrom North and South America, associated with ticks of theA. maculatumspecies complex; the strain NOD clade, comprising two South American isolates fromA. nodosumticks; the Parvitarsum clade, comprising two South American isolates fromA. parvitarsumticks; and, the strain Atlantic rainforest clade, comprising six South American isolates from theA. ovalespecies complex (A. ovaleorA. aureolatum). Under such evidences, we propose that strains Atlantic rainforest, NOD, and Parvitarsum are South American strains ofR. parkeri.ImportanceSince the description ofRickettsia parkeriinfecting ticks of the 'Amblyomma maculatumspecies complex' and humans in the New World, three novel phylogenetic close-related ricketsial 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 ofR. parkeri.Interestingly, each of theseR. parkeristrains seem to be primarily associated with a tick species group, namely,R. parkerisensu stricto with the 'A. maculatumspecies group',R. parkeristrain NOD withA. nodosum, R. parkeristrain Parvitarsum withA. parvitarsum,andR. parkeristrain Atlantic rainforest with 'A. ovalespecies group'. Such rickettsial strain-tick species specificity suggests coevolution of each tick-strain association. Finally, becauseR. parkerisensu stricto andR. parkeristrain Atlantic rainforest are human pathogens, the potential ofR. parkeristrains NOD and Parvitarsum to be human pathogen cannot be discarded.
