Rickettsia species infecting Amblyomma ticks from an area endemic for Brazilian spotted fever in Brazil

Abstract

This study reports rickettsial infection in Amblyomma cajennense and Amblyomma dubitatum ticks collected in an area of the state of Minas Gerais, Brazil, where Brazilian spotted fever is considered endemic. For this purpose, 400 adults of A. cajenennse and 200 adults of A. dubitatum, plus 2,000 larvae and 2,000 nymphs of Amblyomma spp. were collected from horses and from the vegetation. The ticks were tested for rickettsial infection through polymerase chain reaction (PCR) protocols targeting portions of three rickettsial genes (gltA, ompA, and ompB). Only two free-living A. cajennense adult ticks, and four pools of free-living Amblyomma spp. nymphs were shown to contain rickettsial DNA. PCR products from the two A. cajennense adult ticks were shown to be identical to corresponding sequences of the Rickettsia rickettsii strain Sheila Smith. DNA sequences of gltA-PCR products of the four nymph pools of Amblyomma spp. revealed a new genotype, which was shown to be closest (99.4%) to the corresponding sequence of Rickettsia tamurae. Our findings of two R. rickettsii-infected A. cajennense ticks corroborate the endemic status of the study area, where human cases of BSF were reported recently. In addition, we report for the first time a new Rickettsia genotype in Brazil.