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.

Highlights

  • The ixodid ticks Amblyomma cajennense and Amblyomma dubitatum are the most frequent ectoparasites of capybaras (Hydrochoerus hydrochaeris) in Southeastern Brazil (VIEIRA et al, 2004; PACHECO et al, 2007)

  • 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

  • DNA sequences of 350-bp obtained from the gltA‐polymerase chain reaction (PCR) products of the four nymphal pools of Amblyomma spp. were identical to each other, and after Blast analysis, were shown to be closest (99.4%; 348/350) to the corresponding sequence of R. tamurae (AF394896), and second closest (99.1%; 347/350) to Rickettsia monacencis (DQ100163)

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Summary

Introduction

The ixodid ticks Amblyomma cajennense and Amblyomma dubitatum are the most frequent ectoparasites of capybaras (Hydrochoerus hydrochaeris) in Southeastern Brazil (VIEIRA et al, 2004; PACHECO et al, 2007). A. cajennense is a common parasite of horses, dogs, and various medium to large-sized wild mammals, and is the most common biting tick affecting humans in Southeastern and Central-Western Brazil as well (VIEIRA et al, 2004; GUGLIELMONE et al, 2006). Recent studies have reported that most of the BSF-endemic areas contain large populations of free-living capybaras, which act as primary hosts for both A. cajennense and A. dubitatum, and are exposed to rickettsial infection (HORTA et al, 2007; GUEDES; LEITE, 2008; PEREZ et al, 2008; SOUZA et al, 2008). It has been demonstrated that capybaras play an important role in the epidemiology of BSF, since they serve as a rickettsial source for creating new lineages of R. rickettsii-infected A. cajennense ticks (SOUZA et al, 2009)

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