Rickettsia bellii and Rickettsia amblyommii in Amblyomma ticks from the State of Rondonia, Western Amazon, Brazil

This study evaluates the rickettsial presence in Amblyomma ticks from eight areas of the Amazon forest in Rondonia, Brazil. The following tick species (number in parentheses) were examined: Amblyomna ovate Koch (121), Amblyomma cajennense (F.) (41), Amblyomma naponense (Packard) (36), Amblyomma scalpturatum Neumann (35), Amblyomma oblongoguttatum Koch (30), Amblyomma incisum Neumann (27), Amblyomma rotundatum Koch (16), Amblyomma coelebs Neumann (10), and Amblyomma humerale Koch (6). Ticks were examined individually or in pools (2-10 ticks) by polymerase chain reaction (PCR) targeting the gltA gene. The PCR-determined minimal infection rate for each tick species was A. ovale28%,A. cajennense27%,A. naponense0%,A. scalpturatum 11%, A. oblongoguttatum 3%, A. incision 0%, A. rotundatum 87%, A. coelebs 10%, and A. humerale 50%. Partial sequences of the gltA gene of Rickettsia from A. ovate, A. scalpturatum, A. oblongoguttatum, A. rotundatum, and A. humerale were 99.9% (349/350) identical to Rickettsia bellii. DNA sequences of PCR products from A. cajennense and A. coelebs were 100% (350/350) identical to Rickettsia amblyommii. R. bellii organisms were isolated in Vero cells from A. scalpturatum, A. ovate, A. rotundatum, and A. oblongoguttatum, but only one of the isolates, cultured from A. scalpturatum, was established in continuous cell culture passage. R. amblyommii was isolated from A. cajennense and was successfully established in continuous passage in cell culture. R. amblyommii infection of Vero cells was analyzed by transmission electron microscopy. This study adds South America to the known geographic distribution of R. amblyommii and reports rickettsiae in six Amblyomma species for the first time.