Abstract
We compared the rickettsial infection status of Amblyomma cajennense ticks, humans, dogs, and horses in both Brazilian spotted fever (BSF)-endemic and -nonendemic areas in the state of Sao Paulo, Brazil. Most of the horses and few dogs from BSF-endemic areas had serologic titers against Rickettsia rickettsii antigens. In contrast, no dogs or horses from BSF-nonendemic areas had serologic titers against R. rickettsii antigens, although they were continually exposed to A. cajennense ticks. All human serum samples and ticks from both areas were negative by serologic assay and polymerase chain reaction, respectively. Our results indicate that surveys of horse serum are a useful method of BSF surveillance in areas where humans are exposed to A. cajennense ticks. In addition, we successfully performed experimental infection of A. cajennense ticks with R. parkeri.
Highlights
We compared the rickettsial infection status of Amblyomma cajennense ticks, humans, dogs, and horses in both Brazilian spotted fever (BSF)–endemic and –nonendemic areas in the state of São Paulo, Brazil
In all polymerase chain reaction (PCR) assays, DNA of A. cajennense ticks experimentally infected with R. parkeri yielded the expected bands whereas no bands were obtained for the negative controls
Our results for the nonendemic areas showed no evidence of a pathogenic Rickettsia species circulating in A. cajennense ticks in farms 4 to 6, since all animals, humans, and ticks were negative
Summary
We compared the rickettsial infection status of Amblyomma cajennense ticks, humans, dogs, and horses in both Brazilian spotted fever (BSF)–endemic and –nonendemic areas in the state of São Paulo, Brazil. We hypothesize that the absence of human cases of BSF in some areas of the state of São Paulo (where human parasitism by A. cajennense is intense) is related to the presence of other, less pathogenic Rickettsia species infecting A. cajennense tick populations. In this regard, our study evaluated the rickettsial infection status of A. cajennense populations from both BSF-endemic and -nonendemic areas in the state of São Paulo. We serologically evaluated humans and domestic animals from these BSF-nonendemic areas to compare it to a recent evaluation that we performed in BSF-endemic areas [17]
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