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Background   Rickettsia rickettsii , the etiological agent of Rocky Mountain spotted fever, is transmitted to humans by ticks. During tick feeding,  R. rickettsii  is exposed to both temperature elevation and components of the blood meal, which have previously been associated with the reactivation of its virulence. These environmental stimuli were also reported to modulate virulence genes of  R. rickettsii  infecting a set of organs of adult females of its natural vector,  Amblyomma aureolatum .    Methods  In this study, we determined the effects of a temperature upshift, blood-feeding, and both stimuli simultaneously on the expression of 85 selected genes of  R. rickettsii  infecting either the midgut (MG) or salivary glands (SG) of male and female  A. aureolatum  by microfluidic high-throughput RT-qPCR. These two organs are key for acquisition of this bacterium by the tick and transmission to the vertebrate host, respectively.    Results  Data showed that these environmental stimuli exert distinct effects on rickettsial transcription depending on the colonized organ and gender of the vector. Temperature upshift induced the majority of differentially expressed genes of  R. rickettsii  in tick SG, including tRNA synthetases encoding genes. On the contrary, blood-feeding downregulated most of differentially expressed genes in both organs, but induced type IV secretion system components and OmpB in tick MG. The combined effects of both stimuli resulted in a merged gene expression profile representing features of each stimulus analyzed independently, but was more similar to the profile induced by blood-feeding.    Conclusion  The upregulation of the majority of differentially expressed genes in tick SG by temperature upshift suggests that this stimulus is important to prepare  R. rickettsii  for transmission to the vertebrate host. Blood-feeding, on the other hand, induced important virulence genes in the tick MG, which might be associated with colonization of the tick and transmission to the vertebrate host. The role of the proteins identified in this study must be addressed and might help to define future targets to block tick infection, thereby preventing RMSF. To our knowledge, this is the first transcriptional tissue-specific study of a virulent strain of  R. rickettsii  infecting a natural tick vector.    Electronic supplementary material  The online version of this article (doi:10.1186/s13071-016-1581-7) contains supplementary material, which is available to authorized users.

parasites and vectors

Virulence genes of Rickettsia rickettsii are differentially modulated by either temperature upshift or blood-feeding in tick midgut and salivary glands