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Evaluation of the Rickettsia rickettsii infection interference on the genetic expression of eggs, larvae, and nymphs of the tick Amblyomma aureolatum (Acari: Ixodidae)


Spotted fever is an important disease caused by the bacteria Rickettsia rickettsii. Annually, this diseases is diagnosed throughout the American continent, where Brazil takes place with important endemic areas where lethality of the disease reaches 40% of the cases. R. rickettsii is a tick-borne-disease transmitted by Dermacentor, Rhipicephalus, and Amblyomma tick genus. The vector tick species in Brazil are the Amblyomma cajennense and Amblyomma aureolatum. R. rickettsia can survive through several tick generations, even tough, the prevalence of infected ticks in nature is lower than 1.5%. It is possible that this low Rickettsia prevalence is caused by its own pathogenic properties to ticks, since infected ticks show lower survival and reproduction rates. Thus, the molecular characterization of vector-rickettsia interaction is an essential point of studying, and potentially can generate data to clarify the Rickettsia pathogenic mechanisms to ticks, and clues about the enzootic uphold of R. rickettsii in nature. Literature data shows that R.rickettsii is more pathogenic to nymphs than to larvae and that the blood meal is a important step to Rickettsia reactivation inside the vector. In the other hand, data about the reactivation molecular process is quite unknown. This project aims to evaluate, for the first time, the genetic expression in eggs, larvae and nymphs of the tick Amblyomma aureolatum, with and without infection by R. rickettsii. A subsequent experiment will silence some of the tick genes expressed only in infected ticks, in order to evaluate their function in R. rickettsii transmission. This project will be developed alongside a parallel experiment using adult ticks of the A. aureolatum and A. cajennense species, and final data will be compared. We expect these studies result in data that may point for potential molecular targets for further studies on vaccine control. (AU)

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