Evaluation of the bird Turdus sp as a competent host to amplify the bacterium Rickettsia rickettsii to Amblyomma aureolatum ticks in laboratory conditions

Abstract

Ticks are known as important vector of a great number of infectious agents. The fauna of ticks in Brazil is composed for 54 species, but only the Brazilian Spotted Fever and the Atlantic Spotted Fever are know as zoonosis transmitted by ticks throughout the country. The Brazilian Spotted Fever is severe disease to human being and is caused by the bacterium Rickettsia rickettsii which is transmitted in natural conditions by the bite of ticks from the genus Amblyomma, whereas in the Metropolitan area of the City of São Paulo, the vector is the tick Amblyomma aureolatum. Overall, the Rickettsia species related to ticks are kept among generations by transovarian transmission and transestadial perpetuation, nevertheless, it is know that to R. rickettsii, these strategies are less efficient, since the infection may diminish the reproductive parameters in tick females and may be even lethal to the arthropod. Therefore, the strategy of be perpetuated in the tick may not be strong enough for the bacterium survival. Transmission models have shown that vertebrate animal, natural tick hosts, may play an fundamental role in horizontal amplification of the bacterium R. rickettsii, even though, this role has never been studied for several tick host species, which include birds. Several bird species, remarkably the Brazilian Robin (Turdus sp), are known tick hosts for the subadult A. aureolatum tick phases, what may place birds as an important source of amplification to the bacterium R. rickettsii, in the other hand, this hypothesis has never been tested for South American birds. The potential role played by birds as Rickettsia amplifiers could be borne by systemic infection, when R. rickettsii spread all over the animal endothelial system and can be accessed by feeding ticks, other way the bacterium can be amplified is through the cofeeding phenomena, that has already been reported to ticks before, in this process susceptible ticks can be infected during by the blood meal even though there is no systemic infection in the host, in this situation infected ticks attach in a feeding site shared by non-infected ticks that ingest infected saliva released by the infected ticks. Regardless the importance of the horizontal amplification of R. rickettsii in ticks this hypothesis has never been tested in birds. This study will be carried out in order to test whether birds can amplify the bacterium to ticks and therefore might play an important role in Spotted Fever natural history. (AU)