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Comparative of hematological parameters of naturally infected guinea pigs (Cavia porcellus), by ticks, by Rickettsia sp. strain Atlantic Rainforest against a secondary infection by Rickettsia rickettsii, agent of Brazilian Spotted Fever in humans

Grant number: 17/01708-8
Support type:Scholarships in Brazil - Scientific Initiation
Effective date (Start): August 01, 2017
Effective date (End): July 31, 2018
Field of knowledge:Agronomical Sciences - Veterinary Medicine
Principal Investigator:Felipe da Silva Krawczak
Grantee:Heytor Henrique Garcia Borges
Home Institution: Faculdade de Medicina Veterinária e Zootecnia (FMVZ). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

Brazilian spotted fever (BSF) is considered a reemerging disease in Brazil, showing a great impact on public health due to the difficulty of diagnosis and high lethality in cases not treated early, the lethality rate of this rickettsial disease in Brazil is between 30 and 40%. This disease is a zoonosis of an endemic features, caused by Rickettsia rickettsii and transmitted by arthropod vectors to man and other vertebrates. The ticks Amblyomma aureolatum and Amblyomma sculptum (published as Amblyomma cajennense) are the vectors of R. rickettsii for humans in Brazil. Recently, the presence of a new strain of human rickettsial disease belonging to the spotted fever group (SFG) has been reported in Brazil, unlike the others known rickettsial diseases worldwide, this new etiological agent has been named Rickettsia parkeri strain Atlantic rainforest. In these cases, no deaths were registred and the clinical signs presented a lower severity. Researchs demonstrated that the Amblyomma ovale tick is the vector of this new strain in Atlantic rainforest regions and that 3.6 to 16.7% of A. ovale ticks collected in areas of the Atlantic rainforest biome in the states of São Paulo (SP), Rio Grande do Sul (RS) and Santa Catarina (SC) were infected by Rickettsia sp. strain Atlantic rainforest. New studies developed in the USA and Costa Rica report interesting results where guinea pigs (Cavia porcellus) exposed to R. rickettsii didn't get sick or had rickettsemia when challenged previously by R. amblyommii. The Rickettsia spp. have cellular coating characteristics, which may give rise to cross-immunological reactions among of the SFG rickettsiae. Thus and of the risk caused by R. rickettsii, agent of BSF, presents to society, this study aims to evaluate if a first natural infection, by ticks, infected by Rickettsia sp. strain Atlantic rainforest would decrease hematological changes in guinea pigs (C. porcellus) against a secondary infection by R. rickettsii, and the results could be extrapolated to humans. (AU)