Comparison between genetic profiles of Amblyomma sculptum ticks from areas with and without circulation of Rickettsia rickettsii in the state of São Paulo

• Grant number: 24/06336-5
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: August 01, 2024
• End date: July 31, 2025
• Field of knowledge: Agronomical Sciences - Veterinary Medicine - Preventive Veterinary Medicine
• Principal Investigator: Marcelo Bahia Labruna
• Grantee: Carlos Eduardo Camargo Fanchini
• Host Institution: Faculdade de Medicina Veterinária e Zootecnia (FMVZ). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

The expansion of Brazilian spotted fever (BSF) transmission areas in the interior of the state of São Paulo has been associated with the population expansion of capybaras, the main amplifying hosts of the etiological agent of BSF (Rickettsia rickettsii) for the tick vector Amblyomma sculptum. However, many areas with the presence of capybaras and A. sculptum remain free of R. rickettsii, indicating that other factors may be involved in the establishment or not of R. rickettsii infection in ticks in a given area. In this sense, several studies suggest that genetic variations in vector populations affect the transmission of agents of many infectious and parasitic diseases at macrogeographic scales. Although A. sculptum is the only species of the Amblyomma cajennense complex identified in the Southeast region of Brazil, great genetic diversity has been reported among geographically distinct populations of this vector. Thus, it is reasonable to think that such genetic diversity may lead to differences in susceptibility to infection by R. rickettsii or in its maintenance over successive generations. Therefore, the present project aims to evaluate the genetic profile of A. sculptum tick populations in areas with and without circulation of R. rickettsii in the state of São Paulo, looking for differences that may be related to the transmission and propagation capacity of the bacteria by the vector. and thus in the establishment of the FMB. To this end, partial sequences of two A. sculptum mitochondrial genes, 16S rRNA and cytochrome oxidase II (COII), will be generated from adult specimens collected in 28 areas of the state of São Paulo, where the population of this tick is maintained primarily by capybaras. These 28 areas are previously confirmed as 15 areas with confirmed circulation of the bacteria R. rickettsii (endemic for BSF) and 13 areas considered free of circulation of the bacteria (non-endemic for BSF). The DNA sequences obtained will be analyzed in a parallel and independent manner for each mitochondrial gene, using haplotype diversity and affinity tests, geographic distance tests of A. sculptum populations, and phylogenetic analyses, always considering areas with presence and absence of R. rickettsii. The results obtained may generate inferences about a possible relationship between the genetic characteristics of A. sculptum populations and their vectorial capacity for R. rickettsii.