Genetic profile and susceptibility of different Amblyomma sculptum tick populations to infection by Rickettsia rickettsia pathogen

Author(s)

Monize Gerardi

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina Veterinária e Zootecnia (FMVZ/SBD)
• Defense date: 2016-07-15

Examining board members

Marcelo Bahia Labruna; Fabio Gregori; Vanessa do Nascimento Ramos; Adriano Pinter dos Santos; Matias Pablo Juan Szabo

• Advisor: Marcelo Bahia Labruna

Abstract

Recently, the taxon Amblyomma cajennense taxon resulted in a systematic division, through morphological, molecular and biological studies. In Brazil, Amblyomma sculptum (belonging to the Amblyomma cajennense complex) has its importance in public health related to Rickettsia rickettsii transmission, the etiologic agent of spotted fever, disease that is considered the most important among the tick-borne diseases in Latin America. Brazilian Spotted Fever (BSF) has its occurrence in the southeastern region of the country where A. sculptum is well established and is almost always related to presence of capybaras. However, not all areas of southeastern of Brazil with A. sculptum ticks and capybaras have notifications of transmission of R. rickettsii to humans. This study aimed to evaluate, under laboratory conditions, the R. rickettsii susceptibility among six geographically distinct populations of A. sculptum. To this purpose, the transestadial perpetuation, transovarial transmission and possible deleterious effects of R. rickettsii infection were quantified in the six tick populations. In addition, we attempted to correlate the susceptibility to infection of different populations of ticks (from BSF-endemic and BSF-non-endemic areas) to the genetic profile of them through the markers mitochondrial 16S rDNA and nuclear ITS2. The results show differences in the susceptibility to infection with R. rickettsii among the six A. sculptum populations, although all populations were partially refractory to R. rickettsii infection. However, it was not observed any specific pattern of variation in biological and reproductive parameters of infected and uninfected ticks. Results of molecular characterization did not indicate genetic divergence between the populations for nuclear ITS2 marker. In the same way, analysis of mitochondrial 16S rDNA marker found no genetic differences that could be attributed to increased susceptibility or refractory of ticks to infection by R. rickettsii. However, it is note worth that nucleotide variability in this marker was observed among some populations, which seems to follow geographical patterns of origin. The exception to this result was the Belo Horizonte (Pampulha) population, which showed intrapopulation variability, having a similar genotype to the Grande Sertão Veredas population (GSV), both from the state of Minas Gerais and a second identical genotype to the Itu, from the state of São Paulo (AU)

• FAPESP's process: 13/14222-5 - Genetic profile and susceptibility of different populations of the tick Amblyomma sculptum to the infection by the pathogen Rickettsia rickettsii
• Grantee: Monize Gerardi
• Support Opportunities: Scholarships in Brazil - Doctorate