Ticks, Rickettsia and Borrelia: field and laboratory studies

• Grant number: 22/12852-0
• Support Opportunities: Regular Research Grants
• Start date: February 01, 2023
• End date: January 31, 2025
• Field of knowledge: Agronomical Sciences - Veterinary Medicine - Preventive Veterinary Medicine
• Principal Investigator: Marcelo Bahia Labruna
• Grantee: Marcelo Bahia Labruna
• Host Institution: Faculdade de Medicina Veterinária e Zootecnia (FMVZ). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated researchers: Adriano Pinter dos Santos ; Felipe da Silva Krawczak ; Job Lopez ; Luís Marcelo Aranha Camargo ; Sebastián Alejandro Munoz Leal
• Associated research grant(s): 23/01355-9 - Tick-borne relapsing fever in Brazil: studies from the Brazilian isolate "Candidatus Borrelia caatinga" for in vitro culture, bacterial genome and infection dynamics in the tick vector Ornithodoros cf. tabajara., AP.R

Abstract

The tick fauna of Brazil is composed of 77 species. Remarkably, 19 (25%) of these species have been discovered by science in the last 20 years, making Brazil the country with the largest number of new tick species described in the 21st century. In contrast to the vast knowledge about tick-borne diseases in the Northern hemisphere, in Brazil only two tick-borne zoonotic agents (Rickettsia rickettsii and Rickettsia parkeri, causing the spotted fever group of rickettsioses) have been confirmed. Despite increasing reports of new genotypes of bacteria and protozoa infecting ticks and mammals from different parts of Brazil, both the epidemiological cycle and the pathogenic role of these agents remain unknown. An important reason for this delay in knowledge is due to the unavailability of viable isolates of these agents under laboratory conditions. The general objective of the present project is to expand the knowledge of the diversity of ticks and bacteria of the genera Rickettsia and Borrelia in Brazil and of the epidemiology of spotted fever and borreliosis from experimental infections in the laboratory. To this end, the proposal has been divided into four subprojects. Subproject 1 aims to survey the tick fauna and its infection by Rickettsia spp. and Borrelia spp. in an area of western Brazilian Amazon, from where we recently received immature specimens of a new species of tick. The results will allow us to describe another tick species for the Brazilian fauna and may indicate the existence of potential tick-associated pathogens in the Amazon biome, serving as an alert for surveillance of vector-borne diseases in the region. Subproject 2 will evaluate, under experimental infections, the domestic pig (Sus scrofa) as a host amplifier of the Rickettsia rickettsii bacteria for the tick vector Amblyomma sculptum. Considering the increasing expansion of wild boar (S. scrofa) populations in Southeastern Brazil, including areas endemic to Brazilian spotted fever, the results of this subproject will allow us to infer whether these wild mammals may have some relevant role in the epidemiological cycle of spotted fever, and may highlight the effective risk of wild boars contributing to generate and disperse infected ticks within their geographical range. Subproject 3 will evaluate the vectorial competence and perpetuation of Borrelia venezuelensis infection in the different life cycle stages of the tick Ornithodoros rudis, from a colony of O. rudis found naturally infected recently in Brazil. Considering that B. venezuelensis is recognized as a pathogen for humans, the results of the present study will allow us to infer whether or not O. rudis can function as a vector of B. venezuelensis for humans in Brazil, as it does in other South American countries. In addition, the knowledge about the trans-stadial perpetuation and transovarial transmission of B. venezuelensis in O. rudis, as well as the possibility of horizontal transmission, will serve as basic subsidies for a better understanding of the ecology of this important spirochete of the relapsing fever group in Brazil. Finally, subproject 4 aims to establish in vitro culture of two new isolates of Borrelia spp. from the relapsing fever group in Brazil, and from this, to determine the genome of the two isolates and make their proper taxonomic descriptions as new species for Brazil. In vitro culture will also allow the isolates to be used in future work to develop diagnostic methods for relapsing fever in Brazil. (AU)