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.

• Grant number: 23/01355-9
• Support Opportunities: Regular Research Grants
• Start date: July 01, 2023
• End date: June 30, 2025
• Field of knowledge: Agronomical Sciences - Veterinary Medicine - Preventive Veterinary Medicine
• Agreement: CNPq
• 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 research grant: 22/12852-0 - Ticks, Rickettsia and Borrelia: field and laboratory studies, AP.R
• Associated scholarship(s): 23/10324-0 - 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., BP.JD

Abstract

Argasid ticks can transmit microorganisms to their vertebrate hosts, which include humans. More specifically, some species of anthropophilic Ornithodoros transmit spirochetes of the genus Borrelia, which are the causative agents of Tick-Borne Relapsing Fever (TBRF). In South America, two species of this group were described in the first half of the 20th century. Among them, Borrelia venezuelensis, associated with the tick Ornithodoros rudis, has caused outbreaks of TBRF in Colombia and Venezuela. During the current century, B. venezuelensis was isolated from O. rudis in Maranhão state, and this isolate was designated as B. venezuelensis RMA01, which was cultured in vitro and its genome sequenced. The isolate of B. venezuelensis RMA01 was the only representative of a RFG Borrelia transmitted by Ornithodoros in South America, until recent efforts led to the animal isolation of a new spirochete named "Candidatus Borrelia caatiinga" from Ornithodoros cf. tabajara from the state of Pernambuco. Despite recent discoveries and advances, human infection with RFG Borrelia in Brazil remains unreported, possibly because it is a neglected and underdiagnosed disease. Since several species of Ornithodoros are parasitic to humans in Brazil, studies on vector competence and evaluation of infection dynamics are essential. In vitro culture and genome determination of the transmitted species of Borrelia spp. are also important. Based on this, the present study aims to expand the knowledge of relapsing fever epidemiology using experimental infections in the laboratory, in vitro isolation and genome determination of a Brazilian isolate of a relapsing fever group Borrelia sp. For this, the experimental infections will consist in evaluating and quantifying the trans-stadial perpetuation and transovarial transmission of "Candidatus Borrelia caatinga" in Ornithodoros cf. tabajara ticks and evaluating the vectorial competence of the different parasitic stages of the life cycle of this tick, using guinea pigs (Cavia porcellus) as animal model. From cryopreserved blood samples of guinea pigs infected with "Candidatus Borrelia caatinga", the in vitro culture of this agent in axenic medium (modified BSK: mBSK) will be performed and from this, the complete genome of this bacterium will be sequenced, for its subsequent description and publication as a valid species for Brazil. (AU)