Experimental transmission of a novel relapsing fever group Borrelia harbored by Ornithodoros octodontus (Ixodida: Argasidae) in Chile

Abstract

Tick-borne relapsing fever spirochetes of genus Borrelia thrive in enzootic cycles involving Ornithodoros spp. (Argasidae) mainly, and rodents. The isolation of these spirochetes usually involves a murine model in which ticks are feed and the spirochetes detected in blood several days later. Such an experiment also demonstrates that a given species of tick is competent in the transmission of the bacteria. Here, soft ticks Ornithodoros octodontus were collected in Northern Chile with the objective to experimentally demonstrate its capacity to transmit a Borrelia sp. detected in a previous study. Two guienea pigs (Cavia porcellus) were used to feed nymphs and adults of O. octodontus and the spirochetes in blood were inspected by dark-field microscopy and nested PCR. Although spirochetes were not seen in blood, DNA was detected in only one animal 11 days after ticks were fed. Genetic sequences of Borrelia flaB, clpX, pepX, recG, rplB, and uvrA genes retrieved from DNA extraction of positive blood were employed to construct two phylogenetic analyses. On the one hand, the flaB tree showed the Borrelia sp. transmitted by O. octodontus clustering with Borrelia sp.Alcohuaz, which was previously detected in that same tick species. On the other hand, concatenated clpX-pepX-recG-rplB-uvrA demonstrated that the characterized spirochete branches together with "Candidatus Borrelia caatinga", a recently discovered species from Brazil. Based on the genetic profile presented in this study, the name "Candidatus Borrelia octodonta" is proposed for the species transmitted by O. octodontus. The fact that spirochete was not observed in blood of guinea pigs, may 2 reflect the occurrence of low spirochetemia, which could be explained because the succeptibilitysusceptibility of infection vary depending on the rodent species that is used in experimental models. Although the vertebrate reservoir of "Ca. Borrelia octodonta" is still unknown, Octodon degus, a rodent species that is commonly parasitized by O. octodontus, should be a future target to elucidate this issue.

Isolation and molecular characterization of a novel relapsing fever group Borrelia from the white-eared opossum Didelphis albiventris in Brazil

“…detected in this study. This clade also exhibited a close relationship with “ Candidatus Borrelia octodonta”, recently reported infecting Ornithodoros octodontus in Chile ( Santodomingo et al, 2024 ). Based on this concatenated phylogenetic analysis, which supports that the new borrelial isolate corresponds to a putative new species, we propose the name “ Candidatus Borrelia mimona”, in allusion to the tick species ( O. mimon ) in which it was firstly reported by Muñoz-Leal et al (2021a) .…”

“…B. caatinga” ( Oliveira et al, 2023a ) and “ Ca . B. octodonta” ( Santodomingo et al, 2024 ). It is likely that this South American group of RFG Borrelia species have polymorphic loci or diverge genetically, since the primers designed using allochthonous species do not anneal.…”