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

Abstract

AbstractTick-borne relapsing fever spirochetes of genusBorreliathrive in enzootic cycles involvingOrnithodorosspp. (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 ticksOrnithodoros octodontuswere collected in Northern Chile with the objective to experimentally demonstrate its capacity to transmit aBorreliasp. detected in a previous study. Two guienea pigs (Cavia porcellus) were used to feed nymphs and adults ofO. octodontusand 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 ofBorrelia flaB,clpX,pepX,recG,rplB, anduvrAgenes retrieved from DNA extraction of positive blood were employed to construct two phylogenetic analyses. On the one hand, theflaBtree showed the Borrelia sp. transmitted byO. octodontusclustering withBorreliasp. Alcohuaz, which was previously detected in that same tick species. On the other hand, concatenatedclpX-pepX-recG-rplB-uvrAdemonstrated that the characterized spirochete branches together with “CandidatusBorrelia caatinga”, a recently discovered species from Brazil. Based on the genetic profile presented in this study, the name “CandidatusBorrelia octodonta” is proposed for the species transmitted byO. octodontus. The fact that spirochete was not observed in blood of guinea pigs, may 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 byO. octodontus, should be a future target to elucidate this issue.