Multilocus Sequence Typing Unveils Two Novel Genospecies of Borrelia burgdorferi Sensu Lato in Ticks Infesting Cricetid Rodents of Northern Chile

Tick-borne spirochetes of the genus Borrelia are maintained in enzootic transmission cycles involving wild vertebrates such as rodents. The genus includes the lyme disease group (LDG), transmitted by hard ticks (Ixodidae), and the relapsing fever group (RFG), mostly transmitted by soft ticks (Argasidae). While research on Borrelia spirochetes has been largely concentrated in the Northern Hemisphere, recent studies have uncovered new genospecies in South American ecosystems. Particularly in Chile, while Borrelia chilensis is the sole species that has been cultured, multiple under characterized strains have been detected in wild rodents and ticks. This study aimed to genetically characterize strains of Borrelia in ticks parasitizing Phyllotis darwini, an abundant rodent species inhabiting the central north of the country. From 2021 to 2023, rodents were captured at two sites in the Coquimbo Region. Observed ticks were collected, morphologically identified, and submitted to DNA extraction to further detect the presence of Borrelia spirochetes through nested PCR targeting the flaB gene. Multilocus sequence typing (MLST) of eight housekeeping genes was subsequently performed on positive samples. Pairwise nucleotide comparisons and phylogenetic analyses with the retrieved sequences were conducted using maximum likelihood (ML) and Bayesian inference (BI) methods. A total of 634 P. darwini were captured, yielding 134 ticks, all identified as Ixodes spp. Ten ticks genetically identified as Ixodes abrocomae or Ixodes sigelos tested positive for Borrelia spp. Genetic identity and phylogenetic analyses revealed the presence of two novel LDG genospecies in Chile, where B. chilensis was the sole previously known species of the group. Although the vectors and pathogenic roles of these novel genospecies are currently unknown, our study underscores the need for further isolation attempts of the strains to assess their impact on wildlife or human health.