Molecular detection of relapsing fever Borrelia puertoricensis in migratory Mexican free-tailed bats

Bats have been increasingly recognized to host relapsing fever borreliae as well as borreliae that form novel clades adjacent to the Lyme borreliosis group. However, the genetic diversity and zoonotic potential of bat-borne borreliae remain poorly understood, in part because most work to date has focused on bats in the tropics. Fewer bat-borne Borrelia surveys have been conducted in temperate zones, where many bats undertake seasonal migrations that may facilitate pathogen dispersal. We surveyed blood from nearly 400 Mexican free-tailed bats (Tadarida brasiliensis) during their seasonal occupancy in Oklahoma, USA, during 2022 and 2023, for Borrelia spp. Targeted PCR of the 16S rRNA and flaB genes revealed high nucleotide identity to Borrelia puertoricensis, and shotgun metagenomics further demonstrated high amino acid identity to strains isolated from argasid ticks and human blood. This represents the first detection of Borrelia puertoricensis in bats and only the second detection within wild vertebrate hosts. Infection prevalence was low but comparable to that of other borreliae in bats. Our findings suggest that Mexican free-tailed bats may contribute to the dispersal of this emerging tick-borne bacterial pathogen in North America.

Bacteria in the genus Borrelia are primarily spread by ticks and cause either Lyme borreliosis or relapsing fever. Substantial work has demonstrated the degree to which rodents and songbirds can contribute to the enzootic cycles and dispersal of these human diseases, but comparatively less attention has been paid to the role of wild bats, particularly in temperate regions. We here report human-relevant findings from a two-year, seasonal survey of migratory Mexican free-tailed bats (Tadarida brasiliensis) in Oklahoma, USA. We tested nearly 400 bats and identified Borrelia puertoricensis, a relapsing fever species that could infect humans. Importantly, this represents the first detection of Borrelia puertoricensis in bats and only the second detection in wild vertebrate hosts, expanding the known host range of this emerging tick-borne pathogen. Given the known migratory routes of Mexican free-tailed bats, our results have implications for the role that bats may play in tick-borne pathogen dispersal in North America.