Serological evidence of Borrelia turicatae in Raccoons (Procyon lotor) from an endemic focus of tick-borne relapsing fever in Mexico.

Tick-borne relapsing fever is a neglected and overlooked disease. In Mexico, numerous historical reports document the distribution of Ornithodoros turicata, the vector of Borrelia turicatae, as well as human cases of infection. However, the enzootic cycle and reservoir hosts in Mexico remain unknown. Here, to detect previous infections with relapsing fever Borreliae in wild fauna a retrospective serological analysis was conducted with serum samples collected from raccoons trapped from 2022 to 2025 in the Navachiste region of Sinaloa, Mexico. Using a species-specific antigen, BipA from B. turicatae, and bacterial lysates of this spirochete, we found high exposure among this cohort (30/36 sera, 83.3%). These results indicate the role of raccoon in this area as frequent host of B. turicatae and, together with previous findings, suggest a possible endemic focus of tick-borne relapsing fever in northern Mexico. Our findings remark the need for further investigation into the ecoepidemiology of B. turicatae in this region.