Borrelia circulating in soft ticks infesting colonial breeding seabirds along the Portuguese coast.

Seabirds are hosts of several tick species, but there is little information on their infestation by soft ticks and pathogens they harbour is available. In this study, we evaluated soft tick infestation in gull chicks from two breeding colonies in Portugal and assessed the prevalence of anti-Borrelia antibody in adults gull and shearwaters from these colonies, as well as from two additional urban colonies. The prevalence of infestation by Ornithodorus maritimus ticks in gull chicks varied between (17.6 %) in three yellow legged gull (Larus michahellis) and 84.8 % in the Audouin's gull (Ichthyaetus audouinii), with a mean infestation intensity of 4.50 ticks per infested yellow-legged gull chick and 5.59 ticks per infested Audouin's gull chick. All ticks, except one, were at the larval stage. Infestation prevalence was significantly higher at Deserta Island (south Portugal) compared to Berlenga Island. Of the 133 ticks screened, only two tested positive for Borrelia: one for Borrelia turdi (from a yellow legged gull) and one Borrelia mayonii from a Audouin's gull. However, only one gene could be sequenced for each. No relapsing fever Borrelia species were detected. Although differences among colonies were only marginally significant, Deserta Island exhibited higher anti-Borrelia antibody prevalence than Berlenga Island. No significant differences were observed between bird species. These findings highlights the need for further investigation into Borrelia- soft tick- seabird interactions, and the potential infection risks associated with gull breeding habitats, particularly in areas of human-wildlife contact.