Introduction:Borrelia burgdorferi sensu lato (s.l.), the causative agent of Lyme borreliosis, is the most prevalent tick-borne pathogen in Europe, where it is mainly transmitted by Ixodes ricinus. This tick also circulates Borrelia miyamotoi, a member of the relapsing fever group of species. Objectives: A longitudinal study was performed to assess the prevalence of Borrelia spp. in questing ticks. Relationships between Borrelia prevalence in ticks and some variables such as tick development stage, sampling area, and questing tick density were assessed; in addition, the distribution of B. burgdorferi s.l. was analyzed to establish the periods of acarological risk. Methods: Ticks were collected monthly by flagging in three different ecological areas (coast, plateau, and mountain) in north-western Spain during a 2-year study. Borrelia DNA was detected by PCR, targeting the flagellin (fla) gene. Positive samples were also characterized at the rrfA-rrlB intergenic spacer region and the glycerophosphodiester phosphodiesterase (GlpQ) gene. Results:B. burgdorferi s.l. DNA was detected in 11.84% of I. ricinus. Five Lyme Borrelia species were identified (Borrelia afzelii, B. burgdorferi sensu stricto, Borrelia garinii, Borrelia lusitaniae, and Borrelia valaisiana). One single relapsing fever species (B. miyamotoi) was detected (0.85%). Questing Ixodes frontalis, Ixodes acuminatus, Dermacentor reticulatus, and Dermacentor marginatus yield negative results. The prevalence of B. burgdorferi s.l. was significantly higher in female ticks and in the mountain area. In addition, a seasonal pattern in the B. burgdorferi s.l. prevalence distribution throughout the study was not detected. Conclusions: The detection of a noticeable prevalence of B. burgdorferi s.l. in questing I. ricinus suggests a high acarological risk, especially in mountain area. There is no evidence of a relationship between the prevalence of B. burgdorferi s.l. and the density of questing ticks, nor traces of a seasonal pattern in the values of prevalence in ticks.
Keywords: Borrelia burgdorferi s.l.; Borrelia miyamotoi; Ixodes ricinus; longitudinal study; north-western Spain.