In Europe, Ixodes ricinus tick is the vector of Lyme disease spirochetes and their relatives (Borreliella genus) and Borrelia miyamotoi. However, a newly described tick I. inopinatus with similar biological features and separated from I. ricinus may act as a vector for different Borrelia species. To date, eleven Borreliella species were detected in the natural populations of I. ricinus. Recently, two North American species have been detected in ticks parasitizing bats and red foxes in Europe, i.e., B. lanei and B. californiensis pointing to the necessity for searching for them in natural tick populations. In this study, using the coxI molecular marker only I. ricinus was identified in field-collected ticks with the exception of individual specimens of Haemaphysalis concinna. Using the flaB gene and mag-trnI intergenic spacer as molecular markers 14 Borreliaceae species have been detected with various frequencies in different parts of northern Poland. Among infected ticks, the most frequent were Borreliella (Bl.) afzelii (29.4%) and Bl. garinii (20.0%), followed by Bl. spielmanii, Bl. valaisiana, Bl. lanei, Bl. californiensis, B. miyamotoi, Bl. burgdorferi, Bl. carolinensis, Bl. americana, B. turcica, Bl. lusitaniae, Bl. bissettiae and Bl. finlandensis. Three of the above-mentioned species, i.e., Bl. lanei, Bl. californiensis and B. turcica were detected in this study for the first time in the natural ixodid tick population in Europe. The existence of the newly detected spirochetes increases their total diversity in Europe and points to the necessity of careful identification and establishment of the actual distribution of all Borreliaceae species transmitted by I. ricinus.

The western European hedgehog (Erinaceus europaeus) and the northern white-breasted hedgehog (E. roumanicus) are natural hosts of the tick Ixodes hexagonus, the vector of tick-borne pathogens such as the Borreliella bacteria responsible for Lyme disease. The aim of this study was to identify these pathogens in ticks collected from hedgehogs in northwestern Poland and to assess their genetic diversity by molecular analysis of the detected pathogens based on the flaB gene and the mag-trnI intergenic spacer. Among 101 hedgehogs examined, 737 ticks were found on 56 (55.45%) individuals, including 501 females of I. hexagonus. Borreliella spirochete infection was confirmed in 9 females of I. hexagonus (1.8%) obtained from 4 (3.96%) hedgehogs, detecting Borreliella (Bl.) afzelii (8/89%) and Bl. spielmanii (1/11%). Phylogenetic analysis based on the flaB gene and the mag-trnI intergenic spacer showed a lack of diversity in Bl. afzelii detected in I. hexagonus ticks collected from hedgehogs as well as little diversity against reference strains detected in small mammals and ticks collected from them. The results confirm that hedgehogs play an important role in the circulation of the detected spirochete species, at least as hosts of I. hexagonus ticks infected with them, indicating their potential to spread Borreliella spirochetes.

Monitoring the occurrence of Borreliaceae spirochetes in ticks may provide an indication of the risks of acquiring Lyme borreliosis (LB) and Borrelia miyamotoi disease (BMD). All ticks obtained in our study from humans in the years 2018–2022 (n = 1232) were identified morphologically for species, sex and developmental stage. The detection of Borreliaceae spirochetes and species identification were performed by nested PCR based on the flaB gene fragment and the region between the mag and trnI genes. Two species of ticks were identified: Ixodes ricinus (96.9%) and Dermacentor reticulatus (3.1%). The infection of I. ricinus ticks with Borreliaceae spirochetes was found to reach 18.3%, including B. miyamotoi (2.5%). Among Borreliella species, Bl. afzelii was the most frequent, followed by Bl. burgdorferi, Bl. spielmanii, Bl. valaisiana, Bl. garinii, Bl. bissettiae, Bl. californiensis and Bl. carolinensis. Borreliaceae spirochetes were also found in D. reticulatus ticks, of which Bl. afzelii and B. miyamotoi were the most common. In conclusion, ticks affecting humans in Poland represent a real risk of infection with Borreliaceae spirochetes, and knowledge of the prevalence and distribution of these bacteria is an important tool in assessing the risks of LB and BMD.