Sessions

Both rodents and insectivorous small mammals are considered to play a pivotal role in the epidemiology of tick-borne diseases, owing to their ubiquitous presence and support of – particularly immature – tick developmental stages, as well as playing a reservoir role of major tick-borne pathogens. The aim of this study was to examine this phenomenon, using Ixodes ricinus and Ixodes trianguliceps that were collected from small mammals in the period of 2014-2024 at the Grimsö Wildlife Research Station in central Sweden. Altogether 678 ticks, collected from seven species of 132 small mammals, were analyzed. These animals were selected based on their dual infestation with both I. ricinus and I. trianguliceps. On all host species, larvae predominated. Significantly higher proportion of I. trianguliceps larvae was observed in the autumn (94%) than in the spring (6%), when compared to I. ricinus larvae (autumn: 80%, spring: 20%). The infestation intensity was significantly higher in the case of I. ricinus larvae (mean: 3.5 ticks/host) than in the case of I. trianguliceps larvae (mean: 1.66 ticks/host). Concerning molecular-phylogenetic analyses, the Swedish cox1 haplotypes of I. trianguliceps clustered together with those form the UK, but at the same time separately from the Russian isolates. Babesia microti (non-zoonotic Munich strain) was detected in three ticks: two larvae of I. ricinus and a female of I. trianguliceps, all collected from bank voles (Clethrionomys glareolus). The DNA of zoonotic Babesia venatorum was present in two larvae and a nymph of I. ricinus from bank voles, as well as in a larva of the same tick species from common shrew (Sorex araneus). Twelve ticks, all I. ricinus (including a nymph and 11 larvae) were positive for borreliae. The borrelia-infected larvae originated from 10 host individuals on which all I. trianguliceps tested PCR- negative for borreliae. Sequencing identified seven genetic variants of Borrelia afzelii which phylogenetically did not show host species-related clustering pattern. In conclusion, the geographical pattern revealed by cox1 haplotypes of I. trianguliceps may have been related to genetic exchange (gene flow) and historical geographical connection via relevant host species between the UK and Scandinavia. While B. microti Munich strain was demonstrated in its less important vector, I. ricinus, B. venatorum and B. afzelii were not detected in non-vector I. trianguliceps. Our results attest that the epidemiological role of I. ricinus exceeds that of I. trianguliceps in maintaining the enzootic cycle of borreliae and zoonotic babesiae among small mammals.