The ecology of Ixodes trianguliceps ticks and their role in the natural foci of ixodid tick-borne borrelioses in the Middle Urals

From 1994 to 2011, over 7000 individuals of small mammals were captured and examined for ticks in the natural foci of ixodid tick-borne borrelioses (ITBB) in the Middle Urals (Chusovskoy District of Perm Territory). Alongside with the taiga tick (Ixodes persulcatus), which is the main Borrelia vector, approximately 5700 feeding individuals of Ixodes trianguliceps have been identified. The latter species has been found to be about five times less abundant than the former. I. trianguliceps has been collected from small mammals belonging to 19 species. Its main hosts are common shrews (Sorex araneus), bank voles (Clethrionomys glareolus), and northern red-backed voles (C. rutilus). I. trianguliceps shows two seasonal peaks of abundance, spring-summer, and summer-autumn. Plating in BSK II medium yielded 72 isolates of Borrelia from a total of 1142 individuals of I. trianguliceps; 64 isolates have been identified with PCR and RFLP. The mean values of the Borrelia infestation rate in I. trianguliceps larvae, nymphs, and adults are 2.6, 10.2, and 8.1%, respectively, which is 5–10 times lower than in the taiga tick individuals collected from the same mammals. Borreliae obtained from I. trianguliceps (as well as those from I. persulcatus) have been identified as Borrelia garinii and B. afzelii, the former spirochete species being more frequent (about 90% of isolates from I. trianguliceps). Our results indicate that I. trianguliceps ticks participate in circulation of the ITBB causative agents in the forests of the Middle Urals. Rare occurrence of the tick and low rates of its infestation with borreliae suggest that the species is unlikely to play a significant role in the epizootic development in the natural foci of ITBB.