High prevalence of Babesia microti 'Munich' type in small mammals from an Ixodes persulcatus/Ixodes trianguliceps sympatric area in the Omsk region, Russia.

Babesia microti is a genetically diverse group of protozoan parasites whose life cycle is associated with both small mammals and Ixodes spp. ticks. In this study, the prevalence of different B. microti genetic groups in ticks and small rodents in an area with Ixodes persulcatus and Ixodes trianguliceps occurring in sympatry was examined. A total of 541 small mammals were captured during eight sampling periods between 2013 and 2015 at a site in the Omsk region of Russia and tested for the presence of B. microti using nested PCR with subsequent sequencing of positive samples. B. microti DNA was found in 31.6 % of examined samples, and prevalence rates ranged from 5.3 to 61.6 % in different sampling periods. The sequenced B. microti samples belonged to two genetic groups: enzootic B. microti 'Munich' type and zoonotic B. microti 'US' type. B. microti 'Munich' type was more common across all sampling periods, with greater than 80 % prevalence in infected animals. Despite the high B. microti 'Munich'-type prevalence in voles, B. microti was not found in any of 394 adult I. persulcatus ticks collected by flagging or in the 84 I. persulcatus or 20 I. trianguliceps ticks taken from voles and molted under laboratory conditions. It was demonstrated that B. microti 'Munich'-type DNA can be detected in the blood of naturally infected voles for at least 20 weeks after capture. Thus, the high prevalence of B. microti 'Munich' type in small mammals may be explained by the prolonged persistence of B. microti in the blood of wild voles.