Summary: | The prevalence of Borrelia burgdorferi s.l. in ticks collected from rodents and the ability of small rodents to transmit Borrelia pathogens to feeding ticks were estimated. 486 small rodents captured in Lithuania and Norway as well as 1210 Ixodes ricinus ticks and 307 Laelaps sp. mites collected on rodents were investigated. A total of 12.4% of immature I. ricinus ticks collected on rodents in Lithuania and 3.8% I. ricinus ticks collected on rodents in Norway were found infected with B. burgdorferi s.l. Microtus arvalis and Myodes glareolus in Lithuania were significantly more infested with infected larvae than Apodemus flavicollis mice captured in Lithuania and Norway. About 22% of the infested rodents in Lithuania carried infected ticks, and 6.9% of all rodents were infested with infected ticks. The highest percentages of infested hosts carrying infected larval and infected nymphal ticks were Mi. arvalis (40%) and My. glareolus (67%), respectively. In Norway, 12.5% of the infested A. flavicollis carried infected ticks, and 9.9% of all captured A. flavicollis were infested with infected ticks. 2.4% of larvae and 12.1% of nymphs feeding on A. flavicollis were infected. B. burgdorferi s.l. was not detected in any of 234 Laelaps sp. mites collected on rodents in Lithuania and 73 mites collected on rodents in Norway. According to calculated host-to-tick transmission coefficient (βH-T), Mi. arvalis and My. glareolus voles were found to be more efficient in transmitting B. burgdorferi s.l. to ticks than A. flavicollis mice, and the common vole Mi. arvalis was found to have the highest reservoir competence, higher than other captured rodent species. The genotyping of B. burgdorferi s.l. detected in feeding ticks from rodents collected in Lithuania and Norway revealed that the vast majority of the infections were caused by B. afzelii.
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