Borrelia burgdorferi in rodents (Apodemus flavicollis and A. sylvaticus): duration and enhancement of infectivity for Ixodes ricinus ticks.

Ixodes ricinus is an important vector of Borrelia burgdorferi in Europe, and small rodents (Apodemus flavicollis, A. sylvaticus and Clethrionomys glareolus) are important sources for infecting ticks. In this study, we examined their reservoir role by studying the duration of their infectivity for ticks. A. flavicollis and A. sylvaticus mice captured in nature were exposed to uninfected I. ricinus larvae at different times after their capture: 10 days, and 2, 7, 11, 14 and 40 months. Ticks were examined for spirochaetes after moulting using direct immunofluorescence. All animals remained infective for ticks their life long but the efficiency of transmission from hosts to ticks varied from one individual to the other, presenting a three-fold variation (26.5% to 81.4%). Rodents continously exposed to successive infestations by larval I. ricinus ticks over a period of one month showed an enhancement of infectivity for larval ticks during this period.