IS THE SMALL MAMMAL (CLETHRIONOMYS-GLAREOLUS) OR THE TICK VECTOR (IXODES-RICINUS) THE PRIMARY OVERWINTERING RESERVOIR FOR THE LYME BORRELIOSIS SPIROCHETE IN SWEDEN

We determined the capacity of bank voles (Clethrionomys glareolus) to infect feeding Ixodes ricinus ticks with Borrelia burgdorferi sensu la te (infectivity), during June to October 1991 and June to September 19 92 in south-central Sweden. In both years, the infectivity of older vo les to ticks was higher in August to September (48% to 59%) than in Ju ne to July (20% to 32%). We propose that the infectivity of bank vole populations in Sweden decreases during winter and spring due to death of highly infective voles and recruitment of uninfective young ones, a nd that the tick vector, rather than the mammalian host, is the primar y overwintering reservoir of B. burgdorferi.