Abundance of wild rodents, ticks and environmental risk of Lyme borreliosis: a longitudinal study in an area of Mazury Lakes district of Poland.

The results of a longitudinal epidemiological survey in two contrasting habitats in an area of the Mazury Lakes district of Poland indicate that both host and vector (Ixodes ricinus) densities, may be the most important risk factors for the tick-transmitted spirochetes of Borrelia burgdirferi s.l. However, the results also highlight that even related host species, such as the wild rodents Apodemus flavicollis and Clethrionomys glareolus that share the same habitat, can show quite different dynamics of tick infestation. We provide evidence that the woodland populations of A. flavicollis and C. glareolus are more frequently infested with larvae than nymphs, and more frequently with both stages than M. arvalis in the neighbouring open fallow lands. The prevalence of infestation with larvae varied from 92 % for A. flavicollis, and 76 % for C. glareolus to 37 % for M. arvalis. Other factors, such as population age structure and sex, were also shown to impact on tick densities on hosts at particular times of the year and hence on the zoonotic risk. Moreover, particular species of rodents from different habitats, A. flavicollis (woodlands) and Microtus arvalis (fallow lands) carry infected immature I. ricinus ticks more frequently than C. glareolus voles (woodlands). Thus, the relative contribution of each species to the cumulative reservoir competence differs among species living in the woodland habitats and in relation to voles living in the fallow lands. It follows, therefore, that any factor which reduces the relative density of A. flavicollis in comparison to other hosts in the wild rodent community, will reduce also the risk of human exposure to Lyme borreliosis spirochetes.