Effects of host diversity and the community composition of hard ticks (Ixodidae) on Babesia microti infection

Babesia microti (Apicomplexa, Piroplasmida) is one of the aetiological agents of human babesiosis, maintained in nature by complex zoonotic transmission cycles, involving sniall'wild mammals as hosts and hard ticks (Ixodidae) as vectors. We previously reported that the B. microti strain commonly encountered among Microtus rodents in Poland is not zoonotic and that it is therefore most unlikely that it represents a risk to public health. Here, we analysed the contribution Of Four rodent species, Myodes glareolus, Apodemus flavicollis, Microtus arvalis, and Mi. oeconomus as hosts for two species of locally abundant ticks (Ixodes ricinus and Dermacentor reticulatus) and the rodent infective B. microti. Studies were carried out in the Mazury Lakes District of north-eastern Poland in 2005 and 2006. Infestation prevalence and abundance of both species of ticks (altogether 5674) collected from 781 rodent hosts, including 61 A. flavicollis, 495 My. glareolus, 99 Mi. arvalis, and 126 Mi. oeconomus from two different habitats, were determined. A. flavicollis and My. glareolus from the woodland habitat were more frequently infested with larvae and nymphs of I. ricinus ticks (96.7% and 87.9%, respectively) than the other species of hosts. In contrast, a higher percentage (> 30%) of the other two species of rodents (Mi. arvalis, Mi. oeconomus) from fallow lands were infested with larvae and nymphs of D. reticulatus ticks (31.3% and 68.3%, respectively). Pronounced co-infestation rates (36.3%) of T ricinus; and D. reticulatus ticks (larvae and nymphs) were recorded on Mi. oeconomus. B. microti infections in blood samples of hosts and in ticks collected from hosts were examined by PCR, followed by sequence analysis. The prevalence of B. microti in hosts from the fallow lands (Mi. arvalis and Mi. oeconomus) was much higher than that in hosts from woodland (A. flavicollis and Mj,. glareolus). However, the overall prevalence of B. microti in ticks collected from rodents was quite low, and varied from 3.4% for larvae to 4.8% for nymphs of T ricinus and 11.8% for larvae to 4.0% for nymphs of D. reticulatus. The present study revealed for the first time the presence of B. microti DNA ill partly engorged immature L ricinus, but also in partly engorged larvae and nymphs of D. reticulatus. Furthermore, our results suggest widely differing roles of various rodent host species from two different habitats in maintaining zoonotic transmission of B. microti. (C) 2007 Elsevier GmbH. All rights reserved.