Zur @Bedeutung des Vektors Ixodes ricinus und verschiedener Wirtsspezies für die Verbreitung zeckenassoziierter Krankheitserreger
Spirochetes of the Lyme borreliosis group, Anaplasma phagocytophilum, rickettsiae of the spotted fever group (SFG) and parasites of the genus Babesia cause a great variety of partly life-threatening diseases. Although their importance as emerging tick-borne pathogens is increasing in Europe, many issues about their ecology are still unclear. To gain information about their transmission cycles, feeding and host-seeking Ixodes ricinus ticks were tested for pathogen-specific DNA. Bird-feeding ticks were more frequently infected with a variety of Borrelia spp. than small mammals, suggesting that rodents are less important as reservoirs for these pathogens. Surprisingly, two rodent-borne species were found in bird-feeding larvae whereas they were rare in ticks from small mammals. This suggests that the so far assumed strict associations of particular Borrelia spp. with different vertebrate species have to be rediscussed. For the first time, SFG-rickettsiae were detected in bird- and rodent-feeding ticks in Germany. Because rickettsiae are transmitted transovarially by I. ricinus, no conclusions about a reservoir role of examined host species can be drawn from the data but at least a vehicle function of migrating birds can be assumed. Furthermore, this study provides the first record of human pathogenic Babesia spp. in I. ricinus ticks collected from birds and rodents. The fact that not transovarially transmitted small Babesia spp. were found in larvae feeding on both vertebrate groups, suggests that they are competent reservoirs at least for Ba. microti. The data also indicate a reservoir function of small mammals for A. phagocytophilum. The presence of coinfected ticks in the investigation areas suggests that the risk for humans and animals of acquiring multiple infections is relatively high. Considering severe clinical outcomes as well as problems in diagnosis and treatment of coinfections, the guidelines for handling tick-borne diseases have to be updated.