Genetic variability of tick-borne pathogens and their interactions

In Europe, sheep tick Ixodes ricinus is epidemiologically the most important vector. This tick species transmits a wide variety of zoonotic agents including Tick-borne encephalitis virus, bacteria, Anaplasma phagocytophilum, Rickettsia spp., Borrelia burgdorferi sensu lato spirochetes and protozoa Babesia spp. For estimating the risk of emerging zoonoses in Valle dei Laghi, Italy, we detected the presence of pathogens in nymphs and adult ticks, an important indicator of the hazard of infection. The highest prevalence of A. phagocytophilum and Rickettsia spp. were detected in ticks feeding on wild ungulates with 11.4% prevalence for both pathogens. For Babesia spp. and B. burgdorferi s.l. the highest prevalence was detected in ticks detached from birds, with 7.7% and 34.6% of positive ticks, respectively. Moreover, we analysed the intraspecific genetic variability. We were able to detect a wide range of tickborne pathogens, such as A. phagocytophilum, R. helvetica, B. afzelii, B. garinii, B. luisitaniae and B. valaisiana as well as pathogens not detected in Trentino before, such as; R. monacensis, R. raoultii, B. venatorum, B. microti, B. capreoli and B. turdi. In natural foci, wildlife vertebrates represent a significant element in circulation of tick-borne pathogens. Many of them are not only important hosts of ticks, but also reservoirs of pathogenic agents themselves. In order to determine the reservoir competence of the host, xenodiagnostic analyses must be performed however they are economically and ethically demanding. Therefore the ecology and transmission cycles of some tick-borne pathogens are still not completely understood. For this purpose we screened larval ticks detached from various hosts to provide relevant information on the potential reservoir capacity of a host. We have confirmed the importance of wild ungulates as reservoir hosts for A. phagocytophilum, birds as reservoir hosts for B. garinii, B. valaisiana, B. turdi and B. lusitaniae and rodents for B. afzelii. In order to clarify the importance of intra-specific genetic variability of A. phagocytophilum, we examined questing ticks, ticks detached from various hosts, blood and tissue from rodents in Italy and in questing ticks and engorged ticks detached from rodents from USA (South and North of USA) and Finland. Phylogenetic analyses of two loci revealed two distinct enzootic cycles of A. phagocytophilum in Europe. In addition to phylogenetic analysis of A. phagocytophilum, we focused also on B. burgdorferi s.l. genospecies, circulating in a given area. Individual genotypes were identified by molecular markers of the intergenic spacer and the four conserved genes used in MLST analysis. By use of these phylogenetic analyses, we were able to detect a new genospecies, B. turdi in Italy. Finally, by collaboration with partners from five different countries, we were able to determine acarological hazard of tick-borne pathogens in Europe. Remote sensing that included climatic and environmental data, together with statistical modeling revealed not only preferable habitat of I. ricinus but also countries and habitat types, that are more likely to experience higher transmission rate of tick-borne agents.