Open Access

More than half of the infectious diseases in humans are caused by zoonotic pathogens or pathogens of animal origin that were transmitted to humans a long time ago. Two important rodent-associated zoonotic pathogens are hantaviruses and human-pathogenic Leptospira spp. Both pathogens induce lifelong infection in the rodent hosts that shed the pathogen. Infection with these zoonotic pathogens in humans can cause clinical symptoms. Since some rodents, like the common vole (Microtus arvalis) and the bank vole (Clethrionomys glareolus syn. Myodes glareolus), have cyclic mass reproduction, this can result in years of population outbreaks in an increased number of disease cases in humans. This was found to be the case with the leptospirosis outbreaks in Germany and tularemia outbreaks in Spain, which were traced back to increased common vole density, as well as with the hantavirus disease outbreaks in several European countries, which were associated with bank vole population outbreaks. The aim of this work was to define the distribution and prevalence of different hantaviruses and leptospires as well as their coinfection in different European rodents, with a focus on voles from the genus Microtus and the identification of factors that affect the pathogen prevalence in rodent hosts. Therefore, common voles, bank voles, striped field mice (Apodemus agrarius) and other rodents were screened by molecular methods for the presence and prevalence of Leptospira spp. and different hantaviruses. Additionally, in selected studies, the presence of anti-hantavirus antibodies was screened by enzyme-linked immunosorbent assay (ELISA) using recombinant hantavirus-nucleocapsid proteins. The prevalence of hantavirus, Leptospira spp. and double-infections with both pathogens was analyzed using individual and population-based factors. Small mammals from four different European countries, Spain in the West, Germany and Austria in Central and Lithuania in Northeastern Europe, were included in the studies. With the molecular screenings, two new hantavirus strains were detected in continental Europe and were named Traemmersee hantavirus (TRAV) and Rusne hantavirus (RUSV) after the trapping locations in Germany and Lithuania, respectively. TRAV was detected in a field vole (Microtus agrestis) from the federal state of Brandenburg, Germany, while RUSV was detected in root voles (Microtus oeconomus) from Lithuania. Phylogenetic analysis of both hantaviruses indicates their close relation to Tatenale hantavirus and Kielder hantavirus, which were discovered in field voles in Great Britain. A pairwise evolutionary distance (PED) analysis showed that all four hantaviruses belong to the same hantavirus species, for which the putative name “Tatenale orthohantavirus” was proposed. Additionally, a recombinant RUSV antigen was generated and used successfully in ELISA for the detection of RUSV-specific antibodies and for the analysis of the cross-reactivity of monoclonal and polyclonal antibodies. In Germany, Tula orthohantavirus (TULV) was foremost detected in common voles in Thuringia and Brandenburg but was also detected in field voles in Brandenburg. Puumala orthohantavirus (PUUV) was detected in Thuringia at the virus distribution border, but sequences differed strongly from known sequences from another neighboring trapping location. While in Austria Dobrava-Belgrade orthohantavirus (DOBV), genotype Kurkino, was detected for the first time in striped field mice, no hantavirus RNA was detected in common voles from Spain. The cause of this absence in the Iberian common vole population might be its long-term isolation from the common vole populations more to the east. The TULV prevalence in Germany in this study was dependent on the season and on the prior growth of the reservoir population. An individual factor that affected the hantavirus prevalence, was the increasing age of the common vole. Leptospira spp.-DNA was detected in common voles from Spain and Germany, as well as in one striped field mouse from Austria. Except for the two detections of L. borgpetersenii in Spain, which were probably the result of spillover infections, only the genomospecies L. kirschneri was detected in common voles from Spain and Germany. The high prevalence of Leptospira spp., as well as the detection of only one genomospecies, confirm that L. kirschneri is the genomospecies for which the common vole is the main reservoir. Important factors for the Leptospira spp. prevalence were found to be, in addition to temperature and rainfall, the season and the preceding common vole density. Like the case with hantavirus, the age of the vole was found to be an influencing factor. In Germany, coinfections of TULV and Leptospira spp. were detected. These were associated with high common vole density and increased with the age of the common vole. Furthermore, the incidence of coinfections seems to be impacted more by the Leptospira spp. than by the hantavirus prevalence. As part of this thesis, TULV and PUUV were detected in previously untested regions in Germany, DOBV was detected for the first time in Austria and the distribution range of the putative species “Tatenale orthohantavirus” was extended to continental Europe for the first time with detection in two countries. Screenings in Spain indicate that certain common vole populations can be free from TULV infection. Furthermore, leptospires were detected in rodents from Spain, Germany and Austria. It was verified that certain Leptospira genomospecies are host-specific. Factors that influence the prevalence of infection or coinfection by hantaviruses and leptospires were determined. The origin and hosts associated with the Tatenale orthohantavirus should be clarified in further studies including the field vole and the root vole as well as other members of the genus Microtus in Europe and Asia. The development of a RUSV-antigen-based ELISA will enable future screening in humans and therefore might provide information about the human pathogenicity of this pathogen. For final confirmation of the zoonotic potential, isolation of the virus and development of a focus reduction neutralization test are necessary. The expansion of the striped field mouse to Austria and the detectable carryover of DOBV associated with this implies that further screening studies to more precisely characterize the distribution of DOBV (and other pathogens) are needed. The studies of DOBV spread in Austria as well as PUUV spread in Germany could help to better understand the emergence of zoonotic pathogens in new regions. The here described hantavirus-Leptospira spp. and Neoehrlichia mikurensis-Bartonella spp. coinfections should be further analyzed to characterize the interactions of the pathogens in the context of a microbiome and their influence on epidemiological aspects of the involved pathogens. The here identified individual and population-based impact factors for the TULV and Leptospira spp. prevalence should support the development and optimization of prediction models.