White-toothed shrews (genus Crocidura) - small in size, but great in pathogen diversity

In this thesis, the role of European white‐toothed shrews as reservoirs for various known and previously unknown pathogens was investigated. A "reservoir" is defined as an animal that reproduces and excretes a pathogen without succumbing to disease. Shrews are a phylogenetically ancient, globally distributed and species‐rich group. Three subfamilies are distinguished: red‐toothed shrews (Soricinae), white‐toothed shrews (Crocidurinae) and African white‐toothed shrews (Myosoricinae). The three white‐toothed shrew species present in Central Europe, namely the lesser white‐toothed shrew (Crocidura suaveolens), bicolored white‐toothed shrew (Crocidura leucodon) and greater white‐toothed shrew (Crocidura russula) were studied together with the smallest recent shrew species, the Etruscan shrew (Suncus etruscus), which occurs in the Mediterranean region and is hold in captivity in Germany. The collection of shrews from Germany and additional European countries enabled a better portrayal of their current distribution, which is subject to fluctuations and only incompletely described. Leptospira kirschneri was detected in C. russula and C. leucodon and Neoehrlichia mikurensis‐DNA was obtained from C. russula for the first time. The absence of Coxiella burnetii, Brucella spp. and particularly arthropod‐borne pathogens (Anaplasma phagocytophilum, Bartonella spp., and Babesia spp.) may indicate a minor role of white‐toothed shrews in the transmission cycle of these pathogens possibly due to a shrew‐specific ectoparasite milieu. The virome of crocidurine shrews from Central Europe has not been studied previously. To characterise the virome, samples of the four crocidurine shrew species were analysed using high‐throughput sequencing. Several complete genomes of hitherto unknown viruses of the families Paramyxoviridae, Nairoviridae and Hepeviridae were detected. These viruses are phylogenetically closely related to globally occurring pathogens with health risks for humans and animals. In particular, the Hasua virus (Paramyxoviridae) is noteworthy due to its phylogenetic proximity to the zoonotic Langya virus, recently identified in China. In addition, the presence of Borna disease virus 1 (BoDV‐1) was detected for the first time in C. russula and C. suaveolens. Co‐infections with up to three of the discovered viruses were found in several shrews; co‐infections with the bacterial pathogens were not observed. Further research is required to determine the pathogenicity and zoonotic potential of the virus species discovered in this study. Extensive One Health‐concept based investigations were carried out in the municipality with the first human BoDV‐1 cluster. No anti‐BoDV‐1‐antibodies or BoDV‐1‐RNA could be detected in any of the human serum or nasopharyngeal swab samples, environmental samples and ticks. The resident’s questionnaire revealed likely contact to shrews and their excreta. An established ‘Citizen Science’‐project enabled the investigation of shrews and other small mammals. However, the presence of BoDV‐1 was exclusively detected in C. leucodon. Different BoDV‐1 variants, closely related to the BoDV‐1 sequences obtained from the deceased children, were phylogenetically identified in the municipality's C. leucodon population. Thus, the presence of BoDV‐1 and an existing shrew‐human interface could be confirmed beyond doubt. Future longitudinal studies will provide important information on the stability and transmission of BoDV‐1, which can be used for recommendations of preventive measures. Our data, together with additional multidisciplinary studies within the One Health‐concept assessing the biology and ecology of crocidurine shrews, will provide guidance to fully comprehend the shrew‐human interface and to promote sustainable co‐existence with these elusive, synanthropic species