In-depth analysis of potential reservoir species for zoonotic Borna Disease Virus 1 (BoDV-1)

Lethal non-purulent myeloencephalitis of domestic mammals and humans can be caused by Borna disease virus 1 (BoDV-1, species *Mammalian 1 orthobornavirus*). So far, only the bicoloured white-toothed shrew (*Crocidura leucodon*) has been described as a natural reservoir of BoDV-1. The objective of this study was the characterization of BoDV-1 infections in putative reservoir hosts. Small mammals were collected all over central Europe. Primary screening of brain tissue for bornavirus RNA was performed using a BoDV-1-specific and a broad range panBorna RT-qPCR. Positive results were confirmed by partial or whole genome sequencing. For BoDV-1-positive individuals, viral antigen and RNA tissue distribution was analyzed via immunohistochemistry and RT-qPCR. Screening of about 9000 small mammals resulted in the detection of 28 BoDV-1 RNA-positive shrews (23/95 bicoloured white-toothed shrews [24.2%], 4/38 lesser white-toothed shrews, *Crocidura suaveolens* [10.5%] and 1/243 greater white-toothed shrew, *Crocidura russula* [0.4%]), all originating from known BoDV-1 endemic areas. All three species of shrews show a similarly broad viral RNA and antigen tissue tropism with the highest loads in neuronal tissue and lower amounts in non-neuronal tissue. Phylogenetic analysis of three human-derived BoDV-1 sequences matches sequences from shrews collected nearby residences of human cases, supporting the peridomestic infection risk.