Immunological findings of West Caucasian bat virus in an accidental host
The Lyssavirus genus includes seventeen neurotropic viral species which are able to cause rabies, an acute and almost invariably fatal encephalomyelitis of mammals. Rabies virus (RABV), the genus prototype, is a multi-host pathogen that undergoes multiple events of host-switching, thus occupying several geographical and ecological niches. In contrast, non-RABV lyssaviruses are mainly confined within a single natural host with rare spillover events never followed by adaptation to new accidental host species. In this scenario, unveiling the mechanisms underlying the host immune response against a virus is crucial to understand the dynamics of infection but also to predict the probability of colonization and adaptation to a new target species. Presently, the host response to lyssaviruses has only been partially explored, with the majority of data inferred from RABV infection, under the assumption that all members of the genus exhibit a similar behavior. Through our study we have investigated the immune response determined by the West Caucasian bat virus (WCBV). Indeed, WCBV has been recently associated with a spillover event to a domestic cat, raising concern about the risks for public health due to the circulation of the virus in its natural host. We selected the Syrian hamster as an animal model representative for an accidental host, and chose the intramuscular route in order to mimic the natural route of infection. In hamsters, WCBV was highly pathogenic, determining 100% lethality and mild encephalitis. In comparison with Duvenhage virus (DUVV) and RABV, we found that WCBV displayed an intermediate ability to promote cellular antiviral response, produce pro-inflammatory cytokines, recruit and activate lymphocytes in the hamsters central nervous system. Author SummaryViruses belonging to the genus Lyssavirus cause rabies, a zoonotic and almost invariably fatal encephalomyelitis. However, not all lyssaviruses behave in the same way, with Rabies virus (RABV) being a multi-host pathogen and non-RABV ones remaining mostly confined to their natural hosts. Host-pathogen interaction might help to elucidate the mechanisms behind the differences observed among lyssaviruses in terms of disease dynamics and ability to cross the species barrier, adapting to novel hosts. In our study, we have investigated the host immune response triggered by the WCBV strain spilled-over from its host (the bent-winged bat) to a domestic cat in 2020. Our study offers a key to understand and generalize the mechanisms underlying lyssavirus spillover and pathogenicity in accidental hosts. More generally, our work confirms and marshals previous, fragmentary evidence indicating a strong and inverse relationship between lyssavirus pathogenicity and immune response induction.