Mapping Bornavirus encephalitis—A comparative study of viral spread and immune response in human and animal dead-end hosts

Borna disease virus 1 (BoDV-1) has long been recognized as a cause of fatal encephalitis in animals and was only recently identified as a zoonotic pathogen causing a similar disease in humans. This study provides the first comprehensive comparative analysis of BoDV-1-induced neuropathology in human and animal end hosts, including horses, sheep, and alpacas. Using immunohistochemical analyses, we investigated the topographical distribution of BoDV-1 and inflammatory responses in the central nervous system across 19 cases. Key findings reveal distinct differences and overlaps between humans and animals. While humans exhibited heterogeneous patterns especially of the lymphocyte infiltration, animals displayed more species-specific inflammation and viral spread patterns. In horses, the hippocampus and basal ganglia were consistently affected, whereas sheep showed predominant involvement of the frontal cortex and stria olfactoria. Alpacas demonstrated a less uniform distribution but highlighted the brainstem and basal ganglia as critical sites. Intriguingly, across all species, a negative association was observed between lymphocyte infiltration and the number of BoDV-1-infected cells. These findings enhance our understanding of BoDV-1 pathogenesis and is a first step of cross-species comparison in unraveling disease mechanisms in BoDV-1 infection. Further research is warranted to elucidate the implications of these findings for therapeutic strategies and to explore the entry and dissemination routes of BoDV-1 in different hosts.