Isolation and characterization of Bagaza virus: insights into host adaptability and zoonotic potential.

Bagaza virus (BAGV) is an emerging orthoflavivirus that primarily infects wild birds, but its ability to infect other hosts remains poorly understood. We isolated BAGV RNA from the brain of a dead red-legged partridge and evaluated viral adaptation and replication kinetics in avian, mosquito, mammalian, and human cell lines. BAGV replicated efficiently in monkey, mosquito, duck, and selected human cell lines (HEK-293T and Huh7.5), whereas replication was limited in other human, hamster, and chicken fibroblast cell lines, indicating variable cellular susceptibility. These differences may reflect host-specific adaptation or distinct innate immune responses. Viral RNA replication complexes localized to the cytoplasm, as shown by immunocytochemical detection of dsRNA. Ribavirin treatment significantly reduced viral titers and RNA levels, demonstrating antiviral sensitivity. Together, these findings provide new insights into BAGV biology, host adaptability, and potential zoonotic risk, and support the development of antiviral strategies and improved epidemiological surveillance within a One Health framework.