Herbal medicines against avian infectious bronchitis virus: shared host-directed and multi-stage antiviral pathways

Avian infectious bronchitis virus (IBV) is a highly contagious and genetically diverse coronavirus that continues to pose a major threat to poultry production worldwide. Although vaccination remains the primary control strategy, the frequent emergence of viral variants and incomplete cross-protection among antigenically distinct strains necessitate complementary approaches for effective IBV management. Accumulating evidence suggests that traditional Chinese medicine (TCM) and herbal-derived compounds may provide protective benefits against IBV infection. Although certain herbal compounds directly target viral particles or life-cycle stages, many protective effects appear to involve host-directed regulatory mechanisms. Recurrent mechanisms include modulation of innate immune responses, particularly type I interferon signaling, together with regulation of inflammation, oxidative stress, apoptosis, autophagy, and stress-adaptive processes such as stress granule formation. In this narrative review, we searched PubMed, Web of Science, Scopus, Google Scholar, and major Chinese databases for studies related to IBV, herbal medicines, natural compounds, antiviral activity, and host-directed mechanisms. Direct IBV-specific evidence is available for only a subset of the interventions reviewed; findings from SARS-CoV, SARS-CoV-2, other non-IBV systems, and in silico analyses are treated as indirect and hypothesis-generating, and interventions supported solely by such findings are presented as candidates for IBV-specific validation rather than as established anti-IBV agents. We synthesize in vitro and in vivo evidence to identify recurrent host-response pathways and shared regulatory hubs, and propose a multi-target, multi-stage framework for the adjunctive use of herbal interventions in IBV control.