AFB1 promotes H3N8 replication in chickens by impairing gut colonization of protective segmented filamentous bacteria

<title>Abstract</title> AFB1, a common feed mycotoxin, can worsen viral infections. While H3N8 avian influenza mainly affects birds and can harm gut health, the combined impact of AFB1 and H3N8 infection on poultry intestines remains unknown. We show that environmentally relevant AFB1 levels (25–100 µg/kg) significantly enhance H3N8 replication in vitro and in vivo. Integrated histopathological, microbiome, and metabolomic analyses revealed AFB1-induced gut barrier dysfunction and specific depletion of beneficial bacteria (Eubacterium, Subdoligranulum), correlating with reduced dodecanedioic acid. Critically, AFB1 impaired ileal colonization of segmented filamentous bacteria (SFB), creating a permissive environment for viral propagation. Intervention with SFB supplementation reversed AFB1-mediated enhancement of H3N8 infection. Mechanistically, AFB1 disrupts intestinal homeostasis by compromising mucosal integrity and SFB colonization, thereby amplifying H3N8 pathogenesis. These findings establish a novel mycotoxin-virus interaction axis mediated through gut dysbiosis, underscoring the urgent need for AFB1 control strategies in poultry production to mitigate influenza risks.