Data supporting the publication: Emergence of a Novel IBDV Subtype in Africa

The continuous evolution of infectious bursal disease virus (IBDV), especially the emergence of vaccine-resistant very virulent IBDV (vvIBDV) lineages, poses a critical threat to global poultry health and biosecurity. Here we conducted comprehensive surveillance of persistent IBDV outbreaks in vaccinated chicken flocks in Benin. Through molecular biological analyses, bioinformatic analyses and pathogenicity assays, we identified and designated a novel vvIBDV lineage A3aB5 for the first time, representing the first characterization of vaccine-escape vvIBDV in West Africa. This lineage is undergoing rapid adaptive evolution in West Africa, with a distinct evolutionary reservoir that markedly diverges from European and Asian strains. Signature amino acid mutations in VP2 (G254S, N280S/T, E300A, V384I) and VP1 (N145Q, E146D, D150E, D219E) drive substantial rewiring of conformational structure, surface electrostatic potential and Hydrophilic/Hydrophobic. These alterations underpin rapid adaptation to farming conditions and vaccine-mediated selection pressure, endowing the virus with robust environmental persistence, immune evasion and high pathogenicity, eliciting severe immune organ lesions (bursal atrophy/swelling and splenomegaly), and causing 70% mortality in cohabitation infection trials. Our findings uncover the molecular evolutionary hallmarks of this West African vaccine-escape vvIBDV, delivering actionable data for regional surveillance and precision control, while alerting the global poultry biosecurity framework to this urgent emerging risk.