Research note: First report of very virulent infectious bursal disease virus in benin: Molecular characterization and implications for transboundary spread

Infectious bursal disease virus (IBDV) is an immunosuppressive disease pathogen that causes substantial economic losses to the global poultry industry. This study confirmed an outbreak of very virulent infectious bursal disease (vvIBD) in a 33-day-old broiler flock in the Republic of Benin, despite three prior vaccinations against IBD. The VP2 gene of the field vvIBDV strain in the outbreak farm was cloned, sequenced. Phylogenetic analysis revealed that the Benin field B123 shared the highest similarity with both the reference strain GHD1 from Vietnam (98.5 %) and the reference strain NN1172 from China (98.4 %). These three virus strains were located in the same evolutionary branch, displayed the closest genetic relationship, and all belonged to the very virulent IBDV (vvIBDV) strains. The close genetic relationship among the strains from Benin, China, and Vietnam suggests the possibility of transnational transmission events and highlights the global circulation of this vvIBDV lineage. Additionally, in the hyper-variable region of VP2 of isolate B123, there were amino acid residue markers of very virulent IBDV strains (222A, 242I, 256I, 294I, and 299S), however unique amino acid residue mutations or recombinations (187V and 430V) occurred in the conserved regions. Whether they are related to the protein's function remains to be further studied. This study provides important genetic data on vvIBDV circulating in West Africa and contributes to the global epidemiological understanding of IBDV evolution.