Genetic insights into circulating very virulent infectious bursal disease virus strains in Kenyan broiler flocks.

Infectious Bursal Disease (IBD), caused by Infectious Bursal Disease Virus (IBDV), remains a major threat to poultry industry worldwide, leading to immunosuppression, secondary infections, and resulting in economic losses. This study reports the molecular characterisation and phylogenetic classification of IBDV strains circulating in broilers from different Kenyan counties. Between 2022 and 2024, 44 broiler flocks (19-31 days old) suspected of IBD and vaccinated with an immunocomplex vaccine were sampled across six Kenyan counties. Bursal imprints on QIAcard FTA™ Classic were analysed by RT-PCR targeting the VP2 gene (segment A). Positive samples were further characterised by amplification and sequencing of the VP1 gene (segment B). IBDV was detected in 24/44 clinically suspected flocks (54.5%; 95% CI: 39.7-68.6%) submitted for molecular testing. Phylogenetic analysis revealed that 23 of these belonged to genotype A3B2 (very virulent IBDV, vvIBDV) and were closely related to strains circulating in Sub-Saharan Africa, while one detection matched the applied vaccine strain. Amino acid analysis confirmed conserved virulence markers in vvIBDV: A222, I242, Q253, I256, D279, I294, S299, and the serine‑rich heptapeptide SWSASGS (aa 326-332) in segment A, as well as the TDN motif (aa 145-147) in segment B. Unique African mutations (S254 and A/Q300 in segment A) were also identified. To our knowledge, this represents the first report on the molecular characteristics of IBDV strains circulating in Kenyan broilers. The predominance of vvIBDV highlights the persistent challenge posed by highly virulent strains in Africa, underscoring the need for continuous monitoring, enhanced biosecurity, and more effective vaccination strategies.