Molecular characterization of infectious bursal disease virus (IBDV) strains of genogroup A2B1 circulating in Delaware, Maryland, and Virginia from 2018 to 2023

< 0.05), suggesting that the substitutions could drive immune escape. Additionally, we detected amino acid substitutions in and around a key region of VP1 that correlates with virulence (residues 145-147), suggesting that different IBDV isolates could vary in pathogenic potential. Finally, 2/78 (2.5%) of the IBDV-positive bursal samples were also positive for avian reovirus (ARV), demonstrating that coinfection with multiple immunosuppressive viruses occurs in the field. These findings highlight the importance of ongoing IBDV surveillance.IMPORTANCEInfectious bursal disease virus (IBDV) causes a major immunosuppressive disease of poultry. Recently, new strains have emerged and spread in several countries. Ongoing surveillance in the US flocks is therefore critical to determine if any exotic strains of IBDV are circulating. The Delmarva region is a major US poultry-producing area; however, despite its importance, the last reported molecular characterization of IBDV isolated strains was in 2007. Here, we updated the molecular epidemiology of IBDV in the region and uncovered an amino acid signature in the consensus sequence of the capsid hypervariable region comprised of amino acid substitutions S215N, S317R, G322E, and E323D that drives viral escape from neutralizing antibody responses. These findings highlight the importance of ongoing IBDV surveillance and will help to better inform vaccine antigen selection to improve IBD control.