Infectious bursal disease virus (IBDV) causes a major immunosuppressive disease in chickens. In this study, we characterized the IBDV strains circulating in Delaware, Maryland, and Virginia (Delmarva) from 2018 to 2023. The sequence of the hypervariable region (HVR) of the VP2 capsid encoded by segment A, and a region of the VP1 polymerase gene encoded by segment B was obtained from 53 and 34 bursal samples, respectively. Phylogenetic analysis revealed that all the sequences belonged to genogroups A2 and B1, typical of US variant strains. An amino acid signature was identified in the HVR consensus sequence compared with the type-strain Delaware E (Del-E) consisting of amino acid substitutions S215N, S317R, G322E, and E323D. Strains with this signature were previously identified in 2007, in 25% of Delmarva IBDV sequences, and classified as clade two variants. Here, we found this signature had increased in prevalence and was present in 34/53 (64%) of the sequences from 2018 to 2023, including 13/17 (76%) of the sequences from 2023. The signature significantly reduced the virus neutralization titer of serum antibodies raised against Del-E (P < 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.
Egana-Labrin et al. (2026) studied this question.