Search

Infectious bursal disease virus (IBDV), the etiological agent of infectious bursal disease (IBD), is a variable RNA virus of Avibirnavirus. Some artificially attenuated vaccine strains of IBDV can adapt to cell culture of chicken embryo fibroblast (CEF) cell or its immortalized cell line DF1 in vitro while wild-type IBDV cannot. In this study, for the first time, a naturally occurring cell-adapted classic strain (genogroup 1) of IBDV named IBD17JL01 was identified in China. Animal experiments showed that IBD17JL01 could severely damage the central immune organ of infected chickens. Sequence analysis of the full-length genome revealed the peculiar molecular characteristics of IBD17JL01 with a few amino acid substitutions that might be involved in cell-tropism, antigenicity, and virulence of IBDV. Identification of this novel strain is beneficial to our understanding of the complexity of the epidemiology of IBDV. And the expansion of viral cell-tropism might increase the potential risk of the reassortment of different IBDVs including the live vaccines., Competing Interests: Declaration of Competing Interest The authors declare that they have no competing interests., (Copyright © 2020 Elsevier B.V. All rights reserved.)

• Novel variant IBDV induced severe bursa lesions in chickens immunized with vvIBDV vaccines. • The antigenic mismatch between novel variant IBDV and vvIBDV was confirmed. • Key aa residues might be involved in antigenicity and virulence differences were analyzed. • Unique novel variant IBDV pathogenicity allows for the prevalence of atypical IBD. In recent years, atypical infectious bursal disease (IBD) with severe immunosuppression has brought new threats to the poultry industry and has caused considerable economic losses. Novel variant infectious bursal disease virus (IBDV) has been identified as the etiological pathogen and for unknown reasons is widespread in poultry on many chicken farms in China that have been immunized with vaccines against very virulent IBDV (vvIBDV). Using immunoprotection experiments in specific-pathogen-free chickens, we first verified that novel variant IBDV could severely damage the bursa of Fabricius of the important immune organ of immunized chicken in the presence of antibodies induced by three types of vvIBDV vaccines, which is a primary reason for the current epidemic of atypical IBD. Monoclonal antibody reactivity patterns and cross-neutralization assays further confirmed the obvious antigenic mismatch between novel variant IBDV and vvIBDV. Sequence analysis of the genome of novel variant IBDV (SHG19 strain) was performed and the key amino acid residues that might be involved in antigenicity and virulence differences of novel variant IBDV compared to vvIBDV were further analyzed. This study not only determined the primary reason for the atypical IBD epidemic, but also remind us of the urgency for developing new vaccines against novel variant IBDV. [ABSTRACT FROM AUTHOR]