Molecular characterization of very virulent infectious bursal disease virus strains circulating in Egypt from 2003 to 2014.

In the present study, four very virulent infectious bursal disease virus (vvIBDV) isolates from flocks of chickens with vaccination failure in Egypt in 2003, 2007, 2010 and 2014 were characterized. The four viruses, designated USC2003, USC2007, USC2010 and USC2014, were detected by reverse transcription PCR, subjected to sequencing of both genomic segments (A and B) and compared with geographically and phylogenetically diverse IBDV strains. Phylogenetic analysis of segment A (complete) and B (partial) revealed a close relationship between Egyptian and vvIBDV reference strains of European and Asian origin. The sequences of segments of A and B the current Egyptian isolates were 96.1-98.2% and 96.5-98.7% identical, respectively, to those of other known vvIBDV isolates. The deduced amino acid sequences of VP1, polyprotein (pVP2-VP4-VP3) and VP5 revealed the presence of putative virulence determinants of Egyptian isolates compared with vvIBDV and less virulent (classical and variant) strains. The Egyptian isolates also possess unique amino acids substitutions within the hypervariable region of VP2 that differ from those of other reference IBDV strains. Further studies may be necessary to determine the pathogenic significance of these amino acid substitutions to fully understand the molecular epidemiology and evolution of IBDV.