Nucleotide sequences of the VP2 gene of eight infectious bursal disease viruses isolated from vaccinated chicken flocks in the northeast of China were determined. The sequence analysis showed that all of the isolates were also characterized by the vvIBDV conserved amino acid residues: 222A, 256I, 294I, and 299S. Four of them had one amino acid change (D-->N) at position 212 in VP2 major hydrophilic peak A, while two of the four isolates had another one (A-->V) at position 321 in major hydrophilic peak B. The other isolates were similar to the UK661 strain. Our findings demonstrated that the vvlBDV strains in the northeast of China could be diverse.
Infectious bursal disease virus (IBDV) is a birnavirus that causes immunosuppressive disease in chickens. Segment B of IBDV encodes the RNA-dependent RNA polymerase VP1, which is involved in virulence. We sequenced and analyzed segment B from seven Chinese IBDV isolates, all belonging to very virulent IBDV (vvIBDV), and clustered into Branches II and III. Phylogenetic analysis suggested that segment B of the HLJ isolates in Branch II might have originated from an unidentified host, and HuB-1 might have originated in Europe. Eight aa (4V, 61I, 145T, 287A, 508K, 511S, 646S, and 687P) were conserved in Branches II and III, and may contain potential segment B virulence determinants. Five aa (146D, 242E, 390M, 562P, and 695R) were found only in Branch III, and may be origin characteristics. Moreover, 55T and 63A in the 5'-untranslated region (UTR), and 2786C in the 3'-UTR were conserved in vvIBDV and may function in UTR secondary structure.
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