Sequence analysis of the VP2 hypervariable region of nine infectious bursal disease virus isolates from Mainland China

The VP2 hypervariable region of infectious bursal disease virus (IBDV) from nine Mainland Chinese strains was amplified by reverse transcriptase/neste d polymerase chain reaction and cloned into pGEM-T vector. The nine isolate s, which were from the center (HN3), the north (Bj-1, B2/28, HD96), the eas t (JS-18 and AH-2), the northeast (D11-2, C4-2), and the west (Ts) of China , were sequenced and compared with each other and with six reference IBDV s equences. Clustering analysis separated the nine isolate into two groups. T he six virulent isolates, propagated in bursae, formed the first group. The y revealed only one to three amino acid changes from the very virulent (vv) European and Japanese isolates, suggesting that they might have die same o rigin as European and Japanese vvIBDV strains. On the basis of their distin ct geographic origins, extensive dissemination of vvIBDV in China was indic ated. (The other three chicken embryo fibroblast cell cultured isolates wit h mild pathogenicity were placed in the second group.) Their sequences corr elated closely with those of the culture-adapted strains (Cu-1 (4) and Cj-8 01). None of the nine isolates showed very close sequence relationship with the: antigenic variant strains from the USA. Although antigenic variants h ave been reported in China, the reverse transcriptase/polymerase chain reac tion-restriction endonuclease analyses of the nine viruses tested herein we re not similar to any U.SA. variant strains on the basis of computer softwa re analysis. Our results and conclusions agree with a previous molecular st udy of IBDV isolates from the south of China.