1. Changes in VP2 gene during the attenuation of very virulent infectious bursal disease virus strain Gx isolated in China
X W Zeng, C Y Fu, X M Wang, P Wei, H L Gao Avian Dis . 2004 Jan-Mar;48(1):77-83. doi: 10.1637/7061.
Very virulent (vv) infectious bursal disease virus (IBDV) Gx strain with high pathogenicity was attenuated through replication in specific-pathogen-free (SPF) chicken embryos and in chicken embryo fibroblast (CEF) cell cultures. The changes in VP2 nucleotide and the deduced amino acid sequences were obtained during attenuation of vvIBDV in CEF culture. Sequence analysis of selected passages from numbers 0 to 20 in CEFs (designated here Gx to CEF-20) showed that no changes were detectable in the VP2 gene before CEF-7. There were a few changes in the nucleotide sequence of the VP2 gene but no amino acid substitutions at CEF-8. The virus of CEF-9 was an intermediate with some amino acid changes that possibly were related to virulence. CEF-10 virus had become similar to CU-1 strain. The VP2 gene sequence remained the same from CEF-10 to CEF-20. The results of pathogenicity tests showed that the mortalities of Gx, CEF-5, CEF-8, and CEF-9 in 4-wk-old SPF chickens were 64%, 60%, 60%, and 32%, respectively; whereas CEF-10, CEF-15, and CEF-20 were nonpathogenic. Virus neutralization tests with Gx strain showed that the antigenicities are similar from Gx to CEF-20.
2. Changes in VP3 and VP5 genes during the attenuation of the very virulent infectious bursal disease virus strain Gx isolated in China
Houshuang Zhang, Yulong Gao, Honglei Gao, Xiaomei Wang, Chaoyang Fu, Yulin Ju Virus Genes . 2007 Jan;34(1):67-73. doi: 10.1007/s11262-006-0002-y.
A very virulent infectious bursal disease virus (vvIBDV) Gx strain with high pathogenicity was attenuated through replication in specific-pathogen free (SPF) chicken embryos and in chicken embryo fibroblast (CEF) cell cultures. The changes in nucleotide sequences and the deduced amino acid sequences of VP3 and VP5 genes during attenuation were obtained. Sequence analysis of selected passages from numbers 0 to 20 in CEF's (designated here Gx to CEF-20) showed that there were no amino acid changes detected in the VP3 and VP5 genes before CEF-9. There were some changes in the nucleotide sequence and amino acid substitutions in the VP3 and VP5 genes at CEF-9. CEF-9 was an intermediate with some amino acid changes which were possibly related to virulence. The amino acid sequences of VP2 and VP5 genes remained unchanged from CEF-10 to CEF-20. The results of pathogenicity test showed that the mortalities of vvIBDV-Gx, CEF-5, CEF-8, and CEF-9 were 64, 60, 60, and 28%, respectively, while there were no mortalities observed for CEF-10, CEF-15 and CEF-20. There was also no bursal atrophy when chickens were inoculated with CEF-10, CEF-15, and CEF-20. Virus neutralization tests with the Gx strain and sera from inoculated chickens showed that the antigenicity was similar from Gx to CEF-20. The implications of these findings for the study of IBDV virulence and a more effective control of vvIBDV are discussed.
