The Molecular Epidemiology Of The Isolates Of Infectious Bursal Disease Virus From Some Provinces Of China

Infectious bursal disease (IBD) is an acute, highly contagious viral infection of young chickens. Lymphoid cells, especially B cells, are the primary target cell and lymphoid tissue of the cloacal bursa is most severely affected. Severe prolonged immunosupression of chickens infected by the infectious bursal disease virus (IBDV) at an early age is posed, and the secondary infections of other pathogens (included bacteria or virus infections) are increased and vaccination failures are resulted.The purprose of the study is to make a molecular characterazation on the isolates of IBDV from the commercial chickens in some provinces of china. Fabricius' bursal, thymus and bone marrow collected from the provinces of Gangxi, Anhui, Jiangshu and Zhejiang in 2003-2006, were detected by a developed reverse transcriptase polymerase chain reaction (RT-PCR) technique for IBDV. Virul isolations were performed on the positive samples by chicken embryo inoculation via chorio-allantoic membrane (CAM) or cell culture with chicken embryo fibroblast (CEF). All the samples of died embryos or embryos with lesions and the cells with cytopathic effects (CPE) were detected routinely for bateria and HA, and the negative samples were then detected for IBDV by the RT-PCR technique. 20 isolates of IBDV were obtained in the study. The hypervariable region of VP2 gene (vVP2) of all isolates was analyzed by restriction enzyme analysis (REA) with Ssp â…  and Sac â…  . The results indicated that 10 of the isolates have the cleavage site of Ssp I but no the cleavage site of Sac â…  , belonged to very virulent IBDV (vvIBDV); the other 10 isolates have the restriction site of Sac â…  but no the restriction site of Ssp â…  , belonged to classical IBDV (cIBDV). The results demonstrated that IBDV infections have been popular in the commercial chicken flocks, and the prevalent isolates belonged to vvIBDV and cIBDV, but not variant IBDV (vIBDV).For study of the phylogeny and variations of critical sites in the genes of IBDV isolates, the vVP2 genes of 22 isolates and 5 commercial vaccine strains with intermediate virulent B87 (in), B87 (BJ), FW2512, Bursine-2, YSLMB...