A Study On Pathogenic Biology And Molecular Epidemiology Of Infectious Bursal Disease Of Chickens In Jiangsu Province

Infectious bursal disease (IBD) is one of major contagious diseases that restrain healty development of the poultry industry in Jiangshu province which is a heavily concentrated broiler-producing areas. IBD outbreaks were continually observed in Jiangshu province although various vaccines have been used to prevent IBD. The appearance of antigenic variants or vvIBDV could be the reason for those field IBD outbreaks.In this study, we determined the nucleotide sequences of the coding regions for V?2 of 24 isolates. The nucleotide and deduced amino acid sequences of the 24 isolates were compared to the published sequences to identify the molecular determinants responsible for its virulents.1 By comparing the deduced amino acid sequences of the 24 IBDV isolates with other referencal sequences, the putative amino acid residues involved in the virulence were identified. Amino acid positions 249(K) and 254(S), which have been shown to be unique for variant IBDVs, and our 24 isolates exist 249(Q) and 254(G) at positions. 22 IBDV isolates exist 279(D) and 24 IBDV isolates exist 284(A).Four amino acid mutations conserved in very virulent isolates reported earlier at 222P-A, 256V-I, 294L-I and 299N-S were conserved in 24 isolates also. The serine-rich heptapeptide sequence "SWSASGS" adjacent to the second hydrophilic region was also conserved among 23 IBDV isolates.2 22 isolates had the Sspl site at position 1010 ,24 isolates present TaqI at position 832 and Styl site at position 887 and Nael site at position 983. 24 isolates lacked the Oral site , EcoRII site at poison 794 and BstNI at poison 796, which are similar to wIBDV.3 We compared the deduced amino acid sequences of the new 24 isolates with those of V?2 (AccI-Spel) from referencal isolates, and 24 isolates were most similar (91.7%-100%) to the wIBDVs. And identification of potential antigenic sites shows that 24 isolates were similar to the wIBDVs.4 Phylogenetic tree based on deduced amino acid sequence located in the hypervariable region ( AccI-Spel) of the VPa gene of studied and referential isolates indicates the studied isolates belong to wIBDV, and they were similar to the wIBDVs in Europe.5 At last, geographical distribution of pathogenic biology in Jiangshu province was completed.