Cloning and sequence analysis of the full-length genome of very virulent infectious bursal disease virus
In order to understand the genomic characteristics and genetic variation and strain type of infectious bursal disease virus(IBDV)isolate GZGY2022,which caused the death of chickens in Guizhou farm,primers were designed to amplify the whole genome of the isolate,and genetic evo-lution and strain type analysis were performed after cloning and sequencing.The results showed that the A and B segments of IBDV genome were 3 260,2 827 bp,respectively,encoding VP2-VP5 and VP1 genes.The nucleotide sequence homology between the A and B segments of this strain and the VvIBDV were 96.2％-98.7％and 87.7％-98.9％,respectively,which is the highest with NN1172 strain,83.1％-94.7％and 90.1％-91.0％with other strains.The results of genetic evolution and strain type study showed that IBDV strains can be divided into 6 branches according to antigen and virulence,and the A and B segments of the strain were clustered in the evolutionary branch of VvIBDV,and the strain was A3B3 genotype according to the new genotype classification method.The results of amino acid sequence analysis showed that there were 3 and 7 unique amino acid site variations in the A and B segments of the strain,respectively,and 13 unique characteristic amino acid sites in the coding region of the full-length genome were consistent with VvIBDV.The VP2 sequence of segment A has 19 characteristic amino acid identical with VvIBDV,among which hyper variable regions 222A,242I,253Q,256I,279D,284A,294I and 299S were characteristic ami-no acid sites of the VvIBDV,and the heptapeptide region sequence SWSASGS was consistent with the virulent strain.The VP1 sequence of segment B has 10 characteristic amino acid identical with VvIBDV,among which 61I,145T and 287A were the characteristic amino acid sites of the VvIB-DV.In addition,the nucleotide sequence GGTGCC of 777-782 did not form the restriction endo-nuclease site of Kpn Ⅰ,and combined with the triplet site 145/146/147(TEG),the segment B was consistent with the NN1172 strain,showed that its virulence was slightly weaker than that of the B2 strain of VvIBDV.The results of recombination analysis showed that there were no breaks and recombination sites in the sequence of the strain,and no recombination event occurred.In summa-ry,this study found that GZGY2022 strain belonged to the A3B3 genotype non-recombinant VvIB-DV strain,and its special amino acid sites were consistent with the molecular characteristics of VvIBDV.This study lays the foundation for further exploring the genomic characteristics and path-ogenicity of VvIBDV.
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