Analysis Of Sequence Variability Among White Spot Syndrome Virus (WSSV) Isolates Within China

White spot syndrome virus (WSSV) is a major viral pathogen that causes high mortality in shrimp pond. It is a kind of large dsDNA virus, belongs to Nimaviridae family. So far three WSSV genome complete sequences originating from Taiwan, China and Thailand have been show on Genbank. By alignment of these three complete sequences, some variable loci in the genome have been mapped. They can be divided into deletions, variable numbers of tandem repeats (VNTRs), single nucleotide insertion/deletion and single nucleotide polymorphisms(SNPs).13 WSSV geographical isolates are used in this study. Special primers for the variable loci are set for PCR amplification. The sequence variability among these isolates have been made certain within the variable loci ORF23/24, ORF14/15 and putative transpasase, which are prone to deletion. The variable number of non-hrs unidirectional repeats of ORF75, ORF94 and ORF125 and the SNP in them also have been made certain. The result indicates that the origin of the Chinese WSSV isolates is multiple. The spread process of them is complex. They are mostly spread by man-made behavior. The variable loci evolve separately.The major type of nosogenesis-related gene of WSSV contains envelope protein gene, nucleocapsid protein gene, key enzyme gene of replication,putative cytokine receptor gene, latency-related gene and anti-apoptosis gene and so on. This study makes certain the variability within 8 nosogenesis-related genes and corresponding amino acid change among the Chinese isolates. The result show that single nucleotide polymorphisms, single nucleotide mutation and single nucleotide insertion happen in these genes. This result makes the foundation of studying the causation of the virulence difference among the geographical isolates.Polymerase chain reaction (PCR) is the major method in this study. In case of carry-over contamination, the dNTP mixture that dUTP takes the place of dTTP had been planed to used at the threshold of the study. But during the experiment, there seems to be a limitation of amplification size. The limitation then is found about 1400bp by more study. Product size in can expand of the length scope more long, the result is more unsteady, the appropriate Mg2+ concentration is lower. Due to the sequence variability among the isolates need to be accurately detected, dUTP is given up at last.