Comparison of the Missing Sequences of ORF14/15 and ORF23/24 of WSSV from Different Regions of China in 2014

Abstract:

White spot syndrome virus (WSSV) is one of the major pathogens that severely harm shrimp aquaculture. Different strains of WSSV display various virulence. In order to understand the geographic variation in fragments ORF14/15 and ORF23/24 of WSSV in China, we collected 48 samples of WSSV-infected shrimp from disease outbreak areas in 7 provinces of China between January and August in 2014. We identified the genotypes of WSSV-positive samples using PCR with ORF14/15 and ORF23/24 specific primers, and the amplified fragments were conjugated into T-vectors and transformed into the Top10 cells. We selected the positive clones and obtained their sequences. Then we compared the missing fragments of ORF14/15 and ORF23/24 from different samples with the sequences of TH-96-Ⅱ and China Taiwan strain (TW, AF440570) respectively. There were 21 samples with the products of ORF14/15 amplification, and 16 samples with the products of ORF23/24 amplification. The amplification ratios of ORF14/15 and ORF23/24 were 43.75% and 33.33% respectively. There were only 4 types of ORF14/15 compared to TH-96-Ⅱ. The lengths of the amplified fragments were 1260 bp, 1270 bp, 1892 bp and 2662 bp, corresponding to the missing 6540 bp, 6530 bp, 5908 bp and 5138 bp respectively compared to TH-96-Ⅱ. There were two types of ORF23/24 compared to the TW strain. The lengths of the amplified fragments were 1140 bp and 1146 bp, corresponding to the missing 12070 bp and 12064 bp respectively compared to the TW strain. These results suggested a certain degree of prevalence and variation of WSSV in China. There was an obvious difference in ORF14/15 between different strains，but only a minimal difference in ORF23/24. It is most likely that the variation in the missing fragments correlates with divergent WSSV virulence in different regions, and this notion needs to be further tested.