Abstract:In recent years, the fast development of aquaculture has been followed with the increased diseases such as the white spot disease to cause a great loss for the global aquaculture industry. To understand the variations in WSSV ORF14/15 and ORF23/24 and the VNTR in different regions of China in 2015, we investigated 57 samples WSSV-positive on PCR, collected in a disease outbreak area between April and October 2015. The tested samples were from Shandong, Guangdong, Hainan, Zhejiang, Tianjin and Jiangsu. Using specific primers, WSSV-positive samples were genotyped and the amplified fragments were ligated to a T-vector and transformed in Top10 cells. The positive clones were selected and sequenced. After sequencing, the fragments deleted from ORF14/15 and ORF23/24 in different samples were compared with the sequences of Th-96-Ⅱ and TW respectively, and three WSSV VNTR regions in ORF75, ORF94, and ORF125 from different samples were analyzed with the DNAMAN software. The results showed that 35 samples had the products of ORF14/15 amplification, and 14 sample had the products of ORF23/24 amplification. The lengths of the amplified fragments of ORF14/15 were 1270 bp, 1892 bp and 2075 bp, corresponding to deletions of 6530 bp, 5908 bp and 5725 bp, respectively, compared with Th-96-Ⅱ. One type of ORF23/24 was confirmed, and the amplified fragment was 1140 bp, corresponding to a deletion of 12070 bp compared with the TW isolate. Ten fragments were amplified from ORF75, including 1, 2, 3 repeat units with 45 bp, and 1 with 102 bp. Four different ORF94 VNTRs, including 4, 5, 10, or 12 repeat units, were identified. The ORF125 VNTR including 3, 5 or 6 repeat units was identified. The results showed that WSSV exhibited a significant difference in some open reading frames, but a significant stability in others.
