Sequence Comparison of WSSV Variable Regions from Different Parts of China in 2014

Abstract:

White spot syndrome virus (WSSV) is the most important and harmful pathogen in shrimp farming. As the areas and scales of prawn farming expand, more and more genetic variation in different WSSV strains has been noticed. Three regions of the WSSV variation located in ORF75, ORF94 and ORF125 of the genome, containing various numbers of tandem repeats (VNTR), and VNTR has been widely used as genetic markers in epidemiological studies. In this study we studied the molecular epidemiology of variation characteristics of WSSV in different areas of China. Forty-eight PCR-proved WSSV-positive samples were collected from Liaoning, Hebei, Shandong, Jiangsu, Zhejiang, Fujian and Guangdong during the white spot disease outbreak periods from January 2014 to August 2014. These samples were genotyped by PCR with specific primers of ORF75, ORF94, and ORF125, and the amplified fragments were then connected to T-vector and transformed into E. coli Top10. After the sequencing, we assayed the three WSSV VNTR regions in ORF75, ORF94 and ORF125 from different samples. The results confirmed 5 ORF75 VNTR types consisting of 4, 10, 11, 12 and 13 repeat units (RUs). We also identified 2 ORF94 VNTR consisting of 4 and 14 RUs, and 5 ORF125 VNTR consisting of 0, 3, 5, 6, and 7 RUs. The results suggested that there was a certain degree of prevalence and variation in WSSV in most parts of China, and that the variation in ORF75, ORF94 and ORF125 between different strains was obvious. Moreover, there could be a correlation between the specific VNTR variation and the disease outbreaks in different regions, which needs further investigation.