Molecular epidemiology of white spot syndrome virus in the world

After analyzing all the sequence information of ORF75, ORF14/15 and ORF23/24 of WSSV in the GenBank, the evolution of white spot syndrome virus (WSSV) in the world has been revealed. Based on the genotype of ORF14/ 15 variable region, WSSV has been divided into three groups: isolate originated from Thailand (WSSV-TH-96-II), isolate originated from India (WSSV-IN-07-I), and another Indian isolate (WSSV-IN-06-I), which are representative isolate of type I-clade, type II-clade and type III-clade respectively. According to the genotype of ORF75, two kinds of subtypes of WSSV have been established: isolates originated from Thailand (WSSV-TH and TH-96II), being the representative isolates of subtype I and isolate originated from China (WSSV-CN) and isolate originated from Taiwan (WSSV-TW), being the representative isolates of subtype IIa and subtype IIb respectively. The ORF23/24 variable region also could help us understand the spread of WSSV. Most strains of the WSSV were speculated to originate from somewhere in the Indian Ocean and then spread across the world. The source of the Australian WSSV (WSSV-AU) is still unclear.