Analysis of variable genomic loci in white spot syndrome virus to predict its origins in Procambarus clarkii crayfish farmed in China.

Variable genomic loci were examined in 4 white spot syndrome virus (WSSV) isolates (08HB, 09HB, 08JS and 09JS) from Procambarus clarkii crayfish collected from Jiangsu and Hubei Provinces in China in 2008 and 2009. In ORF75, sequence variation detected in the 4 isolates, as well as in isolates sequenced previously, suggested that WSSV might have segregated into 2 lineages since first emerging as a serious pathogen of farmed shrimp in East Asia in the early-mid 1990s, with one lineage remaining in East Asia and the other separating to South Asia. In ORF23/24, deletions of 9.