Characterization of variable genomic regions of Indian white spot syndrome virus

A recent study examining genetic variations among the 3 completely sequenced white spot syndrome virus (WSSV) genomes isolated from China, Thailand and Taiwan revealed five major differences among them. Of these differences, a deletion region between ORF 23/24 and a variable region of ORF14/15 prone to recombination were of particular evolutionary significance. Focusing on these regions, 81 WSSV isolates from India were characterized by sequencing polymerase chain reaction (PCR) amplicons. The Indian strains carried a 10,970 bp deletion in the ORF 23/24 region relative to WSSV-TW and WSSV-TH-96-II. Analysis of the ORF 14/15 regions revealed two novel strains of WSSV with unique sequences which could have evolved by recombination. None of the WSSV isolates had a transposase sequence or VP35 gene as reported for Taiwan isolates. The Indian strains were closely related to Thailand strains suggesting movement of a putative ancestor from Thailand to other parts of the world including India.