Indian isolates of white spot syndrome virus exhibit variations in their pathogenicity and genomic tandem repeats

To detect genomic variation of white spot syndrome virus (WSSV) isolates from different geographical regions of India, the variable number of the tandem repeat (VNTR) region of the ORF 94 (Thailand WSSV isolate – GeneBank Accession No. AF369029 ) was analysed using five specific sets of primers. Analysis of 70 WSSV‐positive samples showed the presence of 14 different genotypes of WSSV with VNTRs ranging from 2 to 16 tandem repeats with the majority (85.47%) having 6–12 tandem repeats. Occurrence of different genotypes of WSSV was found to be neither correlated to any specific geographical region nor to the different growth stage of the tiger shrimp, Penaeus monodon. Pathogenicity studies conducted with 25 isolates of WSSV revealed the presence of virulent and avirulent strains of WSSV in Indian shrimp farms. However, an unambiguous link could not be established between the different genotypes and their virulence.