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.

Genetic heterogeneity among Vibrio alginolyticus isolated from shrimp farms by PCR fingerprinting.

AIMS: To study the strain variability among Vibrio alginolyticus isolates from different sources by insertion sequence-targeted PCR fingerprinting and whole cell protein profile analysis. METHODS AND RESULTS: Eleven strains of V. alginolyticus were isolated from seven different sources including healthy, infected, farm-reared and wild shrimps. Following biochemical characterization, the isolates were analysed by PCR fingerprinting and whole cell protein analysis by SDS-PAGE. The strains were genetically different irrespective of the sources of isolation. CONCLUSIONS: Strain variation exists in V. alginolyticus isolates obtained even from the same source, and PCR fingerprinting is a simple and efficient method in identifying strain-specific variations among the different isolates. SIGNIFICANCE AND IMPACT OF THE STUDY: Vibrio alginolyticus is implicated in severe vibriosis of marine aquaculture systems although many strains are avirulent and could be used as probiotic strains. As a wide variation exists among this species, differentiating the harmful and beneficial strains would help in finding ways of controlling the infections by eliminating harmful shrimp pathogenic vibrios.