Total DNA extracted from shrimp showing histopathological changes characteristic of WSSV, MBV and HPV were used as templates for positive controls, and DNA extracted from healthy freshwater fish Labeo rohita was used as the template for the negative control. Amplification was carried out in a thermocycler (M. J. Research). The amplified PCR products were electrophoresed in a 1.2% agarose gel containing 0.5 µg ml–1 ethidium bromide, and visualized with a UVtransilluminator (Gel doc system, Hero Lab).