Repeatedly the shrimp culturing industry faces serious economic loss due to white spot disease caused by white spot syndrome virus (WSSV) in penaeid shrimp. The present study was carried out to determine the antiviral activity of traditional Indian medicinal herb Phyllanthus amarus against WSSV in freshwater crab, Paratelphusa hydrodomous (Herbst). For experimental challenge, crabs were injected with three different solvent extracts of P.Â amarus (aqueous, acetone and petroleum ether) along with WSSV. The efficacy of the extracts was confirmed by bioassay, histopathology and reverse transcriptase â polymerase chain reaction (RTâPCR). The overall results of the present study confirmed that acetone and petroleum ether extracts of P.Â amarus have significant antiviral effect against WSSV.