Determining the Dosage and Time of Injection for WSSV VP28 Double Stranded RNA to Penaeus indicus in Providing Effective Protection Against WSSV

Abstract

White spot syndrome virus of shrimp is best known for its wide distribution and high virulence in bringing mass mortality and huge economic loss to farmers. Though the virus has been causing widespread mortality to all the cultured penaeid shrimps for quite a long time, no effective treatment strategies have been identified so far. RNAi has been recognized as a powerful tool and found to be functional in shrimp. An attempt was made to verify the possibility of using this technology in the laboratory-based experiment through double-stranded RNA (dsRNA) construction and injection to Indian white leg shrimp, Penaeus indicus. Amongst the different dosages tried, 1 µg/gm of shrimp administered 24-48 hours before WSSV infection was found to be effective in providing full protection. While trying to further refine the time interval by injecting the shrimp with 1 µg of VP28 dsRNA/gm of shrimp at 3,6, 12 and 18 hours before WSSV infection, no protection was observed in any of these time intervals indicating that administration of dsRNA 24 hours before infection to be the most suitable. Real-time PCR analysis further indicated that only the shrimps injected with dsRNA 24 hours prior to infection were virus-free, and the others were with high copy numbers of WSSV. This experiment indicates that dsRNA can be used as a prophylaxis to further prevent the infection by WSSV.