Disease control efficacy of synthetic double-stranded RNA Poly(I:C) administration for viral nervous necrosis (VNN) in sevenband grouper ( Epinephelus septemfasciatus )

Nervous necrosis virus (NNV), the causative agent of viral nervous necrosis (VNN), is an indigenous virus in Korean coastal areas and a threat to the farming industry. In the present study, we investigated the curative and preventive effects against VNN in sevenband grouper (Epinephelus septemfasciatus) using polyinosinic polycytidylic acid [Poly(I:C)]. Fish challenged with brain-filtrates from VNN-affected fish at 0, 2, and 4d after Poly(I:C) injection showed <10% cumulative mortality, whereas fish that were not administered Poly(I:C) but challenged 14d after the Poly(I:C) injection showed 100% and 80% cumulative mortality, respectively. The surviving fish from the primary challenge with brain-filtrates following Poly(I:C) injection were highly protected from re-challenge at 15 and 30 d post-primary challenge. Moreover, fish pre-immersed with red-spotted grouper nervous necrosis virus (RGNNV) survived following Poly(I:C) administration, even though their clinical signs did not recover. From these results, it was confirmed that sevenband grouper were highly protected from RGNNV challenge by Poly(I:C) administration.