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 4 d after Poly(I:C) injection showed < 10% cumulative mortality, whereas fish that were not administered Poly(I:C) but challenged 14 d 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.

► We researched curative and preventive effects of Poly(I:C) for VNN in grouper.
► Fish injected with Poly(I:C) were highly protected from NNV challenge.
► Surviving fish, NNV challenged following Poly(I:C) injection protected NNV.
► Fish pre-immersed with NNV survived due to Poly (I:C) administration.