Fish immunization using a synthetic double-stranded RNA Poly(I:C), an interferon inducer, offers protection against RGNNV, a fish nodavirus

• Published in: Diseases of aquatic organisms 2008-01, Vol.83 (2), p.115-122
• Main Authors: Nishizawa, Toyohiko, Takami, Ikuo, Kokawa, Yuki, Yoshimizu, Mamoru
• Format: Article
• Language: English
• Subjects: Epinephelus septemfasciatus; Marine; Nodavirus
• ISSN: 0177-5103; 1616-1580

Viral nervous necrosis (VNN), caused by a fish nodavirus, is one of the most serious fish diseases worldwide. Here we report a unique vaccination method in sevenband grouper Epinephelus septemfasciatus using a synthetic double-stranded RNA polyinosinic polycytidylic acid (Poly(I:C)), an interferon inducer, followed by challenge with a live fish nodavirus. Fish injected with Poly(I:C) at 200 kg fish super(-1) were highly protected from artificial challenge with red-spotted grouper nervous necrosis virus (RGNNV) (relative percentage survival, RPS: 100%), and specific antibodies against RGNNV were detected in sera from survivors. Moreover, the surviving fish were protected from re-challenge with RGNNV (relative percent survival RPS: 100%). Thus, it was confirmed that specific immunity against RGNNV was established in sevenband grouper by injection with live RGNNV following Poly(I:C) administration. Antiviral state was induced in fish by injection with Poly(I:C) at =>50 kg fish super(-1), but no toxic response was observed in the fish even if Poly(I:C) was injected at a dose of 200 kg fish super(-1). In fish injected with Poly(I:C) at 200 kg fish super(-1), a high level of antiviral state of > 90% RPS against RGNNV challenge lasted for at least 4 d after Poly(I:C) injection. However, no curative effect by Poly(I:C) injection was observed in fish already infected with RGNNV. It is considered that the present immunization method using Poly(I:C) followed by a live virus injection could offer protection against various viral infections in a broader range of fish species.