IPNV carrier Atlantic salmon growers do not express Mx mRNA and poly I:C-induced Mx response does not cure the carrier state

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

“…The fish challenged with RGNNV 0, 1, 2 and 4 d after the Poly(I:C) injection showed 95% or more survival rate, while the fish challenged 7 and 14 d after the Poly(I:C) injection showed 75 and 20% survival, respectively. It was thus considered that the antiviral state appeared just after Poly(I:C) injection and lasted for at least 4 d, but subsequently decreased and disappeared within 14 d. These results agree with previous experiments in salmonids and other fish species in which the fish Mx gene response following Poly(I:C) administration peaked 1 d after the injection, and subsequently disappeared within 15 d (Lockhart et al 2004, Purcell et al 2004, Plant et al 2005, Saint-Jean & Pérez-Prieto 2007, Fernandez-Trujillo et al 2008. It was noted that a high survival rate (95%) was observed in the fish receiving both Poly(I:C) injection and RGNNV challenge at the same time (Fig.…”

“…Subsequently, IFNs induce an antiviral state within multiple cell types. The antiviral mechanisms of IFNs and IFN-inducers have been reviewed previously (De Clercq 2006) and prophylactic treatment with Poly(I:C) offers protection in different fish models of virus infection (Jensen et al 2002, Lockhart et al 2004, Purcell et al 2004, Plant et al 2005, Saint-Jean & Pérez-Prieto 2007, Fernandez-Trujillo et al 2008.…”

Protection of rainbow trout from infectious hematopoietic necrosis (IHN) by injection of infectious pancreatic necrosis virus (IPNV) or Poly(I:C)

“…4B). These results agreed with previous data where Mx gene responses against Poly(I:C) peaked 1 d after the Poly(I:C)-injection in rainbow trout and Atlantic salmon, and subsequently disappeared within 15 d (Lockhart et al 2004, Purcell et al 2004. Similarly, the antiviral state against fish nodavirus induced by Poly(I:C)-injection lasted for a few days after injection in sevenband grouper Epinephelus septemfasciatus and subsequently decreased (Nishizawa et al 2009, this issue).…”

Infectious pancreatic necrosis virus suppresses type I interferon signalling in rainbow trout gonad cell line but not in Atlantic salmon macrophages

“…Nevertheless, following lysis of carrier macrophages, the virus replicates rapidly in CHSE cells and produces a CPE [25]. Furthermore, such carrier fish did not express Mx mRNA in liver, although they did so following injection of poly I:C without affecting persistence of the virus [14].…”

“…On the other hand, IPNV was shown to induce expression of Mx mRNA in rainbow trout head kidney cells in vitro [11]. In vivo, IPNV has been reported to induce IFN-like activity in rainbow trout fry serum [12]; Mx mRNA expression in Atlantic halibut tissues [13], and in Atlantic salmon post-smolts immediately following infection but not in IPNV carrier salmon [14]. These data suggest that IFN production and/or IFN signalling following infection with IPNV may be dependent on the type of cell infected or be a complex interaction between cells and the virus.…”