The Infectious Pancreatic Necrosis Virus (IPNV) and its Virulence Determinants: What is Known and What Should be Known

Abstract

Infectious pancreatic necrosis (IPN) is a disease of great concern in aquaculture, mainly among salmonid farmers, since losses in salmonid fish—mostly very young rainbow trout (Salmo gairdnery) fry and Atlantic salmon (Salmo salar) post-smolt—frequently reach 80–90% of stocks. The virus causing the typical signs of the IPN disease in salmonids, named infectious pancreatic necrosis virus (IPNV), has also been isolated from other fish species either suffering related diseases (then named IPNV-like virus) or asymptomatic; the general term aquabirnavirus is used to encompass all these viruses. Aquabirnaviruses are non-enveloped, icosahedral bisegmented dsRNA viruses, whose genome codifies five viral proteins, three of which are structural, and one of them is an RNA-dependent RNA polymerase. Due to the great importance of the disease, there have been great efforts to find a way to predict the level of virulence of IPNV isolates. The viral genome and proteins have been the main focus of research. However, to date such a reliable magic marker has not been discovered. This review describes the processes followed for decades in the attempts to discover the viral determinants of virulence, and to help the reader understand how viral components can be involved in virulence modulation in vitro and in vivo. There is also a brief description of the disease, of host defenses, and of the molecular structure and function of the virus and its viral components.

Low Pathogenic Strain of Infectious Pancreatic Necrosis Virus (IPNV) Associated with Recent Outbreaks in Iranian Trout Farms

“…IPN mortality rates were inconsistent at different farms and ranged from 50–60% (Hamedan) to 20–30% (Kurdistan) in fish of 1 g and 10g, respectively, confirming the age dependence of mortality caused by IPNV [ 7 , 10 , 34 ].…”

“…IPNV is a non-enveloped virus with a bi-segmented (A and B) dsRNA genome (~5 kbp) and belongs to the Aquabirnavirus genus within the Birnaviridae family [ 8 ]. Segment A encodes two viral structural proteins VP2 and VP3, the protease VP4, and a nonstructural protein, VP5 with indefinite function [ 7 , 9 , 10 ]. Segment B encodes VP1, a virion-associated RNA-dependent RNA polymerase [ 11 ].…”

Molecular Evolution of Infectious Pancreatic Necrosis Virus in China

“…However, phylogenetic analysis has not been performed on these Chinese IPNV isolates, and the genotypes of these previous Chinese IPNV isolates are still unknown. According to a previous study [ 41 ], all Sp serotype IPNV isolates belong to genogroup V, which suggests that the previous Chinese IPNV isolates likely to belong to genogroup V. Unfortunately, there is no available gene sequence to perform genotype analyses on the early isolated Chinese IPNV strains. Notably, the Chinese IPNV strains ChRtm213 [ 23 ] and WZ2016 [ 24 ], isolated in 2013 and 2016, respectively, belong to genogroup I not genogroup V, which raises many questions.…”

“…IPNV has a wide host range, such as rainbow trout [ 44 ] and Atlantic salmon [ 8 ]. It can also infect eels ( Anguilla anguilla ) [ 41 ] Atlantic cod ( Gadus morhua ) [ 45 ], Greenland halibut ( Sebastes mentella ) [ 45 ], deepwater redfish (S alvelinus alpinus ) [ 45 ], Arctic char ( Scophthalmus maximus ) [ 45 ] and pike ( Esox lucius L.) [ 46 ]. Because triploid rainbow trout is the main aquaculture species maintained in China, most of the fish samples tested in this study were from rainbow trout, and this species was the main host of the Chinese IPNV isolates.…”

Synthetic Peptides as a Promising Alternative to Control Viral Infections in Atlantic Salmon

“…IPNV is a double-stranded RNA non-enveloped virus, whose genome comprises two segments: segment A with two ORFs, the first one encoding the non-structural protein of 17 kDa VP5, and the second one encoding a polyprotein of 107 kDa, which after processing generates the proteins pVP2, VP3 and VP4 (54, 25 and 28 kDa, respectively); and segment B which encodes the RNA-dependent RNA polymerase, a protein of 97 kDa. Structurally the virion enclosing VP1, genomic RNA, and VP3 are assembled into an icosahedral capsid formed by VP2, and the initial step in the process of virus encapsidation seems to be the generation of VP2 (or pVP2) protein homotrimers, as building blocks [ 5 , 6 , 7 ].…”