Immune response to a recombinant capsid protein of striped jack nervous necrosis virus (SJNNV) in turbot Scophthalmus maximus and Atlantic halibut Hippoglossus hippoglossus, and evaluation of a vaccine against SJNNV

Abstract

Immunisation by intraperitoneal injection of an oil-emulgated recombinant partial capsid protein (rT2) from striped jack nervous necrosis virus (SJNNV) was performed on adult turbot Scophthalmus maximus and Atlantic halibut Hippoglossus hippoglossus. A specific humoral immune response was recorded in both species, and the levels of rT2-specific antibodies increased markedly in all groups during the 20 wk experiment. A challenge model for SJNNV was established by intramuscular injection of juvenile turbot. The turbot developed viral encephalopathy and retinopathy (VER), also known as viral nervous necrosis (VNN), with cumulative mortality in the range of 25 to 66%, after intramuscular inoculation with SJNNV propagated in the striped snake head cell line (SSN-1). Although neither clinical signs nor mortality were registered, SJNNV was neuroinvasive after bath exposure. The infection after both modes of challenge was verified by means of immunohistochemistry and RT-PCR, and SJNNV was reisolated in cell culture. The results indicate that SJNNV may have entered the central nervous system (CNS) by axonal transport through motor nerves after intramuscular inoculation. A vaccine efficacy test was performed on juvenile turbot, employing oil emulsified rT2 as a test vaccine and intramuscular inoculation of SJNNV. Significant protection was observed when the challenge was performed 10 wk post-vaccination. KEY WORDS: Viral encephalopathy and retinopathy (VER) · Nodavirus · Challenge model · Recombinant vaccine · Turbot · Atlantic halibut Resale or republication not permitted without written consent of the publisherDis Aquat Org 45: [33][34][35][36][37][38][39][40][41][42][43][44] 2001 The causative agents of VER are viruses belonging to the Nodaviridae (Mori et al. 1992, Comps et al. 1994. These viruses are unenveloped and icosahedral, with diameters of approximately 25 nm. Their bipartite genomes consist of single-stranded, positive-sense nonpolyadenylated RNA molecules, encoding the putative RNA-dependent RNA polymerase (RNA1) (Nagai & Nishizawa 1999) and the capsid protein precursor (RNA2) (Nishizawa et al. 1995).It has been demonstrated that the broodstock of some teleost species act as reservoirs of nodavirus by shedding viruses through gonadal fluids and infecting offspring (Mushiake et al. 1994, Yoshimizu et al. 1997. Prophylaxis of VER in striped jack Pseudocaranx dentex, barfin flounder Verasper moseri and Japanese flounder Paralychthys olivaceus has been attempted through prevention of vertical transmission by selection of non-carrier spawners identified by RT-PCR on gonadal fluids (Mushiake et al. 1994) or by serodiagnostic methods (Mushiake et al. 1993, Yoshimizu et al. 1997. Although prevention of the disease during larval and juvenile stages may be possible through broodstock management and disinfection of hatchery water, nodavirus in the environment may infect the fish when they are transferred to on-growing sites. Particularly in species whose adult fish are susceptible to VER, additional means ...

Serological relationships among genotypic variants of betanodavirus

“…Intramuscular injection of the recombinant RGNNV coat protein, which was expressed in Escherichia coli, induced neutralizing antibodies in the fish Epinephelus septemfasciatus and Chromileptes altivelis, and induced protection against challenge by RGNNV genotype viruses (Tanaka et al 2001, Yuasa et al 2002. A similar vaccine efficacy was obtained in juvenile turbot Scophthalmus maximus by intraperitoneal injection of an oil-emulsified recombinant coat protein from SJNNV (Húsgard et al 2001). The present immunization of kelp grouper with recombinant coat proteins demonstrated that anti-RGNNV and anti-BFNNV had cross-neutralizing activity against the heterologous RGNNV and BFNNV, but anti-SJNNV serum and anti-TPNNV serum neutralized only homologous virus (Table 5).…”

Betanodavirus of Marine and Freshwater Fish: Distribution, Genomic Organization, Diagnosis and Control Measures

“…To ensure that the fish are as healthy as possible, a useful and practical approach would be vaccination of fish and boosting their immune system. Various types of vaccines have been developed such as formalininactivated vaccine, subunit vaccine with recombinant coat protein of betanodavirus and nodavirus-like particle vaccine [58,74,111,116,118,121,124]. Vaccination trials have shown protection efficacy against betanodavirus infection.…”

“…Vaccination trials have shown protection efficacy against betanodavirus infection. For example, recombinant partial capsid protein of SJNNV [58] and AHNV [111] vaccinated turbot and Atlantic halibut fish are protected significantly against nodavirus challenge. Additionally, use of DNA vaccine based on the gene encoding for G protein of VHSV offers high but short term protection against the nodavirus infection [109].…”

Diseases, prophylaxis and treatment of the Atlantic halibut Hippoglossus hippoglossus: a review

“…The outbreak in Norway coincides with a decline in halibut fry production, and is probably the most important reason why Norway's production of halibut fry has been level since 1995. No vaccine is currently available, although the development of a vaccine has been initiated using the turbot Scophthalmus maximus as an animal model (Húsgar7 et al 2001). Outbreaks of VER in halibut, however, 61 Dis Aquat Org 48: [57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74] 2001 tend to occur at relatively early ontogenetic stages and before vaccination would be possible.…”