Infectious pancreatic necrosis virus in fish by-products is inactivated with inorganic acid (pH 1) and base (pH 12).

The aquaculture industry needs a simple, inexpensive and safe method for the treatment of fish waste without heat. Microbial inactivation by inorganic acid (HCl) or base (KOH) was determined using infectious pancreatic necrosis virus (IPNV) as a model organism for fish pathogens. Salmonella and spores of Clostridium perfringens were general hygiene indicators in supplementary examinations. IPNV, which is considered to be among the most chemical- and heat-resistant fish pathogens, was reduced by more than 3 log in 4 h at pH 1.0 and pH 12.0. Salmonella was rapidly inactivated by the same treatment, whereas spores of C. perfringens were hardly affected. The results indicate that low and high pH treatment could be particularly suitable for fish waste destined for biogas production. pH treatment at aquaculture production sites could reduce the spread of fish pathogens during storage and transportation without disturbing the anaerobic digestion process. The treatment could also be an alternative to the current energy-intensive steam pressure sterilization of fish waste to be used by the bioenergy, fertilizer and soil improver industries.

Pancreas disease (PD) in sea-reared Atlantic salmon, Salmo salar L., in Norway; a prospective, longitudinal study of disease development and agreement between diagnostic test results.

A prospective longitudinal study was performed on three cages at each of three Norwegian Atlantic salmon seawater sites that experienced outbreaks of pancreas disease (PD). Once salmonid alphavirus (SAV) ribonucleic acid (RNA) was detected by real-time RT-PCR (Rt RT-PCR) at a site, it became detected in all studied cages and was persistently found until the end of the study period up to 19 months after first detection. SAV-specific antibodies were detected at all sites until the end of the study period and were also found at a high prevalence in broodfish at the time of stripping. No evidence of increased viral activity was detected in these broodfish. One site tested negative over several months prior to the first detection of SAV by Rt RT-PCR and SAV-specific antibody, which occurred 1 month prior to clinical manifestations of PD. Moribund fish or thin fish/runts that were sampled after the first PD diagnosis had almost twice the risk of testing positive by one or more diagnostic tests compared to that of randomly selected apparently healthy individuals. This paper describes the first detailed investigation of the disease development of PD at site and cage level in Norway, as well as an assessment of the performance and agreement of the commonly used diagnostic tests.

A sequential study of pathological findings in Atlantic halibut, Hippoglossus hippoglossus (L), throughout one year after an acute outbreak of viral encephalopathy and retinopathy.

Following a natural outbreak of viral encephalopathy and retinopathy (VER) at a commercial farm in Norway, surviving Atlantic halibut, Hippoglossus hippoglossus, were sequentially studied for distribution of nodavirus, immune response and histopathology over 1 year. Typical clinical signs and histopathology of VER were observed during the acute stage of the disease. Most of the surviving fish became subclinical carriers of nodavirus with clusters of nodavirus-containing cells in the central nervous system. Four random samplings of presumably healthy fish were performed from two fish groups, with low and high growth rates respectively, over a 7-month period. Immunohistochemical (IHC) examination revealed a higher number of nodavirus-positive cells in fish with a low growth rate than in fish with a high growth rate. All IHC positive fish were also reverse transcriptase polymerase chain reaction (RT-PCR) positive for nodavirus and for nodavirus antibodies detected by enzyme-linked immunosorbent assay (ELISA) at all sampling points. The percentage of PCR- and ELISA-positive fish remained high throughout the year, while the number of IHC-positive fish decreased, especially in the group with a high growth rate. Several other histopathological changes were observed, including pericarditis, steatitis, changes in liver and kidney, and necrosis of the intestinal wall. None of these findings seemed to be related to the nodavirus infection. Nodavirus was reisolated in cell culture from subclinically infected fish one year after the acute VER outbreak, which indicates that the virus was still infectious.

Isolation in cell culture of nodavirus from farmed Atlantic halibut Hippoglossus hippoglossus in Norway.

Isolation in cell culture of nodavirus from Atlantic halibut Hippoglossus hippoglossus suffering from viral encephalopathy and retinopathy (VER) is described. The cell line SSN-1 was inoculated with tissue material from affected juveniles (60 d after first feeding). Extensive cytopathic effects (CPE) developed approximately 5 d after inoculation, and were also observed after several passages in the same cell line. Cells from infected cultures showed reactivity with an antiserum against sea bass Dicentrarchus labrax nodavirus in an indirect immunofluorescence test. Analysis of infected cells with reverse transcriptase-polymerase chain reaction (RT-PCR) resulted in a product of the predicted size using primers specific for striped jack Pseudocaranx dentex nodavirus. Electron micrographs of infected SSN-1 cells demonstrated virus particles that were approximately less than 30 nm. Challenge of Atlantic halibut larvae (4 d post-hatching) with supernatants from infected SSN-1 cells resulted in development of VER as verified by immunohistochemistry performed on larvae sampled from Day 9 after challenge. The present results show that a nodavirus from Atlantic halibut has been isolated using the SSN-1 cell line and that virus propagated in cell culture retained virulence.