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HAVBRUK2-Stort program for havbruksforskning

Immune responses and survival in Salmon Gill Pox virus disease: IMMUNOPOX

Alternative title: Immunresponser mot laksepoxvirus og mekanismer for overlevelse ved sykdom: IMMUNOPOX

Awarded: NOK 9.0 mill.

Project Manager:

Project Number:

303415

Application Type:

Project Period:

2020 - 2025

Location:

A serious gill disease in Atlantic salmon was discovered in the early 1990 ies in a Norwegian smolt producing farm. It was suspected to be caused by a virus and this was confirmed many years later, in 2015, when the virus genome was sequenced and diagnostic methods established. The poxvirus causing disease in salmon is called SGPV and infects, and can destroy the gill surface and render the fish unable to breath. In some farms the disease and mortalities can be extreme and up to 70% mortalities is reported. In other cases, there is just infection without any disease. This project, IMMUNOPOX will investigate how the fish combat or fail to combat pox. The project will study host immunity, viral infection and signs of disease and relate this to the disparate outcomes of mortality versus good health. Overall IMMUNOPOX will contribute with basic knowledge of how salmon can fight poxvirus and may also shed some light on the immunesystem of salmon that will be an important steppingstone to make efficient vaccines. In the long term, IMMUNOPOX will ultimately contribute to a fundament for making good decisions regarding health management to reduce losses related to the emerging SGPVD. The Immunopox project was supposed to start in April 2020, but we got some delay with the lab work because of the lockdown during COVID-19 pandemic. VI has moved to Ås and need to fully establish in the new facilities. The pox challenge trials which aim to obtain salmon fish that survives an SGPV in vitro infection are kept on hold for now, and we are waiting for the wet lab facitlity at Ås, to be ready. We have made the plasmids (system that can carry genes) with the sequences of three poxvirus-surface proteins. We have taken our first steps in establishing insect cell culture. Further, we are working on the characterization of the purified rabbit serum using immunostaining and western blot, before the further purification of the native poxvirus L1 protein. We did a pilot study to investigate the expression of secretory immunoglobulins (IgM and IgT) in fish samples collected in previous challenge trials and wait for more samples from late time points after infection. We have established the duplex RNAscope on salmon gills to study T cell response and the results are now published in Frontiers in immunology and is entitled «Mucosal and Systemic Immune Responses to Salmon Gill Poxvirus Infection in Atlantic Salmon Are Modulated Upon Hydrocortisone Injection». Here, we analysed a set of ten SGPV genes predicted as expressed early, intermediate and late were studied during the course of SGPV infection in gills. The three members of the B22R gene family were the only genes found to be expressed early in the samples available. RNAscope was used to compare detection of SGPV B22R1 and D13L transcripts in gills from Atlantic salmon at 1 and 3 days after exposure to SGPV revealing significant differences in detection of SGPV-positive cells at day 1. To get more insight into the pathology and especially circulatory changes during SGPV outbreaks, serial sections stained using stainigmethods such as Martius, Scarlet and Blue to study presence and distribution of fibrin. These sections are being assessed

In the 2015 The Norwegian Veterinary Institute (NVI) and National Institute of Health (NIH), USA published the Salmon Gill Pox Virus (SGPV) genome and the associated gill disease in Atlantic salmon. Recent studies show that SPGV disease has a wide distribution, is a significant welfare problem and has a huge negative economical impact. The ongoing NRC fincanced project SALPOX ongoing at NVI has resulted in a successful experimental model recreating the enigmatic paradox of healthy recovery versus the acute lethal pox syndrome affecting both gill and the general circulation. This opens for studies as it was previously impossible to generate knowledge of the determinants of survival versus acute death. IMMUNOPOX will over the time course of repeated experimental challenges characterize host immunity, viral infection and pathology with regard to their nature, levels and localization and relate to the disparate outcomes of mortality versus good health. Norwegian University of Life Sciences will contribute with studies of the role of the newly discovered gill mucosal associated immune tissues. This will extend the existing knowledge of SGPVD pathology and test the hypothesis that survivors of SGPVD become immune to SGPVD upon rechallenge. Finally, integration of the data into suggested immuno- and patho-genesis respectively will be made as a foundation for future research to shift the balance towards a healthy outcome. Overall IMMUNOPOX will contribute with basic knowledge of host immune responses during SGPVD, that may also shed new light on the salmon immune system, that will be an important steppingstone to make efficient vaccines. In the long term,IMMUNOPOX will ultimately contribute to a fundament for making good decisions regarding health management to reduce losses related to the emerging SGPVD.

Funding scheme:

HAVBRUK2-Stort program for havbruksforskning