DNA vaccine expressing the non-structural proteins of Piscine orthoreovirus delay the kinetics of PRV infection and induces moderate protection against heart -and skeletal muscle inflammation in Atlantic salmon (Salmo salar)

Hanne M Haatveit,Kjartan Hodneland,Stine Braaen,Elisabeth F Hansen,Ingvild B Nyman,Maria K Dahle,Petter Frost,Espen Rimstad

doi:10.1016/j.vaccine.2018.10.094

Abstract

Piscine orthoreovirus (PRV) causes heart- and skeletal muscle inflammation (HSMI) in farmed Atlantic salmon (Salmo salar). Erythrocytes are the main target cells for PRV. HSMI causes significant economic losses to the salmon aquaculture industry, and there is currently no vaccine available. PRV replicates and assembles within cytoplasmic structures called viral factories, mainly organized by the non-structural viral protein µNS. In two experimental vaccination trials in Atlantic salmon, using DNA vaccines expressing different combinations of PRV proteins, we found that expression of the non-structural proteins µNS combined with the cell attachment protein σ1 was associated with an increasing trend in lymphocyte marker gene expression in spleen, and induced moderate protective effect against HSMI.

Highlights

Heart and skeletal muscle inflammation (HSMI) in Atlantic salmon (Salmo salar) is caused by Piscine orthoreovirus (PRV) [1]
We studied whether expression of the PRV
The full-length open reading frames (ORFs) of PRV genes encoding k1, k2, k3, m1, m2, mNS, r1, r2, r3 and rNS, were amplified by the use of PfuUltra II Fusion HS DNA polymerase (Agilent, Santa Clara, CA, USA) from cDNA prepared in an earlier study [27]. pSAV replicon vectors [22] expressing each of these ORFs individually, and the eukaryotic expression vector pcDNA3.1 (+) (Invitrogen) expressing PRV mNS, rNS, r1, r3 or enhanced Green fluorescent protein (EGFP), were constructed

Summary

Introduction

Heart and skeletal muscle inflammation (HSMI) in Atlantic salmon (Salmo salar) is caused by Piscine orthoreovirus (PRV) [1]. HSMI is a prevalent viral disease in salmon aquaculture, and reported in Norway, Scotland, Chile and Canada [2,3,4], mainly in the seawater grow-out phase. The histopathological characteristics of HSMI are epi-, endo- and myocarditis, myocardial necrosis, myositis and necrosis of the red skeletal muscle. HSMI leads to significant economic losses in Atlantic salmon aquaculture. Intervention by optimized management remains a challenge, as PRV is considered ubiquitous in the marine phase of Atlantic salmon farming [7]. A virus closely related to PRV, named PRV-2, was demonstrated to be the etiological agent of erythrocytic inclusion body syndrome in Coho salmon (Onchorhynchus kisutchi) [8].

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Conclusion