Molecular and Antigenic Characterization of Piscine orthoreovirus (PRV) from Rainbow Trout (Oncorhynchus mykiss)
Kannimuthu Dhamotharan 1, Niccolò Vendramin 2, Turhan Markussen 1, Øystein Wessel 1 ID ,
Argelia Cuenca 2, Ingvild B. Nyman 1, Anne Berit Olsen 3, Torstein Tengs 1,
Maria Krudtaa Dahle 4 and Espen Rimstad 1,* ID
1 Department of Food Safety and Infection Biology, Faculty of Veterinary Medicine, Norwegian University of Life Sciences, 0454 Oslo, Norway;
dhamokan@nmbu.no (K.D.);
oystein.wessel@nmbu.no (Ø.W.);
turhan.markussen@nmbu.no (T.M.);
ingvild.nyman@nmbu.no (I.B.N.);
torstein.tengs@nmbu.no (T.T.)
2 National Institute of Aquatic Resources, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark;
niven@vet.dtu.dk (N.V.);
arcun@vet.dtu.dk (A.C.)
3 Norwegian Veterinary Institute, 5003 Bergen, Norway;
anne-berit.olsen@vetinst.no
4 Norwegian Veterinary Institute, 0454 Oslo, Norway;
maria.dahle@vetinst.no
* Correspondence:
espen.rimstad@nmbu.no; Tel.: +47-672-32-227
Received: 7 March 2018; Accepted: 28 March 2018; Published: 2 April 2018
Abstract: Piscine orthoreovirus (PRV-1) causes heart and skeletal muscle inflammation (HSMI) in
farmed Atlantic salmon (Salmo salar). Recently, a novel PRV (formerly PRV-Om, here called PRV-3),
was found in rainbow trout (Oncorhynchus mykiss) with HSMI-like disease. PRV is considered to be
an emerging pathogen in farmed salmonids. In this study, molecular and antigenic characterization
of PRV-3 was performed. Erythrocytes are the main target cells for PRV, and blood samples that
were collected from experimentally challenged fish were used as source of virus. Virus particles
were purified by gradient ultracentrifugation and the complete coding sequences of PRV-3 were
obtained by Illumina sequencing. When compared to PRV-1, the nucleotide identity of the coding
regions was 80.1%, and the amino acid identities of the predicted PRV-3 proteins varied from
96.7% (1) to 79.1% (3). Phylogenetic analysis showed that PRV-3 belongs to a separate cluster.
The region encoding 3 were sequenced from PRV-3 isolates collected from rainbow trout in Europe.
These sequences clustered together, but were distant from PRV-3 that was isolated from rainbow trout
in Norway. Bioinformatic analyses of PRV-3 proteins revealed that predicted secondary structures and
functional domains were conserved between PRV-3 and PRV-1. Rabbit antisera raised against purified
virus or various recombinant virus proteins from PRV-1 all cross-reacted with PRV-3. Our findings
indicate that despite different species preferences of the PRV subtypes, several genetic, antigenic,
and structural properties are conserved between PRV-1 and-3.
First description of clinical presentation of piscine orthoreovirus (PRV) infections in salmonid aquaculture in Chile and identification of a second genotype (Genotype II) of PRV
Marcos G. Godoy1,2,3,4,5, Molly J. T. Kibenge6, Yingwei Wang7, Rudy Suarez1,3, Camila Leiva1,9, Francisco Vallejos8
and Frederick S. B. Kibenge6*
Abstract
Background: Heart and skeletal muscle inflammation (HSMI) is an emerging disease of marine-farmed Atlantic
salmon Salmo salar, first recognized in 1999 in Norway, and recently associated with piscine orthoreovirus (PRV)
infection. To date, HSMI lesions with presence of PRV have only been described in marine-farmed Atlantic salmon
in Norway. A new HSMI-like disease in rainbow trout Oncorhynchus mykiss associated with a PRV-related virus has
also been reported in Norway.
Methods: Sampling of Atlantic salmon and coho salmon was done during potential disease outbreaks, targeting
lethargic/moribund fish. Fish were necropsied and tissues were taken for histopathologic analysis and testing for
PRV by RT-qPCR assay for segment L1 and conventional RT-PCR for PRV segment S1. The PCR products were
sequenced and their relationship to PRV strains in GenBank was determined using phylogenetic analysis and
nucleotide and amino acid homology comparisons.
Results: The Atlantic salmon manifested the classical presentation of HSMI with high PRV virus loads (low Ct values)
as described in Norway. The coho salmon with low Ct values had myocarditis but only in the spongy layer, the
myositis of red muscle in general was mild, and the hepatic necrosis was severe. Upon phylogenetic analysis of PRV
segment S1 sequences, all the Chilean PRV strains from Atlantic salmon grouped as sub-genotype Ib, whereas the
Chilean PRV strains from coho salmon were more diversified, grouping in both sub-genotypes Ia and Ib and others
forming a distinct new phylogenetic cluster, designated Genotype II that included the Norwegian PRV-related virus.
Conclusions: To our knowledge the present work constitutes the first published report of HSMI lesions with
presence of PRV in farmed Atlantic salmon outside of Europe, and the first report of HSMI-like lesions with
presence
of PRV in coho salmon in Chile. The Chilean PRV strains from coho salmon are more genetically diversified than
those from Atlantic salmon, and some form a distinct new phylogenetic cluster, designated Genotype II.
