Isolation and characterization of the fall Chinook aquareovirus

Salmon are paramount to the economy, ecology, and history of the Pacific Northwest. Viruses constitute one of the major threats to salmon health and well-being, with more than twenty known virus species that infect salmon. Here, we describe the isolation and characterization of the fall Chinook aquareovirus, a divergent member of the species Aquareovirus B within the family Reoviridae.

The virus was first found in 2014 as part of a routine adult broodstock screening program in which kidney and spleen tissue samples from healthy-appearing, adult fall Chinook salmon (Oncorhynchus tshawytscha) returning to a hatchery in Washington State produced cytopathic effects when inoculated onto a Chinook salmon embryo cell line (CHSE-214). The virus was not able to be confirmed by an RT-PCR assay using existing aquareovirus pan-species primers, and instead was identified by metagenomic next-generation sequencing. Metagenomic next-generation sequencing was used to recover the full genome and completed using 3' RACE.

The genome of the fall Chinook aquareovirus contains 11 segments of double-stranded RNA totaling 23.3 kb, with each segment flanked by the canonical sequence termini found in the aquareoviruses. Sequence comparisons and a phylogenetic analysis revealed a nucleotide identity of 63.2% in the VP7 gene with the Green River Chinook virus, placing the new isolate in the species Aquareovirus B. A qRT-PCR assay was developed targeting the VP2, which showed rapid growth of the isolate during the initial 5 days in culture using CHSE-214 cells.

This sequence represents the first complete genome of an Aquareovirus B species. Future studies will be required to understand the potential pathogenicity and epidemiology of the fall Chinook aquareovirus.