New Virus May Pose Risk To Wild Salmon

Atlantic salmon (Salmo salar L.) mariculture has been associated with epidemics of infectious diseases that threaten not only local production, but also wild fish coming into close proximity to marine pens and fish escaping from them. Heart and skeletal muscle inflammation (HSMI) is a frequently fatal disease of farmed Atlantic salmon.

First recognised in one farm in Norway in 1999, HSMI was subsequently implicated in outbreaks in 417 farms in Norway and others in the United Kingdom.

HSMI appears five to nine months after fish are transferred from fresh water to ocean pens, is characterised by epi-, endo- and myocarditis, myocardial necrosis, myositis and necrosis of red skeletal muscle, and up to 20 per cent mortality.

Disease can be induced in naive fish by experimental injection with tissue homogenate from HSMI diseased fish or by cohabitation with fish with HSMI.

Although pathology and disease transmission studies indicated an infectious basis, efforts to identify an agent by using culture, subtractive cloning and consensus polymerase chain reaction, were unsuccessful.

In the study, researchers provided evidence that HSMI is associated with infection with piscine reovirus (PRV). PRV is a novel reovirus identified by unbiased high throughput DNA sequencing and a bioinformatics program focused on nucleotide frequency as well as sequence alignment and motif analyses.

Formal implication of PRV in HSMI will require isolation in cell culture and fulfillment of Koch’s postulates, or prevention or modification of disease through use of specific drugs or vaccines.

Nonetheless, data from the study indicates that a causal relationship is plausible. Therefore, measures must be taken to control PRV not only because it threatens domestic salmon production but also due to the potential for transmission to wild salmon populations.