Salmon virus potential threat to wild stocks

Farmed Atlantic salmon being pumped into a slaughtering facility near Bergen, Norway. (Photo: Odin Hjellestad)

The often fatal farmed Atlantic salmon (Salmo salar L) disease known as heart and skeletal muscle inflammation (HSMI) may be posing a risk to wild fish coming in close proximity to marine pens and escaped farmed fish.

First detected in salmon on a farm in Norway in 1999, HSMI has now been found in 417 fish farms there as well as in the UK. The disease ravages heart and muscle tissue and kills up to 20 per cent of infected animals.

Attempts to identify the pathogen causing the disease have been fruitless recently. But now cutting-edge molecular techniques have led researchers to new results.

The disease may be caused by a previously unknown virus, according to an international team led by W Ian Lipkin, MD, the John Snow Professor of Epidemiology and director of the Centre for Infection and Immunity at Columbia University’s Mailman School of Public Health. This virus is related to previously known reoviruses, which infect various vertebrates.

These findings are published online in PLoS One.

“Our data provide compelling evidence that HSMI is associated with infection with a new reovirus,” said Gustavo Palacios, first author of the study and assistant professor of Epidemiology in the Centre.

Dr Lipkin added that it poses a threat to aquaculture and has the potential to spread to wild salmon stocks.

To identify the virus, the researchers employed 454 high throughput DNA sequencing and bioinformatics, including the new Frequency Analysis of Sequence Data (FASD) tool, which was pioneered by Raul Rabadan of Columbia’s Department of Biomedical Informatics. Scientists in Norway and the US then sought viral sequences in heart and kidney samples from 29 salmon from three different HSMI outbreaks and 10 from healthy farms.

Results showed that 28 of the 29 (96.5 per cent) known HSMI samples and zero of the 10 healthy salmon samples were positive.

Investigators also tested 66 samples from wild salmon swimming in nine coastal Norwegian rivers. The virus was in this case detected in 16 samples (24.2 per cent), although generally in concentrations lower than found in infected farmed fish.

“The speed of this process, and the enthusiasm on both sides of the Atlantic created a very fruitful collaboration,” stated Espen Rimstad, a professor at the Norwegian School of Veterinary Science in Oslo. “Using the expertise of our colleagues at Columbia in high throughput sequencing and advanced bioinformatics, we had within a few weeks the whole genome sequence of a hitherto unknown virus.”

Further research is necessary to confirm that the reovirus causes HSMI. Meanwhile, scientists in Norway have already begun to create a vaccine for farmed Atlantic salmon.

Constituting an increasingly important source of food and income, global annual consumption of fish is forecasted to climb from 110 million tonnes this year to more than 200 million tonnes in 2030.

Source: FIS

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