A heart and skeletal muscle inflammation (HSMI) was reported to affect farmed salmon In Norway, in 1999. This fatal disease can now be found in 417 fish farms in Norway and in the United Kingdom. It has become a threat for the farmed fish industry, but the even more concerning problem is that the disease can spread to wild fish getting too close to marine enclosures or from fish escaping them.
One of the growing important food sources nowadays is farmed fish. 100 million tons are produced every year and these figures have a growth rate of 8 percent a year. The problem is that epidemics are becoming a threat for this flourishing industry, mostly for the very popular farmed Atlantic salmon. The HSMI destroys heart and muscle tissue and infected fish have a death rate of over 20 percent.
Evidence that this disease might be caused by an unidentified virus has been found by an international team of scientists. Team leader by W. Ian Lipkin, MD, the John Snow Professor of Epidemiology and director of the Center for Infection and Immunity at Columbia University's Mailman School of Public Health has used the latest molecular techniques to identify this unknown virus. Apparently it has similarities with reoviruses (double-stranded RNA viruses that can infect a large amount of vertebrates) already known to science, without being identical with them.
454 high throughput DNA sequencing and bioinformatics were used by the Columbia U team, for the identification of this virus. This included a new tool called Frequency Analysis of Sequence Data (FASD), invented by Columbia's Department of Biomedical Informatics' Raul Rabadan. Afterward, in Norway and the US, investigators searched for viral sequences in samples from the hearts and kidneys of 29 salmons with three different HSMI manifestations and from 10 healthy fish. The results were positive: 28 of the 29 infected salmons were infected and all of the 10 specimens were in good health.
Gustavo Palacios, the first author of the study and an assistant professor of Epidemiology in the Center, confirmed that HSMI is associated with infection coming from a new sort of reovirus. And even if there is no proof that this virus could spread to humans, it remains a big threat for fish farming and there is a risk of spreading to wild salmons, adds Dr Lipkin.
Future research will be made to confirm that this new reovirus is actually the cause of HSMI, but until then, Norwegian scientists have already begun research for a new vaccine that will protect the farmed Atlantic salmon.