Hope for eradicating influenza in salmon

Salmon in Norway could be flu-free in coming years. Photo: Forskningsradet.no

While we humans can expect to suffer from various influenza viruses for the foreseeable future, Norwegian salmon could be rid of their type of influenza within a few years

Infectious salmon anaemia (ISA) has plagued Norway’s aquaculture industry for over 20 years. ISA is one of the most costly diseases in the business; it is not uncommon for the virus to wipe out 50 to 80 percent of the salmon when it strikes a production facility.

Caused by an influenza virus similar to the one that attacks humans, the disease has proven difficult to eradicate. Recent years have seen a growing number of ISA outbreaks, a grave concern to anyone making a living from salmon farming. Now, however, there is good reason to be optimistic.

Free of the flu in a few years?

A research group at the Norwegian School of Veterinary Science (NVH) has been searching diligently for the genes that endow salmon with the highest resistance to viral infection.

These researchers have found roughly 100 genes they believe are involved in the immune system. Now they are trying to pinpoint the three or four genes most important for resistance. In collaboration with colleagues in Scotland and France, they are studying the interaction between the genes of both the host and virus when infection occurs.

The project is jointly funded by the Research Council’s National Program for Research in Functional Genomics in Norway (FUGE) and the EU.

Which ones resist best?

The Norwegian research group is conducting trials in which salmon are infected with the ISA virus. Meanwhile, the Scottish group is exposing salmon to the infectious pancreatic necrosis (IPN) virus, a different pathogen but one that also costs the aquaculture industry dearly. Their research colleagues in France have done studies of the ISA virus on rainbow trout. All these activities have a common objective – to find out which salmon genes put up the best fight against viruses.

Researcher Bjørn Høyheim of NVH is heading the collaboration. He also headed the project to establish salmon’s genetic structure, providing the foundation for exploring the relationship between genes and viruses.

“Step by step, we are getting to know the salmon genes quite well. If we discover that there are certain genes that stand out in each of the three projects we are conducting, then we hope to have found the most fundamental genes for resistance.”

Dr. Høyheim believes it will be possible to breed healthy strains of fish that do not contract influenza.

“Once we have identified the genes that provide the highest resistance to infection, we can select them for breeding strategies. In this way we can breed a salmon strain that is resistant to the ISA virus.”

No one knows how long it will take to find these genes. “It may take five years, even 10 years,” says Dr. Høyheim, who adds optimistically that “it could also happen in two or three years.”

Healthy, but still a carrier?

Once these “supergenes” are found, there will still be much work to be done before Norwegian companies can begin using them in selective breeding.

“We don’t know yet whether certain fish can completely rid themselves of the ISA virus, or if they remain carriers,” explains Dr. Høyheim. “If the individual can withstand the virus, yet still carries it, then other salmon will be infected, including wild salmon. So obviously this needs to be very thoroughly investigated before any selective breeding is begun.”

Useful findings for human medicine?

It just so happens that the ISA virus and human flu virus use the same receptor to enter cells. So this research on salmon could also prove valuable for humans, who must continually cope with new flu viruses.

“Even though the immune systems of humans and salmon are very different, we may still find some basic mechanisms useful for studying interactions between human genes and human flu viruses,” concludes Dr. Høyheim, adding cautiously, “but I certainly don’t want to promise too much in this area.”

Source: Research Council of Norway