“Our findings show that salmon farms are, indeed, a source of infection for wild fish. Viruses leave a genetic fingerprint. The genetic fingerprint shows that the same viruses that are on the farms are in the wild fish. All the evidence suggests that the virus is being transmitted from the farm to wild fish. I haven’t seen any evidence that says that’s not happening,” said Dr Gideon Mordecai, a viral ecologist at the University of British Columbia and the lead author of a paper published in Science Advances last month.