Prevalence of influenza A virus in live-captured North Atlantic gray seals: a possible wild reservoir

Influenza A virus (IAV) infection appears to be endemic in Northwest Atlantic gray seals, signaling a potential new mammalian reservoir. Scientists think that IAV mass mortalities in global seal populations originate from wild bird reservoirs, but a three-year study of gray seals conducted by Jonathan Runstadler, Massachusetts Institute of Technology, US, and co-workers suggests that gray seals may also circulate enzootic virus. The researchers took samples from 345 gray seal pups and 57 adults in Canada and the US, and found IAV viral RNA in 9% of pups and 5.3% of adults. Around 19% of pups and 50% of adults tested positive for IAV antibodies, suggesting gray seals are repeatedly infected with IAV. However, they show no signs of disease. Worryingly, viruses can use a host reservoir such as this to evolve before spreading to new species.