Remember the H1N1 flu that spread across the planet in 2009? It was the same flu strain that was predominant during this winter's flu season. Now it's turned up in sea otters living off the coast of Washington state, and researchers don't know how it got there.

During the summer of 2011, scientists from the US Geological Survey and the Centers for Disease Control collected blood serum samples from thirty free-ranging sea otters off the Washington coast and found that they were infected with the pandemic 2009 H1N1 virus. More specifically, they found antibodies for the virus in the blood samples of 70% of the otters they assessed. While they weren't sick at the time of capture, the antibodies meant that they had been infected in the past.

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The researchers compared their data to similar measurements taken in 2001-2001, when no signs of influenza were identified in the otters, further supporting the notion that the H1N1 infection was recent. It's the first discovery that sea otters can be infected with influenza viruses.

"We are unsure how these animals became infected," Zhunan Li, a CDC scientist and lead author, said in a statement. "This population of sea otters lives in a relatively remote environment and rarely comes into contact with humans."

One possibility is that they caught it from northern elephant seals. A 2010 study conducted by other researchers found that the central California seals, too, had been infected with by 2009 H1N1 virus. "Elephant seals' summer feeding ranges and breeding areas along the Northeast Pacific coast overlap with areas where the Washington sea otter population is distributed," the researchers write.

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Together, elephant seals and sea otters are the only marine mammals known to be susceptible to the H1N1 virus in particular, though many animals are known hosts for flu viruses more generally: ducks, chickens, pigs, whales, horses, and more.

It's more evidence that human physicians and veterinarians are running into the same problems, and that medical issues cross species lines. It isn't only the fields of human and animal medicine whose boundaries are blurring, but also medicine, wildlife biology, and conservation. The future of medical research, for infectious diseases in particular, will be increasingly interdisciplinary.

Read the entire paper in the journal Emerging Infectious Diseases: Serologic Evidence of Influenza A(H1N1)pdm09 Virus in Northern Sea Otters

Image: Flickr/Michael L. Baird