Sea otters have joined the ranks of ducks, chickens, pigs, whales, horses and elephant seals—all animals that can contract influenza. According to a new study by the U.S. Geological Survey, sea otters living in a remote area in Washington state were carriers of the H1N1 virus, the strain of human flu that caused a pandemic back in 2009. This is only the second case of scientists discovering a marine mammal species that can contract the human flu, the researchers point out.

The USGS scientists have no idea how the otters contracted the flu. Few people journey to the otters' neck of the Washington coast. "Potential contact between northern elephant seals and sea otters is one possibility; 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 in the paper.

Regardless of how the otters came into contact with the virus, it appears that they are indeed quite susceptible to it. In a survey of 30 otters conducted in 2009, 70 percent came back positive for the human H1N1 virus antibodies. None of the otters, the researchers report, were visibly ill, however.

“Our new study identifies sea otters as another marine mammal species that is susceptible to influenza viruses and highlights the complex interspecies transmission of flu viruses in the marine environment,” the researchers commented in a statement. Now that they've identified otters as a potential virus reservoir, they plan to try to determine its origin and figure out how it affects both otters and the environment they live in.