A team of researchers reporting in the journal PLoS ONE has detected the influenza H1N1 virus in Northern Elephant Seals (Mirounga angustirostris) off the central California coast.

Prof Tracey Goldstein from the University of California Davis’ One Health Institute and Wildlife Health Center, lead author of the study, said: “we thought we might find influenza viruses, which have been found before in marine mammals, but we did not expect to find pandemic H1N1. This shows influenza viruses can move among species.”

Between 2009 and 2011, the team tested nasal swabs from more than 900 marine mammals from 10 different species off the Pacific Coast from Alaska to California. They detected H1N1 infection in two northern elephant seals and antibodies to the virus in an additional 28 elephant seals, indicating more widespread exposure. Neither infected seal appeared to be ill, indicating marine mammals may be infected without showing clinical signs of illness.

“The findings are particularly pertinent to people who handle marine mammals, such as veterinarians and animal rescue and rehabilitation workers,” Prof Goldstein said. “They are also a reminder of the importance of wearing personal protective gear when working around marine mammals, both to prevent workers’ exposure to diseases, as well as to prevent the transmission of human diseases to animals.”

H1N1 originated in pigs. It emerged in humans in 2009, spreading worldwide as a pandemic. The World Health Organization now considers the H1N1 strain from 2009 to be under control, taking on the behavior of a seasonal virus.

“H1N1 was circulating in humans in 2009. The seals on land in early 2010 tested negative before they went to sea, but when they returned from sea in spring 2010, they tested positive. So the question is where did it come from?” Prof Goldstein said.

“When elephant seals are at sea, they spend most of their time foraging in the northeast Pacific Ocean off the continental shelf, which makes direct contact with humans unlikely.”

The seals had been satellite tagged and tracked, so the researchers knew exactly where they had been and when they arrived on the coast.

The first seal traveled from California on Feb. 11, 2010 to southeast Alaska to forage off the continental shelf, returning to Point Piedras Blancas near San Simeon, California, on April 24. The second seal left Ano Nuevo State Reserve in San Mateo County, Calif., on Feb. 8, 2010 traveling to the northeast Pacific and returning on May 5.

Infections in both seals were detected within days of their return to land.

“Exposure likely occurred in the seals before they reached land, either while at sea or upon entering the near-shore environment.”

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Bibliographic information: Goldstein T et al. 2013. Pandemic H1N1 Influenza Isolated from Free-Ranging Northern Elephant Seals in 2010 off the Central California Coast. PLoS ONE 8 (5): e62259; doi: 10.1371/journal.pone.0062259