|Northern Elephant Seals Mirounga angustirostris|
photo: Mike Baird
Interspecies transmission of influenza A is an important factor in the evolution and ecology of influenza viruses. Marine mammals are in contact with a number of influenza reservoirs, including aquatic birds and humans, and this may facilitate transmission among avian and mammalian hosts. Virus isolation, whole genome sequencing, and hemagluttination inhibition assay confirmed that exposure to pandemic H1N1 influenza virus occurred among free-ranging Northern Elephant Seals (Mirounga angustirostris) in 2010. Nasal swabs were collected from 42 adult female seals in April 2010, just after the animals had returned to the central California coast from their short post-breeding migration in the northeast Pacific. Swabs from two seals tested positive by RT-PCR for the matrix gene, and virus was isolated from each by inoculation into embryonic chicken eggs. Whole genome sequencing revealed greater than 99% homology with A/California/04/2009 (H1N1) that emerged in humans from swine in 2009. Analysis of more than 300 serum samples showed that samples collected early in 2010 (n = 100) were negative and by April animals began to test positive for antibodies against the pH1N1 virus (HI titer of ≥1:40), supporting the molecular findings. In vitro characterizations studies revealed that viral replication was indistinguishable from that of reference strains of pH1N1 in canine kidney cells, but replication was inefficient in human epithelial respiratory cells, indicating these isolates may be elephant seal adapted viruses. Thus findings confirmed that exposure to pandemic H1N1 that was circulating in people in 2009 occurred among free-ranging Northern Elephant Seals in 2010 off the central California coast. This is the first report of pH1N1 (A/Elephant seal/California/1/2010) in any marine mammal and provides evidence for cross species transmission of influenza viruses in free-ranging wildlife and movement of influenza viruses between humans and wildlife.
H1N1 Swine Flu Virus Found in Marine Mammals for the First Time
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.
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.”
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: dx.doi.org/10.1371/journal.pone.0062259