Researchers have found swine flu in elephant seals – what does this mean for the seal population?
Northern elephant seals (Mirounga angustirostris) from the central California coast showed evidence of H1N1 influenza A virus infection and exposure in 2010 and 2011. This is the first time we’ve seen pandemic H1N1 in marine mammals, and the first avian influenza infection detected in marine mammals on the West Coast of the United States.
No seals showed clinical signs of disease and virus was isolated in only two cases, however a number of other animals had antibodies to H1N1.
H1N1 Virus Isolated From Two Adult Female Elephant Seals
Between 2009 to 2011, a survey for influenza A virus along the Pacific coast from Alaska to California tested nasal swabs from more than 900 marine mammals of ten different species.
The survey isolated the H1N1 virus from the nasal swabs of two seals in 2010, but didn’t detect the virus in nasal swabs from any of the other species surveyed. The researchers then used serologic testing of samples from free-ranging seals, and pups admitted to rehabilitation, to further evaluate the timing and extent of exposure to H1N1.
Of the free ranging animals tested, 14% had antibodies to H1N1 in their blood. The researchers compared these results with archived serum samples from 238 elephant seal pups admitted for rehabilitation in 2010 and 2011. None of the pups tested positive for antibodies until April of 2010, after which 7% tested seropositive for antibodies to H1N1. In 2011, the number of animals with H1N1 antibodies increased to 19% but their titers were lower, possibly suggesting passive maternal transfer of antibodies in the second year of the virus being present.
Swine Flu Virus Exposure Source
Decoded Science spoke with Dr. Tracey Goldstein, UC Davis Wildlife Health Center faculty member and lead author on the paper. She noted that one of the interesting aspects of this survey was that it is unclear where the seals were first exposed to the virus.
The free ranging female northern elephant seals tested were being satellite tracked as part of the Tagging of Pacific Predators (TOPP) program. It would seem logical that exposure to humans while onshore would be the most likely route of transmission. However, the seals tested positive within a few days of their return from foraging in the northeast Pacific, suggesting they encountered the virus at sea or near shore. Potential sources of exposure may be from seabirds congregating in the same feeding areas or perhaps from human waste discharged from ships passing through their migration route or from near-shore exposure as they returned from their migration.
Influenza Viruses and Human Transmission
There have been disease outbreaks in marine mammals, largely on the East Coast of the United States, linked to various influenza A strains— H7N7 in 1979/1980, H4N5 in 1982/1983 and H3N8 in 2011. In most of these cases, there was active disease present.
This makes public health concerns much more obvious. The average person is less likely to approach a clearly sick animal, thus reducing the risk of direct transmission. A seal that carries the virus, but don’t look sick, is more likely to pass on the disease. We don’t yet know H1N1-positive elephant seals posed a risk to humans.
Dr. Goldstein said that there is the possibility that these animals could be carriers, shedding the virus while not displaying any signs of disease. She suggests that this also serves as a reminder that healthy-appearing wildlife may be carrying diseases that do not pose a risk to their species but could be a concern for human health. If you find a marine mammal on the beach in the US, do not approach the animal – instead, immediately contact the nearest Marine Mammal Stranding Network member organization, who will assess the animal.
Goldstein T, Mena I, Anthony SJ, Medina R, Robinson PW, et al. Pandemic H1N1 Influenza Isolated from Free-Ranging Northern Elephant Seals in 2010 off the Central California Coast. (2013). PLoS ONE 8(5): e62259. doi:10.1371/journal.pone.0062259. Accessed September 10, 2013.
Tagging of Pacific Predators. Predator Tagging Map. (2013). Accessed September 10, 2013.