Abstract
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.
Highlights
Transmission of influenza A viruses among species is thought to be an important factor in the evolution and ecology of these viruses
Free-ranging juvenile Northern elephant seals (n = 8) were sampled upon tag deployment at Ano Nuevo State Reserve from 22 to 28 March 2010; and adult females sampled upon return from sea (n = 33) at Ano Nuevo State Reserve and Pt
In 2010 all free-ranging animals tested negative for the matrix gene by room temperature (RT)-polymerase chain reaction (PCR) (n = 17) until 30 April when the first adult female (M778) tested positive upon return to Piedras Blancas (Figure 1)
Summary
Transmission of influenza A viruses among species is thought to be an important factor in the evolution and ecology of these viruses. To date there has been evidence for interspecies transmission between birds and marine mammals and seals and humans [1,2,3] as avian origin isolates (H4N5, H3N8) have been detected in harbor seals (Phoca vitulina) dying with pneumonia; and transmission to humans (H7N7) has been documented following exposure to infected seals that died with disease. These data suggest that seals can both become infected and transmit influenza viruses to conspecifics and other species. Antibodies against influenza virus strains (H3N2) that circulated worldwide in humans have been detected in seals [13,14], indicating that exposure to these human-adapted viruses may be sporadic and infection self-limiting in marine mammals
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