Bird flu, swine flu, now seal flu H3N8

US scientists have identified a new strain of influenza in New England harbor seals – H3N8. They say the strain, presumably made the species leap from birds, might now be a reservoir for an emergent human flu virus.

H3N8 is an influenza type A virus (Orthomyxoviridae) endemic in birds, equines and dogs and although highly contagious was not as such considered a risk to people. A flu outbreak in people in 1889 or 1900 was blamed on this strain but evidence suggests that it was due to H2N2. If H3N8 has mutated and evolved from an avian form into one that infects harbor seals (Phoca vitulina), there is a chance that it could now infect people. Indeed, the virus already has the relevant structure to attack a protein in the human respiratory tract.

Experts have for some time recognised that emergent flu viruses need not only come from East Asia, swine flu, H1N1, being a case in point, the pandemic of 2009 emerging from South America. So, the emergence of a putative pandemic strain in the waters off New England, USA, is worrying, but perhaps not surprising.

It is worth noting that a paper in the same group of journals from 1984 reports on the emergence of an avian influenza virus (H4N5) in harbor seals in the early 1980s. There are presumably other instances so this would suggest that transfer to harbor seals from birds is not an uncommon leap.

BBC News – New flu virus found in seals concerns scientists.

Moscona et al, 2012, mBio; DOI: 10.1128/mBio.00166-12

Influenza A viruses are classified into subtypes based on the antibody response to the viral proteins hemagglutinin (HA), neuraminidase (NA). This distinction gives us the different names, e.g. H5N1, H1N1, H3N8 etc. There are 16 H and 9 N subtypes known, but only H 1, 2 and 3, and N 1 and 2 are usually found in people.

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