Arch. Virology: Genome Sequence Of A Novel Reassortant H3N3 Avian Influenza Virus

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The remarkable ability of influenza viruses to constantly evolve, reassort, and adapt to new host species makes it the most constant pandemic threat facing humanity. 

And while we watch the more exotic wild H5, H7, and H10 avian flu viruses with justified concern, over more than a century, we've only seen human pandemics from H1, H2, and H3 viruses. 

As we've discussed often over the past few years (see Are Influenza Pandemic Viruses Members Of An Exclusive Club?), the progression of human influenza pandemics over the past 130 years has been H2, H3, H1, H2, H3, H1, H1 . . . .

Simply put, novel H1, H2, and H3 flu viruses appear to have fewer barriers to overcome in order to jump to humans - and while they may not prove as virulent as H5 & H7 avian subtypes - that puts them at or near the top of our pandemic threats list. 

In addition to the 2009 H1N1 pandemic, over the past two decades we've seen a number of new H1, H2, and H3 viruses appear in birds, swine, dogs, seals, and even mink. 

While some people have suggested we are overdue for an H2 pandemic (see J.I.D.: Population Serologic Immunity To H2N2 For Pandemic Risk Assessment), H1 and H3 reassortants are still very much in play.

A few recent blogs on H3 viruses in the wild include:

Emerg. Infect. & Microbes: Novel Triple-Reassortant influenza Viruses In Pigs, Guangxi, China

Genome Announce.: Novel Avian H3N2 Virus Isolated From Domestic Ducks - China, 2016

I&ORV: Triple-Reassortant Novel H3 Virus of Human/Swine Origin Established In Danish Pigs

J. Virol: Novel Reassortant Human-like H3N2 & H3N1 Influenza A Viruses In Pigs

Sci Rpts: Receptor Cell Binding Of Seal H3N8

This week, the Archives of Virology has published details of a novel H3N3 avian influenza virus (AIV) which was collected from South Korea in 2016; a reassortment of both domestic and wild AIVs. The HA gene was most closely related to avian H3N8, while the NA gene closely related to those seen in H10 viruses.

Complete genome sequence of a novel reassortant H3N3 avian influenza virus

While there's no evidence that this particular H3N3 virus poses an enhanced risk to humans, it falls into a suspect cohort of viruses, and H3N3 viruses in the past have been found to infect mammals, including pigs and seals.

Characterization of Avian H3N3 and H1N1 Influenza A Viruses Isolated from Pigs in Canada - 2001

The appearance of H3 influenza viruses in seals - 1995

Most of the influenza reassortment that occurs in birds, pigs, seals, and other mammals goes on out of sight, and without our knowledge.  Luckily, most of these genetic field experiments are doomed to fail, as the bulk of these viruses are unable to compete against established strains. 

Every once in awhile, however, this rolling of the genetic dice produces a new, and biologically `fit' virus against which humans have little or no immunity, and another pandemic erupts. 

So we monitor emerging viruses like this one with considerable interest.