2:00 Dose of Fluology: Where Do New Flu Strains Come From? Thin Air?

 Where Do New Flu Strains Come From?  Thin Air?

Pigs, usually, by way of birds.  This makes sense; I promise.  To catch the whole thing, we need to think first about Influenza virus itself.

Influenza virus encodes genes on several different pieces of RNA,as illustrated here:

   

Influenza "segmented genome": Looks a bit like fusili pasta

One of those segments carries the gene for the green spikes on the surface, and  a different segment carries the gene for the purple "hammers".  Let's call the graan spikes "H" and the purple hammers "N".  Can anyone guess where this is going?  If you are infected with a flu strain with certain versions of H and N (let's call them versions "2" and "3" ), you would have a flu strain called H3N2.  If you were simultaneous infected with another strain, each with version "1", you would have H1N1.  If both viruses infected the same one of your cells, and something in the virus "assembly line" went wrong, it is possible to generate chimeric viruses with mixed-up segments.  We could call those H1N2, or H3N1.  New strains?  Sure.  But these guys aren't quite so dangerous, because all are of "human" origin.

Back to pigs and pandemic, though.  A human flu virus will typically infect only certain hosts, and the same can be said for avian (bird) flu.  Pigs, though...pigs are trouble.  Pigs have their own flu viruses, but can also be infected with human flu strains and bird flu strains.  If a sad, unfortunate pig is coinfected with both a human and a swine flu virus, a chimeric variant can emerge that is not strictly of human origin.  If said chimeric virus infected another pig which was also infected with an avian strain, a three-part chimera can form.  That guy is big trouble.  That virus has no adaptation to humans, and humans have no intrinsic immunity to anything like it.  This one is far more likely to generate a pandemic.

So there you have it.  They don't fall from the sky, but they do come from the farm.  Take home message: keep your livestock away from each other!