How the influenza virus can drift and shape-shift to keep us on our toes

As you may have read by now, the new swine flu virus, this new strain H1N1 which is threatening to turn into a pandemic according to the WHO (even though there is much confusion about the actual number of infected/dead victims confirmed to have this strain), is actually an interesting genetic mixture, a chimera if you will with a potpourri of genes from different influenza strains: these may be from multiple host taxa — birds (thought to be the original source of all influenza viruses), humans, and, of course, pigs (from North America and Asia!) — or perhaps all from pigs (the picture is still cloudy). In any case, if you are wondering how such reassorted viruses form, the following video paints a cartoon picture to help you understand. The key thing to remember is that viruses, like many other microbes, are rather promiscuous when it comes to swapping bits of DNA - even across "species" - and such lateral transfer can allow new strains to evolve, even drug-resistant ones, much more rapidly. Here's how influenza may be able to shift the shape of its antigens, and potentially jump between host species:

But, that is not the only trick up this virus' sleeve. Ever wonder why, unlike with other vaccinations which are often a once-in-a-lifetime deal, you've got to take that flu shot over every single year? Because, even in the absence of opportunities to hook-up and swap genes with other viruses, i.e., even when a host is infected by just a single strain of the flu, the virus is constantly changing shape. Mutations arise all the time, and those that change the shape of the antigen such that it is no longer recognized by host antibodies will be naturally selected. Antigen shape therefore drifts around constantly, making it a much more fun game for the host immune system - and our vaccines - to keep up with the flu! It's evolution in action, right within our own bodies and those of animals we cohabit with! You didn't think we had quite liberated ourselves from the clutches of evolutionary processes now, did you? As you ponder that, here's another cartoon depicting antigenic drift:

[Hat-tip: GrrlScientist for finding the videos]