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H1N1 Appears To Be Transmittable From Human To Pig
mpetch writes "In an interesting twist, it appears that H1N1 influenza can be transmitted from humans to swine. Apparently a Canadian pig farmer vacationed in Mexico, returned to Canada and infected about 10% of the swine on an Alberta farm. The swine subsequently developed flu symptoms."
Influenza viruses go back and forth between humans, pigs, and birds, and they also mutate regularly. So, this didn't really "start" anywhere, it's a normal part of how the influenza virus lives.
Current reports indicate that this strain of H1N1 influenza contains genetic material from swine, avian, and human forms of the disease. That's probably why it can spread easily from humans to pigs; normally, a virus does not cross species unless there is frequent or prolonged close contact between the two, because making the leap depends on genetic mutation. In this case, the virus is already adapted to both hosts.
To further clarify, the name "H1N1" refers only to a particular configuration of two proteins on the surface of the virus (H is hemagglutinin and N is neuraminidase). The configuration of these proteins determines how the immune system will react to a given strain of influenza (i.e. which antibodies will be able to recognize and attack it), which is the most useful information to have when it comes to treating the disease, but there are other factors that determine a given strain's properties.
So the news here is not that H1N1 flu can jump from humans to pigs -- it can't, not necessarily -- the news is that this variety appears to be able to. And it's not that we didn't know this could be possible -- we've seen this kind of thing countless times, and in fact it's believed that all forms of influenza ultimately come from birds -- it's just that calling it "H1N1 flu" doesn't give us enough information to make those kinds of predictions about its virulence.
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