Dr. Jeffery Taubenberger on: Flu Clues|
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The one thing we can say is that this is definitively an influenza virus, a type A influenza virus of the subtype H1/N1. Influenza viruses come in three different types, A, B and C, of which type A is the major pathogen for humans. But it also infects multiple other animals, including pigs and birds, chickens/ducks, for example. And the influenza viruses are classified based on the different hemagglutinin and neuraminidase proteins on the surface of the viruses. And there are 14 hemagglutinin type subtypes and 9 neuraminidase subtypes. So this particular virus is so-called H1/N1. That was predicted based on the antibodies that people had in their blood who were alive in 1918 and infected with the virus but survived.
The other thing that we can say, which is very interesting was an observation that was made back in the 1930's using this kind of analysis, which was that swine or pig influenza viruses and human influenza viruses were both discovered in the 1930's. Scientists doing analyses back then of antibodies in the serum of 1918 survivors suggested that the antibodies floating in the bloodstream of 1918 survivors was a better match to the influenza viruses in pigs in the 1930's than it was to the influenza viruses that were in circulation in humans in the 1930's. So that led people to think that this was a so-called swine flu.
Our work also seems to confirm that, that the hemagglutinin sequence looks more like the 1930's swine hemagglutinin sequences than it does the human hemagglutinin sequences of the 30's. So there seems to be evidence that there's some relationship to the classic swine flu.
One thing that is an ultimate goal of the project is to try to figure out how it is that this virus got into humans and started a pandemic. Influenza viruses can infect multiple animals, and it's thought that the natural reservoir for influenza viruses are wild waterfowl, like ducks. And in general, it's not thought that avian influenza viruses like those that infect ducks can directly infect humans. In general, it's thought that influenza viruses have to be adapted to life in mammals before they can infect humans, that the viruses have to mutate so that they change the way in which they bind to cells and replicate so that they can successfully grow in human cells, and that pigs may serve as an intermediary, as a mixing vessel between avian-like viruses and human-like viruses.
One thing that this 1918 virus suggests is that all the gene segments we've looked at so far look like they fall into the mammalian class of viruses, that swine/human class, not the avian class. So our analysis suggests that the virus did not come directly from birds to humans in 1918, but went through some kind of mammalian intermediary and pigs are a possibility. Although it's really rather curious as to actually whether pigs infected humans with the 1918 virus or humans infected pigs in 1918. It was clear that there were outbreaks in both humans and pigs almost simultaneously. So it will be really interesting to try to unravel that, as to how the virus actually got into humans.
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