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The American Experience

Dr. Jeffery Taubenberger on: Seeds of a Pandemic
 Dr. Taubenberger of the Armed Forces Inst. pf Patholgy Listen in Real Audio

Influenza viruses are known to continually circulate in humans and they cause small outbreaks every winter. And with great regularity, new influenza viruses arise in human populations that spread throughout the world very quickly and cause a so-called pandemic, which is a major epidemic. These happen about every 10 to 30 years, if you go back at least to the records of the 1700's, and probably have happened throughout human history. What happens here is that a completely new kind of influenza virus emerges.

Influenza viruses are not stable genetically. They're really, in a sense, chameleon viruses. They can change their coats. And this is presumably an adaptation of the virus, to evade the host immune response, so that the influenza virus that was circulating last year is not the same as the influenza virus that's circulating this year. That's why they have to reformulate the vaccine preparations every single year and people have to be reinoculated, because the virus mutates and changes enough so that your prior immunity would not be sufficient to prevent you from being infected with the virus. So they're very clever in that sense.

These mutations tend to be sort of slow and steady and accumulate every year. Occasionally, however, a really dramatic change occurs in which an entirely new kind of influenza virus emerges that hasn't existed before. Usually it's thought that it's a recombinant. That is, it's a mixture of the genes of two different influenza viruses. So that if one animal, say a pig, is infected with a bird influenza virus and a human influenza virus, what could happen is that you could make a mixed virus, a recombinant virus that had some genetic material of the bird virus and some genetic material of the human virus, and it would be so different that no one on earth would have any kind of immunity to it and it would allow it to spread like wildfire through human populations.

So presumably that's what happens in pandemics, and there have been three of them in this century. In 1918, in 1957 and 1968. So it's been 30 years since the last one occurred. So if you want to bet the odds, it's very likely that another pandemic is really due.

I'm rambling here, I'm sorry. So one of the goals of the project with 1918 is to not only think about what might be the genetic basis for a virus that was so virulent, that was really different in its behavior from other known influenza viruses, and also how it could have emerged, so that we can use this information to look for the emergence of new influenza viruses in pigs or in humans that actually may be the source of a new pandemic.



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