ScienceDaily (Sep. 21, 2007)
The influenza A virus does not lie dormant during summer but migrates globally and mixes with other viral strains before returning to the Northern Hemisphere as a genetically different virus, according to biologists who say the finding settles a key debate on what the virus does during the summer off season when it is not infecting people.
"Nobody really knows why flu is a winter disease in the temperate regions and more continuous in the tropics," says Edward Holmes, professor of biology at Penn State. "The big question is, 'Why is flu seasonal?'"
Flu infections in the Northern Hemisphere typically follow a familiar pattern. Some time before the start of the winter infection season, the virus evolves, changing enough to evade the previously primed immune system. Then, just before summer, the virus disappears, only to resurface the next fall with a completely different genetic makeup, ready to fool the immune system anew.
But little is known about what happens to the virus between two successive winters, or how and where it is able to sustain itself.
Flu infections in the Northern Hemisphere typically follow a familiar pattern. Some time before the start of the winter infection season, the virus evolves, changing enough to evade the previously primed immune system. Then, just before summer, the virus disappears, only to resurface the next fall with a completely different genetic makeup, ready to fool the immune system anew.
But little is known about what happens to the virus between two successive winters, or how and where it is able to sustain itself.
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