Tracking influenza's every movement( Its the case of the missing flu viru...)

Its the case of the missing flu virus. When the flu isnt making people sick, it seems to just vanish. Yet, every year, everywhere on Earth, it reappears in the appropriate season and starts its attack. So where does it go when it disappears? Does it hibernate, lying dormant in a few people and preparing for its next onslaught? Does it bounce around from the Northern hemisphere to the Southern hemisphere and back, following the seasons?

Neither, it turns out. The viruss breeding grounds are in Asia, a crew of virus-hunters has found, and it then teems out to take over the world anew each year. New varieties almost always evolve in Asia and then hitch a ride with travelers, spreading to Europe, Australia and North America and finally to South America, where they die away.

The work may make the flu vaccine even better than it already is. Because the flu virus is constantly evolving, scientists meet at the World Health Organization twice a year to decide whether to update the vaccine. Their job is made harder because they have to decide on a formulation a year in advance of when the flu will actually hit, to allow time for the vaccine to be manufactured and administered. So they have to predict which of the strains of flu virus are going to be causing the most disease a year down the line.

In order to try to predict how flu viruses might evolve, we have to understand how theyre moving around the world and where theyre evolving, says Derek Smith, now of the University of Cambridge and formerly of the Santa Fe Institute, corresponding author of the research. Asia, the study suggests, is the best place to look for up-and-coming strains.

The team published its findings April 18 in Science (http://www.sciencemag.org/cgi/content/full/320/5874/340).

The team traced the viruss steps by studying 13,000 flu samples from around the world. The World Health Orga
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