Asia is world's cradle for new strains of flu

http://news.yahoo.com/s/ap/20080416/ap_on_he_me/migrating_flu

Asia is world's cradle for new strains of flu

By LAURAN NEERGAARD, AP Medical Writer
1 minute ago

WASHINGTON - Scientists have pinpointed the cradle-to-grave path that
flu takes as it sweeps the globe every year — starting with the birth
of new strains in Asia and ending when the virus burns out in South
America.

In between, influenza catches a ride to North America and Europe about
six to nine months after a new strain emerges in Asia, a pattern that
promises to help health authorities better prepare each winter's flu
vaccine.

Already, monitoring is being beefed up in parts of East and Southeast
Asia "as fast as we can" in hopes of more accurately spotting strains
poised to jump continents, said Dr. Michael Shaw, a flu specialist
with the U.S. Centers for Disease Control and Prevention.

Now, "we know the part of the world to look in, and the probable time
of the year to look," he said.

The good news: Once they leave Asia, new flu strains don't seem to get
more dangerous as they migrate from continent to continent, an
international research team reports in Friday's edition of the journal
Science.

"Once the viruses leave that region, they're really on a pathway to an
evolutionary graveyard," Derek Smith of Britain's University of
Cambridge, who helped lead the team, said in an interview.

Influenza evolves so quickly that slightly different strains circulate
each year. Specialists have long suspected that China was the world's
main incubator, and used outbreaks in Asia to guide the following
year's vaccine recipe.

But the new work shows flu's annual evolution is far trickier than
previously thought.

Every year, a World Health Organization network painstakingly collects
nose or throat swabs of flu patients in over 80 countries, to identify
circulating strains. The researchers studied 13,000 samples of the
most common type of flu — the H3N2 version of Type A influenza —
collected since 2002. They tracked changes in a protein on the virus'
coat, called hemagglutinin, that are small but enough to let flu evade
the immune system and sicken people — in other words, new strains.

The first surprise: Flu may be a winter problem in much of the world,
but H3N2 virus is constantly circulating somewhere in East and
Southeast Asia.
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