Friday, April 25, 2008

Influenza's 'round-the-world trip begins in Asia, study finds

For scientists, finding the birthplace of influenza has been like playing a long game of hide-and-go-seek. But the search seems to now be over, as a team of international researchers has shed new light on where flu originates.

A study in Science Magazine looked at influenza A H3N2 viruses, finding that since 2002, the viruses have migrated out of what the authors call the "east and southeast Asian circulation network" before making a one-way trip around the world and eventually dying off in South America. The study shows that the strains come from Asia and then arrive in Europe and North America six to nine months later. Researchers collected 13,000 samples of influenza A H3N2 virus across six continents.

So why Asia? The researchers concluded that different regions in eastern and southeastern Asia experience different rainy seasons throughout the year, which is when flu outbreaks crop up.

"There can be cities that are only 700 miles away from each other, such as Bangkok and Kuala Lumpur, which have epidemics six months apart," said Derek Smith of the University of Cambridge, the corresponding author of the study. "There is a lot of variability like this in East and Southeast Asia, so lots of opportunity for an epidemic in one country to seed an epidemic to another nearby country, like a baton passed by runners in a relay race."

Tourists and trade visitors to Asia help spread the flu throughout the world. If the trend continues, eastern and southeastern Asia may become the new focus of surveillance — which could provide improvements to future vaccines and potentially help predict changes in flu viruses.

With hide-and-go-seek now over, what we've learned can help prevent the flu's spread. Anyone for a game of tag, you're it?

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