A Thai farmer wearing protective clothing on his land

Thai farmer Noi Tritanasombat waits for a health worker to test his ducks for the H5N1 virus. Such measures have checked the spread of bird flu in Thailand, but outbreaks elsewhere in Asia pose a continuing threat. The virus could evolve into a form that passes easily from person to person—and could spread around the world by jet.

Photograph by Lynn Johnson

Tracking the Next Killer Flu

ByTim Appenzeller
December 02, 2009

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