Quick Guide: Bird flu
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Global threat

Evolving menace

Virus origins

Human dimension

Fighting the virus

Global threat

Lethal global flu epidemics tend to occur three or four times a century.

Scientists believe a new one may be imminent and is likely to be triggered by bird flu.

The latest H5N1 strain has killed millions of birds and scores of humans since 2003.

Many experts fear the virus will soon mutate into a strain more easily spread among humans.

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