caused. Tens of millions of birds died of influenza and hundreds of millions were culled to protect humans.

The chapter begins with a reconstruction of the descent of the virus that infected and killed humans in Thailand and Vietnam during the winter of 2003–2004 from the H5N1 virus first known to have infected humans (in Hong Kong in 1997). These findings indicate that domestic ducks in southern China played a central role in the generation and maintenance of H5N1 and that wild birds spread the virus across Asia, to the point where it is now endemic in the region—an ecological niche from which it now presents a long-term pandemic threat to humans.

The chapter continues with descriptions of the approach taken by two countries most severely affected by the H5N1 epidemic: Thailand and Vietnam. Each country’s circumstances and their handling of the epidemic—beyond the use of common, time-tested strategies for detecting and stamping-out of infection—were unique, as illustrated in these contributions. The diversity of these responses, and their resulting outcomes, offer important lessons for the control of future avian flu outbreaks—a key protection against a human pandemic.

K.S. Li,⁴ Y. Guan,^1,5 J. Wang,^1,2 G.J.D. Smith,^1,2 K.M. Xu,^1,2 L. Duan,^1,2 A.P. Rahardjo,⁶ P. Puthavathana,⁷ C. Buranathai,⁸ T.D. Nguyen,⁹ A.T.S. Estoepangestie,³ A. Chaisingh,⁵ P. Auewarakul,⁴ H.T. Long,¹⁰ N.T.H. Hanh,⁷ R.J. Webby,¹¹ L.L.M. Poon,² H. Chen,^1,2 K.F. Shortridge,^1,2 K.Y. Yuen,² R.G. Webster, J.S.M. Peiris^1,2

Reprinted by permission from Nature (Li et al., 2003), Copyright 2003, Macmillan Publishers Ltd.