Bird flu flies back into the news

Millions of ducks are flying south from Siberia this week, and some are carrying a virus that could lead to a resurgence of H5N1 bird flu in poultry ? and people ? across Eurasia.

"We're issuing an alert because we expect in the coming weeks to see the virus pop up in unexpected places across a wide area," says Jan Slingenbergh, head of the UN Food and Agriculture Organization's early warning system for animal diseases.

H5N1 has cost poultry farmers an estimated $20 billion so far. It has also infected 565 people, of whom 331 died. Virologists are trying to discover the mutations that could enable H5N1 to spread between people and go pandemic.

Dominant strain

The FAO is concerned about a strain of H5N1, called 2.3.2.1, which has been circulating for several years but is now emerging as dominant in birds in Asia.

It is no more virulent than previous strains but it is well adapted to many wild migratory species, so the virus has been carried to countries where H5N1 had been eliminated from poultry, including Bulgaria, Romania and Israel.

H5N1 outbreaks in poultry peaked in 2006, with 4000 across Eurasia and Africa. Extensive culling and vaccination quelled the virus, and by 2008 there were just 302 outbreaks. With the spread of 2.3.2.1, outbreaks are back on the rise. Some samples of the strain in China and Vietnam show its continuing evolution.

"The more cases you get in birds, the more it might spill over into humans," says Slingenbergh.

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