Avian Flu Hatches Again

Earlier this year, a massive epidemic of avian flu hit eight Asian countries, killed at least 23 people and led to the death or culling of more than 100 million chickens—and that could be just the prelude. Last week China, Thailand and Vietnam all announced that they had chickens infected with the virulent H5N1 virus that causes avian flu, dashing hopes that the bird culls earlier this year had eradicated it. Officials in China appear to have responded quickly, barring the export of poultry from the affected Anhui province and culling 30,000 birds within a three-kilometer radius of the original infection. Thailand and Vietnam, which—like China—were slow to deal with the earlier outbreak, also wasted little time responding to the new cases. So far, officials say there's no evidence that humans have been infected in this latest outbreak.

Two new research studies warn, however, that widespread human infection may be only a matter of time. A report published in Nature last week by scientists at the University of Hong Kong and Shantou University shows that the H5N1 virus has evolved rapidly since it first infected humans in Hong Kong in 1997, killing six. The result was the powerful strain of H5N1 that caused this winter's unusually widespread and lethal outbreak. Another recent study shows that the latest strains of the virus proved the most deadly to lab mice—raising worries that H5N1 is also becoming increasingly dangerous to humans.

The real fear is that H5N1 could crossbreed with a standard human-flu virus to create a highly lethal, highly contagious strain with the potential to cause a global flu pandemic. Professor Yi Guan of the University of Hong Kong, the lead researcher on the Nature paper, worries that H5N1 is evolving so fast that it may gain the ability to infect humans by mutating on its own, without mixing with a human virus, much as SARS did. Yi says the latest outbreaks show that the virus has become endemic to the region, with a difficult-to-eradicate foothold in migratory birds, creating a biological time bomb that could go off without warning. With wide-scale production of an H5N1 human vaccine several months away at the earliest, experts are urging governments to clean up poultry farming and transportation, reassess live-market practices and intensify disease surveillance in birds and humans. "We must face the problem, not avoid it," says Yi—or the problem will face us soon enough.