The so-called "bird flu" outbreak in Hong Kong was spread directly from chickens to humans, researchers say.

Scientists had previously said the transmission of viruses from birds to humans was impossible.

But the virtually identical nature of the two viruses has led them to chance their minds.

Writing in The Lancet medical journal, Eric Claas of the World Health Organisation National Influenza Centre, said the finding would raise concerns about a flu pandemic. Millions of people have died this century from flu.

Hong Kong's chickens were slaughtered last year

"This event illustrates the importance of intensive global influenza surveillance," he said.

Mr Claas also ruled out the possibility of a carrier species passing the virus from chickens to humans.

"If you look at the similarities of the two viruses it is very unlikely that there has been another species that could have acted as a mixing vessel," he said.

The team of international virologists based at the WHO centre in Erasmus University, Rotterdam, compared the H5N1 virus, taken from the body of boy who died in the May outbreak of "bird flu" in Hong Kong, with the virus in a chicken.

"Virus cannot spread among humans"

What prevented the "bird flu" virus from escalating to the scale of a pandemic was its inability to spread between humans.

No new cases of the virus have been reported in Hong Kong since the cull of all the former colony's chickens at the end of 1997.

In all, 17 people contracted the disease and five have died.

Mr Claas said: "The good thing about the virus is that it did not have the ability to spread from man to man. However, the potential danger, which is still present, is that it is very likely that the virus will still surface somewhere.

"We're not sure whether it's going to happen now or in 10 years, but it is going to happen."

Robert Belshe, of Saint Louis University Health Sciences Centre in the US, said in The Lancet's editorial that the research provided a stark warning to the governments of the world.

"We need better vaccines. Recombinant protein vaccines and live attenuated vaccines each have their place in the control of influenza. These vaccines need to be studied and their manufacture regulated."
 

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