Bird flu virus mutating into human-unfriendly form

By Maggie Fox, Health and Science Editor

NEW YORK (Reuters) - The H5N1 bird flu virus has mutated to infect people more easily, although it still has not transformed into a pandemic strain, researchers said on Thursday.

The changes are worrying, said Dr. Yoshihiro Kawaoka of the University of Wisconsin-Madison.

"We have identified a specific change that could make bird flu grow in the upper respiratory tract of humans," said Kawaoka, who led the study.

"The viruses that are circulating in Africa and Europe are the ones closest to becoming a human virus," Kawaoka said.

Recent samples of virus taken from birds in Africa and Europe all carry the mutation, Kawaoka and colleagues report in the Public Library of Science journal PLoS Pathogens.

"I don't like to scare the public, because they cannot do very much. But at the same time it is important to the scientific community to understand what is happening," Kawaoka said in a telephone interview.

The H5N1 avian flu virus, which mostly infects birds, has since 2003 infected 329 people in 12 countries, killing 201 of them. It very rarely passes from one person to another, but if it acquires the ability to do so easily, it likely will cause a global epidemic.

All flu viruses evolve constantly and scientists have some ideas about what mutations are needed to change a virus from one that infects birds easily to one more comfortable in humans.