Bird flu mutated to infect people more easily.

Bird Flu Virus Mutating Into Human-Unfriendly Form

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.

Birds usually have a body temperature of 41 degrees celsius, and humans are 37 degrees celsius usually. The human nose and throat, where flu viruses usually enter, is usually around 33 degrees celsius.
"So usually the bird flu doesn't grow well in the nose or throat of humans," Kawaoka said. This particular mutation allows H5N1 to live well in the cooler temperatures of the human upper respiratory tract.