Tiny change in flu virus can switch it from merely sickening to deadly

WASHINGTON (AP) -- A tiny change in a virus that causes flu can turn it from an unpleasant annoyance to a killer, a team of researchers has found.

A change in just one of the virus' 10 genes switched a form of flu in chickens to a strain deadly to humans four years ago in Hong Kong, they discovered.

Authorities were forced to kill more than a million chickens in that city to block spread of the flu, which killed six of the 18 humans that it infected.

"What this tells you is that the avian influenza virus can become the virus that causes the disease in humans at any moment," said Yoshihiro Kawaoka, one of the research team at the University of Wisconsin-Madison.

The findings are published in Friday's issue of the journal Science.

"We have found that a limited number of very tiny genetic changes in a specific gene, one called PB2, can have a big effect on how potent the influenza virus is," said Kawaoka.

"Because the influenza virus constantly mutates, and because only a few changes can make a nonpathogenic virus highly pathogenic, we should assume that an outbreak of any new strain or subtype is potentially dangerous to humans," he said.

Robert Lamb, professor of biochemistry at Northwestern University, called the report intriguing.

"In many ways it tells us just how complicated understanding the influenza virus is, that a point mutation in one gene can confer virulence," he said.

The disease reappeared in Hong King this summer and more than a million chickens again were slaughtered.

It has long been known that animals such as swine can harbor viruses, with major epidemics occurring when it jumps from the usual host to humans. The Hong Kong case was the first documented instance of a flu virus jumping directly from chickens to humans, according to the National Institutes of Health.