Bird flu could adapt to people

Published 9:00 pm Monday, June 28, 2004

WASHINGTON – A strain of bird flu that scientists fear could lead to a worldwide pandemic in humans is becoming more infectious to mammals.

Millions of chickens and other fowl have had to be slaughtered in Asia – and thousands more have been killed in the United States and elsewhere – to stem outbreaks of avian flu in recent years. Scientists say it is only a matter of time before the virus adapts to spread among humans.

The flu already passed from birds to humans in Hong Kong in 1997, killing six of 18 infected people. Since then human cases also have been reported in Vietnam and Thailand.

Now China-based researchers studying the H5N1 flu strain report that over the years it is changing to become more dangerous to mammals. Their research, based on tests in mice, is reported in Monday’s issue of Proceedings of the National Academy of Sciences.

“Our results demonstrate that while circulating in domestic ducks, H5N1 viruses gradually acquired the characteristics that make them lethal in mice,” reported the team led by Hualan Chen of the Animal Influenza Laboratory of the Chinese Ministry of Agriculture.

While human infections from bird flu remain rare, the World Health Organization considers it a potential major threat to people.

There are two possibilities for the bird virus becoming a serious danger to people.

Viruses constantly mutate and this one could accumulate enough genetic changes to become good at passing between humans. So far the human cases have derived from birds and there is no evidence of the bird flu being passed from person to person.

More scary, the experts say, would be a sudden change caused by combining with a human flu in someone’s body. The two viruses could swap genes and create a potent hybrid with the deadliness of the bird strain and the contagiousness of a regular human strain.

Klaus Stohr, head of the WHO global influenza program, noted that the new study confirms that the virus is evolving fairly rapidly, and viruses that are pathogenic for chickens are more likely to be transmitted to humans because humans are in contact with chickens.

The tests in mice are a type of magnifying glass to help understand how dangerous the virus might be for humans, Stohr said.

While saying there is “no cause for panic,” Stohr observed that the virus’ ability to infect humans raises the possibility of a new worldwide epidemic, or pandemic, of dangerous flu.