Key Viral Change Could Help Bird Flu Spread

(HealthDay News) -- U.S. scientists say they've spotted a crucial step the deadly H5N1 bird flu virus must take in order to spread easily in humans.

Since H5N1 first appeared in 1997, there have been more than 250 human infections. Of those, 150 were fatal. Most of the human infections were the result of close contact with infected birds.

So far, the virus has not developed the ability to spread easily among humans.

Now, researchers led by University of Wisconsin-Madison virologist Yoshihiro Kawaoka have pinpointed a single change in a viral protein that helps H5N1 infect the cells of the upper respiratory system in mammals. The adaptation could enable the virus to infect a wider range of cell types and spread more easily among humans, the scientists said.

Being able to establish itself in the upper respiratory system enables easy transmission of the virus through coughing and sneezing, Kawaoka noted. However, other yet-to-be identified changes would have to occur before the H5N1 virus could potentially trigger a flu pandemic.

The finding appears in the journal PLoS Pathogens.

"The viruses that are in circulation now are much more mammalian-like than the ones circulating in 1997," Kawoka said in a prepared statement. "The viruses that are circulating in Africa and Europe are the ones closest to becoming a human virus."

More information
The U.S. Centers for Disease Control and Prevention has more about bird flu.