Bird flu still serious threat, scientists say

Like the rumble of distant thunder, bird flu continues to spread across Asia, Africa and Europe. Although it's been out of the news lately in the United States, scientists say that avian influenza, as it's also known, remains a serious threat to human and animal health.

The lethal H5N1 version of the virus is mutating rapidly and rampaging through bird flocks throughout those parts of the world, infecting and often killing people who come in contact with them.

The fear is that the virus will change into a form that makes human-to-human transmission quick and easy. At least seven slightly different subtypes already have been identified.

"New genes are being formed all the time," said Henry Niman, a molecular geneticist who tracks bird flu outbreaks around the world.

Although H5N1 hasn't reached the Western Hemisphere, Joseph Domenech, the chief veterinary officer for the United Nations Food and Agriculture Organization, warned last month that it "could still trigger a human influenza pandemic." A pandemic is a worldwide outbreak such as the 1918 Spanish flu, which killed tens of millions of people in the United States and Europe.