Bird Flu Strain Diversified, May Be Harder to Conquer

Brian Handwerk
for National Geographic News
February 7, 2006

Scientists may need to cast a much wider net to track and curb the spread of bird flu, a new study suggests.

That's because the deadly H5N1 avian influenza strain has several distinct genetic branches, or sublineages, spread across several geographic regions, the research shows.

Robert Webster, a virologist at St. Jude Children's Research Hospital in Memphis, Tennessee, and in the department of microbiology at the University of Hong Kong, co-authored the study.

He says the variations may pose a troubling puzzle for scientists hoping to develop effective, strain-specific human vaccines to battle a possible pandemic.

"The virus in Turkey is different from the one in Indonesia, which is different from the one in Vietnam, and so on," Webster said. "We have no idea which might be the one that takes off—if any of them do."

Webster and colleagues report their findings in this week's edition of the journal Proceedings of the National Academy of Sciences.

Experts warn that if any sublineage of H5N1 mutates into a form that can be easily transferred between people, a global pandemic could be imminent and result in tens of millions of deaths.

The World Health Organization (WHO) estimates that H5N1 has so far infected about 160 people in 7 countries, killing at least 85 worldwide since the first bird-to-human transmission in 2003.

(Read an excerpt from a National Geographic magazine feature about bird flu.)

More Complex Than Thought

While tracking poultry around Southeast Asia, Webster and his team found that different geographical locales feature distinct sublineages of the disease. They have identified at least four branches so far.

"This is the first clear indication that the H5N1 situation is more complicated than we think," said Hon Ip, diagnostic virologist at the U.S. Geological Survey's National Wildlife Health Center in Madison, Wisconsin.

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