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Bird Flu Genes Decoded; New Clue to How It Kills

Brian Handwerk
for National Geographic News
January 26, 2006
 
A bird-flu pandemic is unlikely until the virus becomes able to be passed from human to human, rather than from animal to human.

To decipher how that might happen, and why the influenza is so deadly in the first place, scientists have to understand how the virus is built. For this, they need lots of genetic data on the virus—and they just got a lot more.

Thanks to a new study, the available genetic information on bird flu has just doubled.

Scientists have created the first large-scale genomic analysis of the avian flu virus. In the process, they have spotted a new variation that could help reveal why some outbreaks—like the present H5N1 virus—are more deadly than others. (Watch video: The Next Killer Flu.)

"[We used] a collection of viruses that spans 30-plus years and was found on all of the major continents," said study co-author John Obenauer, a genetics analyst John Obenauer at St. Jude Children's Research Hospital in Memphis, Tennessee.

"It's a very broad survey of the bird-flu population that includes H5N1 but also all 25 of the known serotypes."

Serotypes are closely related microscopic life-forms.

The study, published in this week's issue of the journal Science, identified 2,196 new bird-flu genes and 169 new complete genomes.

The new abundance of genetic information will be available to other flu investigators worldwide.

"Very little is known about the diversity of the avian flu virus in nature," said Adolfo Garcia-Sastre, a microbiologist at New York's Mount Sinai School of Medicine.

"Obviously birds are the reservoir [for the virus], so without understanding the diversity in that reservoir, we can't understand the source of the viruses that can create pandemics," said Garcia-Sastre, who was not involved in the study.

"These efforts can be combined with efforts to sequence human [influenza] strains and other animal strains, so that we can learn what makes a virus a bird virus, or a human virus, or some other type of virus."

New Road Map to Lethality?

The study not only doubles the amount of available genetic bird-flu data, but it greatly boosts the number of full-genome bird-flu genetic sequences—something that has been sorely lacking.

Sequences are strings of letters that represent the structure of a DNA molecule or strand. The more scientists know about the structure of the virus's DNA, the better they will be able to fight the virus.

Fully sequenced genomes represent life-forms' entire genetic material, rather than just fragments. As such, the full sequences allow scientists to study how individual genes interact with each other.

"Individual genes don't give us the big picture," said Clayton Naeve, a genetics analyst at St. Jude and the new study's senior author.

"Basically, by looking at them in this level of detail, we're learning about their life cycle, what makes them tick, and which genes are important for which functions, Naeve said.

"That's the ultimate goal, and we're getting a better idea of how these viruses evolve."

The new genomes could help scientists learn which genes make a virus especially lethal, or which might give a bird virus the ability to move into humans.

Intriguing Possibilities

The data have already suggested some intriguing possibilities.

"We've observed that avian viruses have a molecular characteristic that human viruses do not," Naeve said.

"That allows them to interact with human cells and potentially shut down pathways in human cells. That finding gives us a whole new means by which viruses interact with cells that we didn't understand before," he said.

"We believe this may be important in [determining] virulence—in combination with other genes."

Experts continue to warn that a global pandemic could be imminent if the H5N1 virus, or another bird-flu strain, genetically mutates into a form that can be easily transferred from person to person.

Such an outbreak could rival the notorious 1918 "Spanish flu" that may have killed as many as 50 million people around the globe.

The UN's World Health Organization estimates that H5N1 has infected some 151 people to date, killing at least 82 worldwide since the first bird-human transmission in 2003.

In recent weeks the virus has spread westward from its East Asian source, killing three Turkish children who contracted the disease from infected poultry.

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