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Scientists have 'resurrected' an extinct virus that, back in 1918, killed 20-50 million people in the world's largest flu pandemic.

They say their research on the 'Spanish flu' virus shows that the bird flu virus now spreading in Asia (H5N1) could become highly infectious to people without having to combine first with a human virus.

Jeffery Taubenberger, of the US Armed Forces Institute of Pathology, and colleagues have spent eight years working out the 1918 virus's genetic code. To do this, they used fragments of virus genetic material taken from lung samples of people who died in the 1918 pandemic.

The researchers say the virus was originally a bird flu virus and is genetically similar to H5N1.

Experts fear that the H5N1 virus could combine with a human flu virus to create an extremely infectious and lethal 'pandemic' virus that could kill millions.

But the final stages of Taubenberger's study, published tomorrow (6 October) in Nature, suggests that this was not necessary for the 1918 virus, which instead gradually evolved an ability to infect people without ever coming into contact with a human virus.

He warns that the similarities between the two viruses mean H5N1 could also evolve on its own, given time.

Taubenberger was also part of a second team that took the virus's genetic sequence and, using a technique called 'reverse genetics', recreated a live version of the 1918 virus.

By infecting mice, chicken embryos, and human lung cells with the recreated virus, the researchers found that it was more infectious than any other human flu virus.

They publish their findings on Friday (7 October) in Science

Taubenberger says studying the 1918 virus should provide a "checklist" of genes that H5N1 would have to acquire to become infectious enough to cause a pandemic. This, he says, could help efforts to monitor this threat.

He adds that the reconstructed virus should help reveal the genes that made it, and possibly other human flu viruses, so deadly.

Already, they have been able to pinpoint four of these out of the virus's total of eight.

Link to full paper in Nature  

Link to full paper in Science

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