FEARS that avian flu will trigger a global pandemic that could kill up to 150 million people intensified yesterday after research revealed similarities between the virus and possibly the deadliest germ in history.

Scientists have re-created the “Spanish flu” virus that killed up to 50 million people in 1918-19 and shown that it shared traits with the H5N1 strain of avian flu.

An analysis of the re-created pathogen has shown that, like its modern cousin, it began as a bird virus and jumped species into humans with mutations that made it peculiarly virulent and lethal.

A related study has identified that several of these mutations are also present in the H5N1 strain that has killed at least 60 people in Thailand, Vietnam, Cambodia and Indonesia. This could mean that the contemporary strain is starting along the evolutionary pathway that transformed a bird virus into a human-killer in 1918.

Jeffrey Taubenberger, of the US Armed Forces Institute of Pathology, who contributed to both studies, said: “This suggests that these H5N1 viruses might be acquiring the ability to adapt to humans, increasing their pandemic risk.” Insights from the work promise to assist the development of drugs against highly virulent forms of flu, and could provide a “checklist” of dangerous genetic traits that would improve surveillance of hazardous strains.

The research also indicates that the Spanish flu jumped species directly from birds to humans. The less serious pandemics of 1957 and 1968 began when an avian virus first mingled its genes with those of a flu strain that could already infect people, either in a human or in animals such as pigs that can harbour both varieties.

If a direct jump has occurred once, it could occur again, providing a fresh route by which modern avian flu could evolve. “For H5N1, it could go either way,” Dr Taubenberger said. “There is still a risk that H5N1 could become pandemic through reassortment with a contemporary human flu strain, but it’s also possible that it could completely adapt to humans like the virus did in 1918.”

The discoveries come a week after David Nabarro, who was appointed last Thursday as the UN co-ordinator for avian and human influenza, said that avian flu had the potential to kill 150 million people.

Sir Liam Donaldson, Britain’s chief medical officer, then said that this country’s contingency plans assume that at least 50,000 people would die here in such an outbreak.

Indonesia, the fourth country to suffer human cases of H5N1 flu, reported a seventh death yesterday, of a 23-year-old man, though only three of these are confirmed to have been caused by the virus.

Dr Taubenberger’s study, published in the journal Nature, has mapped the genetic code of the H1N1 Spanish flu strain, using viral material from a female victim preserved in permafrost in Alaska. Another group, led by Terrence Tumpey, of the US Centres for Disease Control (CDC), advised by Dr Taubenberger, used this information to reconstruct the H1N1 virus. These results are published in the journal Science.

Vials of the re-created virus are stored in a secure CDC laboratory. Julie Geberding, director of the CDC, said that producing the virus carries little risk to the public as human populations have a residual immunity to the H1N1 strain, making it unlikely that an accidental release could itself start a pandemic.

Dr Taubenberger said: “In the case of the H5N1 viruses we do find some parallels. This suggests the possibility that the H5 viruses are being exposed to some human adaptive process and might be acquiring these changes, in the sense that they might be going down a similar pathway that led to 1918.”

PANDEMICS PAST

Other flu pandemics struck in 1957 (the “Asian flu”) which killed about four million, and in 1968 (the “Hong Kong flu”) which killed about one million

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