THE “Spanish flu” virus that killed more than 20 million people in 1918-19 may have originated in birds then jumped the species barrier to human beings, something that scientists fear could happen with the avian flu outbreak in Asia.

Research by a British-led team of scientists who mapped the structure of the virus sheds important light on one of the world’s biggest pandemics. It has revealed the mechanism by which the killer flu infected human cells, providing valu-able clues for experts monitoring the danger posed by modern strains of the virus.

Surveillance centres will use the findings to analyse new variants of influenza as they emerge in bird populations to determine whether they have the potential to enter human cells in the same way and start a pandemic similar to the 1918 outbreak.

They will do little, however, to help to predict the threat posed by the present strain, which has led to 15 deaths, because it has a different structure from its 1918 cousin. In the study, an international team led by Sir John Skehel, director of the Medical Research Council’s National Institute for Medical Research (NIMR) in London, analysed the spiky proteins that the influenza virus uses to bind to human cells. Details of their work are published today in the journal Science.

The scientists used viral DNA sequences from biopsies taken from American soldiers who died in the pandemic, which were then examined using a technique known as X-ray crystallography.

This procedure revealed the three-dimensional structure of the 1918 virus’s spiky surface molecules, known as hemagglutinin (HA) proteins.

The HA proteins produced by human and bird viruses generally bind to different types of cell receptors, making it very difficult for avian flu strains to infect people and vice versa.

In rare cases where human beings do contract an avian virus, it is not usually possible for them to infect others. In the 1918 outbreak, however, the HA protein of an avain flu appeared to have mutated, allowing the virus to bind to human cell receptors and be transmitted from one person to another. Sir John said that the discovery was extremely significant for modern flu surveillance because it flagged up a type of HA protein spike structure that is particularly dangerous. If another strain with similar characteristics emerged, the world would be forewarned, giving scientists a head start on vaccine development and prevention strategies.

“This paper is important because of the knowledge it brings about how these viruses which originate in birds can jump to human beings,” he said. “This allows us to track and monitor the changes in the virus for public health purposes, even though it does not allow us to predict or prevent future forms of flu.

“If something with similar properties were to emerge, we would keep close tabs on it. The results don’t mean that anything without these features is harmless —there are many other configurations that can be damaging — but they will make an important contribution to surveillance.”

The results will not help investigations of the present avian flu outbreak because its HA proteins are of a type known as H5, while the Spanish flu was of the H1 variety.

“It will not have an immediate impact on the situation unfolding in the Far East with the chicken flu known as H5 since, from our previous work, we know that the 1918 and the H5 hemagglutinins are quite different,” Sir John said.

A separate study, also published in Science today, has all but confirmed that birds were the source of the 1918 strain. The analysis, led by Ian Wilson of the Scripps Research Institute in La Jolla, California, found the structure of the virus had more in common with bird strains than those that typically infect humans or pigs. “It looks more like an avian virus with some human characteristics,” Professor Wilson said.

All the worst outbreaks of flu in the past century originated from birds. The 1957 Asian flu and the 1968 Hong Kong flu began in poultry in South-East Asia and Sir John said he suspected the region was the source of the 1918 pandemic.

Scientists are hoping to improve their understanding of the 1918 pandemic still further by exhuming the body of a 20-year-old British victim. Phyllis Burn, an army officer’s daughter from Strawberry Hill, southwest London, was buried in a cemetery in Twickenham 85 years ago.

She was laid to rest in a lead coffin which, if properly sealed, would have been virtually airtight. Scientists hope that her internal organs may be sufficiently preserved to allow tissue samples to be taken from her lungs.

John Oxford, who is leading the team from Queen Mary’s School of Medicine in London, still has to get final permission to remove Miss Burn’s body from the church authorities in charge of the cemetery.

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