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Study shows why 1918 flu epidemic was so deadly
Updated: 2004-02-06 15:05

The 1918 flu virus, which killed 20 million people around the world, was probably so deadly because of a unique bird-like protein, U.S. and British scientists reported on Thursday.

Like a current outbreak of bird flu in east Asia, the 1918 influenza appears to have jumped from birds to people with little change, they wrote in this week's issue of the journal Science.

But unlike the 1918 flu, the current bird flu, which has killed 16 people, so far has not developed the mutation that allowed influenza to decimate human populations 80 years ago.

"What (this study) says is this transmission between birds and humans seems to be able to happen in more than one way," John Skehel of Britain's Medical Research Council, who led one study, said in a telephone interview.

Two teams of researchers analyzed samples of the virus from the 1918 outbreak and said it bears the clear hallmarks of a bird virus that mutated very little before jumping from birds to people.

Health officials in China, Thailand, South Korea and Vietnam are scrambling to control the current outbreak of avian influenza, known as H5N1. It is lethal to people, which is often the case when viruses leap from one species to another.

In 1997 when it first appeared in Hong Kong it was contained very quickly because it did not spread from human to human, but only from birds to people.

So far this year only 16 people have been killed, but there is some evidence it may have begun spreading from person to person. If that happens, experts fear the virus has the potential to be as bad as the 1918 epidemic.

Understanding just what it is about the viruses that makes them deadly, and what makes them able to live and spread among humans, will be key to controlling or pre-empting future epidemics, the researchers noted.


Skehel's team and another led by Ian Wilson at the Scripps Research Institute in La Jolla, California looked at bits of the virus extracted from the bodies of victims, some buried in Alaska permafrost and others saved in laboratory jars.

They looked specifically at a part of the virus called hemagglutinin, which is a protein the virus uses to infect cells. Each strain of virus has a unique hemagglutinin structure, and scientists believe small mutations of the protein are what allows the virus to infect new species.

The 1918 virus was an H1 virus -- different from H5N1.

They found it had some unique structures that may have given it "novel mechanisms" for infecting people, Wilson and colleagues wrote. This may explain why the 1918 epidemic killed so many young, healthy adults.

And this explains why the current avian flu outbreak has, so far, not lived up to fears, said Skehel.

"Presumably, what's blocking this current flu from spreading person-to-person is that its hemagglutinin structure has not yet evolved such that it can efficiently infect humans," Skehel said in a statement.

"This tells us more about the transmission of infections from birds to humans," he added.

"However, it will not have an immediate impact on the situation currently 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."

He said scientists should be testing birds for various forms of influenza to see what else may be lurking out there with the potential to infect people.

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