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Bird Virus Linked to 1918 Flu Pandemic

Researcher: Jump to humans was 'simple'

FRIDAY, Feb. 6, 2004 (HealthDayNews) -- If new research on the 1918 Spanish flu epidemic is to be believed, scientists in Asia have good reason to worry about the avian flu that has spread to humans there in recent months.

The Spanish virus killed more people than World War I, and researchers now suggest it may have started in birds.

According to two studies released in this week's issue of Science, there's not much difference between the 1918 flu strain and an avian virus. The similarities, in fact, may have made it harder for humans to fight off the virus by fooling their immune systems into thinking the germs were harmless.

This could be bad news for the future, especially as doctors cope with the recent outbreak in Asia. The Spanish flu's leap from birds to people was "simple," says Ya Ha, an assistant professor of pharmacology at Yale University and co-author of one of the studies. There are 15 avian flu viruses, he adds, and "every one... has the potential to jump across the species barrier."

The 1918 influenza epidemic killed an estimated 20 million to 40 million people around the world, including at least 500,000 in the United States. In an odd twist, about half of those who died were young, healthy adults, perhaps because older people had developed immunity to a similar virus earlier in their lives.

The Spanish flu virus is now extinct, but researchers can study its genetic makeup by examining infected tissues from the bodies of American soldiers and from an Intuit woman whose body was preserved in the permafrost of Alaska.

While some scientists have argued the Spanish flu had nothing to do with birds, others say it somehow mutated and "jumped" from birds to humans.

Supporting the second theory, both studies found a protein called hemagglutinin, part of the structure of the 1918 flu virus, is similar to that of bird viruses. The human virus "looks more like an avian virus -- with some human characteristics," Ian Wilson, co-author of the second study, says in a statement. Wilson, a molecular biology professor at the Scripps Research Institute, worked with other American researchers on his study.

According to the researchers, the human virus may have been so similar to the bird virus that the bodies of victims didn't recognize it as a threat.

Ha says scientists have also connected avian flu viruses to later human outbreaks -- the Asian flu of 1957-1958 and the Hong Kong flu of 1968-1969. Scientists think it's possible the later flu epidemics weren't as deadly as the Spanish flu because the two avian viruses involved had to go through more mutations to infect humans.

"They really have to bite the bullet and make a major change," Ha explains. As a result, human immune systems may have had an easier time recognizing them as enemies because they don't look as much like bird germs.

The avian virus suspected in the Spanish flu epidemic, by contrast, "is basically in a state which is more ready to become infectious to humans," Ha says.

Even so, the findings suggest that all 15 types of avian flu can fairly easily make the leap to humans, Ha says: "It doesn't take a lot of change for them to do that."

However, Ha doubts that a future influenza epidemic related to avian flu would be as deadly as the Spanish flu. "Medical science has advanced so much that I don't think anything that bad would happen," he says.

More information

For more about avian flu, try the U.S. Centers for Disease Control and Prevention. To learn about the Spanish flu, visit Stanford University.

SOURCES: Ya Ha, Ph.D., assistant professor, pharmacology, Yale University, New Haven, Conn.; Feb. 5, 2003, online edition, Science
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