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Scientists: 1918 Killer Flu Was a Bird Flu

Ominous Changes in Current Bird Flu Echo 1918 Virus
By
WebMD Health News
Reviewed by Louise Chang, MD

Oct. 5, 2005 -- Scientists who re-created the 1918 Spanish flu say the killer virus was initially a bird flu that learned to infect people. Alarmingly, they find that today's H5N1 bird flu is starting to learn the same tricks.

The work involves researchers from the Armed Forces Institute of Pathology (AFIP), the CDC, Mount Sinai School of Medicine, and the U.S. Department of Agriculture. Jeffery K. Taubenberger, MD, PhD, chief of molecular pathology at the AFIP, is one of the study leaders.

"These H5N1 viruses are being exposed to human adaptive pressures, and may be going down a similar path to the one that led to the 1918 virus," Taubenberger said in a news conference. "But the H5N1 strains have only a few of these mutations, whereas the 1918 virus has a larger number."

In 1918-1919, the so-called Spanish flu killed some 50 million people -- including 675,000 Americans. Most of the victims were healthy people in the prime of life.

The researchers' findings -- published this week in the journals Nature and Science -- come from a remarkable decade-long effort to unlock the secrets of the most deadly flu bug ever known.

To do this, the researchers used a technique called reverse genetics to re-create a living 1918 virus. To do this, they gathered viral DNA from the preserved tissues of people who died in 1918 and 1919 -- including a woman whose body was frozen in the Alaskan permafrost.

Past Virus, Future Virus

The resurrected virus now lives in high-level containment within the CDC. But that's not what worries public health officials.

The 1918 flu, analysis shows, is a bird flu that learned how to spread among humans. Genetic analysis shows that the deadly H5N1 bird flu now circulating in Asia seems to be learning the same thing.

Like the 1918 virus, the milder pandemic flu bugs of 1957 and 1968 also had bird flu genes. But they picked up the ability to spread in humans by swapping genes with a human flu virus. That could still happen to the H5N1 bird flu. But even if it doesn't, the bug seems to be slowly adapting to humans.

The good news is that the H5N1 flu bug still has a long way to go. The 1918 bug seemed to need several changes in every one of its eight genes. The H5N1 virus is making similar changes but isn't very far along.

"So, for example, in the nuclear protein gene we speculate there are six genes crucial [for human adaptation]," Taubenberger says. "Of those six, three are present in one or another H5N1 strain. But usually there is only one of these changes per virus isolate. That is true of other genes as well. You see four, five, or six changes per gene in the 1918 virus, whereas H5N1 viruses only have one change or so. It shows they are subjected to similar [evolutionary] pressures, but the H5 viruses are early on in this process."

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