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Cold, Flu, & Cough Health Center

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Scientists: 1918 Killer Flu Was a Bird Flu

Ominous Changes in Current Bird Flu Echo 1918 Virus

Past Virus, Future Virus continued...

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."

How Much Time Do We Have?

How long does this process take? Nobody knows. Taubenberger says the 1918 bird virus appeared in humans "a couple of years" before 1918. But how long it took the virus to jump species from birds to humans is unknown.

There is one ominous sign. It's in a flu gene protein called PB2. A single change in this gene makes H5N1 extremely deadly to mice. The same single change helps bird flu to adapt to mammals.

For example, the change in PB2 was seen in six of the seven H5N1 viruses spreading among captive tigers in Thailand. The same change popped up in the only human to die during an outbreak of another bird flu, H7N7, in the Netherlands. And it's present in recent H5N1 viruses from humans in Vietnam and Thailand and from wild birds in China.

"The fact that [gene] changes identified in the 1918 analysis are also seen in highly pathogenic avian influenza strains of H5N1 and H7N7 is intriguing, and suggests that these changes may facilitate virus replication in human cells and increase pathogenicity," Taubenberger and colleagues write in their Nature paper.

New Information to Help Fight Flu

Scary as it is to take a close-up look at killer flu bugs, it's a good thing to do. Knowing the enemy helps us find ways to defeat it, says Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Diseases.

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