Scientists Find How Bird-Flu Virus 'Humanizes'
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This is ALL THINGS CONSIDERED from NPR News. I'm Robert Siegel.
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Scientist studying the Asian Bird Flu said they're a step closer to understanding exactly how the virus would have to change to touch off the next flu pandemic, and they say they hope to have an early warning system soon to detect those genetic changes. NPR's Richard Knox has this report.
RICHARD KNOX reporting:
The question among flu researchers these days is this...
Mr. JEFFREY TAUBENBERGER (Armed Forces Institute of Pathology, Washington): What kind of changes have to occur to allow a bird virus to jump the species barrier and adapt to humans?
KNOX: Jeffrey Taubenberger of the Armed Forces Institute of Pathology in Washington knows as much about flu viruses as nearly anybody. He led the project to reconstruct the virus that killed tens of millions of people in 1918. Taubenberger says the first place to look for clues about what makes a pandemic virus is in a protein molecule on the outside of every flu virus. It's called hemoglutonin.
Mr. TAUBENBERGER: Changes in hemoglutonin are clearly very important and probably right on the very top of the list of the most important changes to worry about because that allows the virus to gain entry into the cell.
KNOX: Scientists at the Scripps Research Institute in California took a close look at the hemoglutonin from three flu viruses that caused pandemics in 1918, 1957, and 1968. James Paulson of Scripps says they zeroed in on how each virus got into the cells of its host. In this case the human cells that it's trying to infect.
Mr. JAMES PAULSON (Scripps Research Institute, California): The first important thing to understand is that flu virus recognizes a sugar on a host cell. And all flu viruses recognize that sugar in order to bind the cells.
KNOX: The sugar that coats bird cells is subtly different from the sugar on human cells. So if a bird virus is going to become a human virus, it's got to make a genetic change or mutation so it could latch on to the sugar on human cells.
Mr. PAULSON: The amazing thing is it only takes one or two amino acid mutations for that change to occur.
KNOX: Amino acids are the basic building blocks of all proteins. The Scripps team took the mutations that converted the 1918 virus's hemoglutonin from a bird to a human type and put those mutations into the Asian bird virus now circulating on three continents. Its hemoglutonin is an H5 type.
They wanted to see if those 1918 mutations would give the H5 virus the ability to infect human cells. It didn't. But when they took two mutations from the 1968 flu virus and put them into today's Asian bird flu virus, they saw something different.
Mr. PAULSON: It didn't provide a full switch to the human type, but it provided a partial switch. This might be sufficient. This might be a path for the H5 virus to gain a foothold.
KNOX: Dr. Anthony Fauci of the National Institutes of Health says the new report, which appears in the journal Science, is important.
Dr. ANTHONY FAUCI (National Institutes of Health): But I think we have to underscore that does not mean that if the virus naturally mutates to that type, that it will then have the capability of going efficiently from human to human. Because the ability to go efficiently from human to human is a much more complicated, not very well understood phenomenon.
KNOX: It probably involves changes in many of the flu virus's eight genes. Still, the authors of the new report think if the H5 bird virus gains a foothold in human cells, it might acquire the other mutations it needs to spread explosively among people. Other flu experts agree, so they're beginning to use the Scripps test to screen bird flu viruses that have infected humans. The test looks for bird viruses that can recognize sugars on human cells. So far none have popped up. That's reassuring, but it doesn't mean the Asian bird flu virus won't develop the crucial mutations. If it does, the new test could give advanced warning that a pandemic virus is in the works. Richard Knox, NPR News.
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