Two Threatening Bird Flu Mutations
Scientists ID Bird Flu Mutations Likely to Trigger Human Pandemic
Nov. 15, 2006 - Either of two simple bird flu virus mutations could trigger
a deadly pandemic, Japanese scientists warn.
Both mutations already have popped up in humans infected with the H5N1 bird
They've been seen in bird flu viruses isolated from two people in Azerbaijan
and from one person in Iraq, according to the Japanese scientists. Neither
mutation has been seen among the more than 600 H5N1 viruses isolated from
The two human mutations give the bird flu virus the ability to attach to
human cells. It's the kind of mutation seen early in the 1918, 1957, and 1968
flu pandemics, warn Shinya Yamada of the University of Tokyo and
Fortunately, the H5N1 viruses carrying these mutations do not appear to have
caused any outbreaks of human-to-human transmission.
But these mutants seem capable of replicating in humans -- "an essential
indicator of pandemic potential," the researchers report.
Flu viruses attach to receptor molecules on the outside of cells that line
Bird flu viruses use a receptor called SAalpha2,3Gal. Human flu viruses use
a closely related receptor called SAalpha2,6Gal.
Previous flu pandemics came from bird flu viruses. Each time, the pandemic
took off when the viruses learned to attach to human airway cells.
Yamada and colleagues manipulated H5N1 viruses in the laboratory to see what
it would take to make a bird flu virus do this. They found that either of two
mutations -- single amino-acid changes at specific places in the viral DNA --
did the trick.
The researchers suggest that health authorities look for these mutations in
bird flu viruses isolated from humans. If found, they could be an early warning
of a budding pandemic.
Yamada and colleagues report their findings in the Nov. 16 issue of the