Why bird flu has been kept at bay
- This is good news. Perhaps the idea that we are only one or two small mutations away from Bird Flu evolving so it can jump from human to human is incorrect.
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Scientists say they have identified a key reason why bird flu has so far not posed a widespread menace to humans.
So far, the H5N1 strain has mainly infected birds and poultry workers, but experts fear the virus could mutate to pass easily from human to human.
However, Massachusetts Institute of Technology found that to enter human respiratory cells the virus must first pick a very specific type of lock.
The study appears in the journal Nature Biotechnology.
The researchers say their discovery may help scientists better monitor changes in H5N1 - and find better ways to fight it.
Flu viruses attack by binding sugar chains, called glycans, that line the airways and lungs.
Latching on
The chemical linkages between the sugar molecules in these chains differ between humans and birds.
Until now it has been assumed that bird flu viruses would be adapt to humans simply by acquiring mutations that enable them to attach to the human types.
But Dr Ram Sasisekharan and colleagues found this step depends on the shape assumed by the flexible sugar chains rather than the type of linkage.
Bird flu viruses currently require cone-shaped glycans to infect birds, so the umbrella shape found in humans has protected most of us from avian flu.
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