Sunday, February 04, 2007

Bird Flu Pandemic Only Two Key Mutations Away

A revealing, troubling story from the Daily India which seems to have missed the attention of most of the world's media. Maybe it was too complicated for mainstream consumption : research has revealed that the difference between a flu virus that kills millions, and one that kills only a few comes down to just two amino acid changes.

The finding could allow scientists to stay one step ahead of a H5N1 flu pandemic, by screening for the specific mutations that would enable it to spread.

A new study investigating the difference between the 1918 pandemic flu virus - which killed at least 50 million people - and a virus which kills but does not spread, turned out to be two small mutations on the virus's surface.

Just two amino acids - the building blocks of protein - need to change on the virus's surface in order to allow it to spread easily between people, the researchers found.

Haemagglutinin, the main surface protein on flu viruses, binds to sugars on cells in the nose and lungs; the virus then enters the cells and replicates. Bird flu prefers a sugar called 2,3-sialic acid. Flu adapted to mammals attaches better to 2,6-sialic acid. Mammals have the 2,3 sugar deep in their lungs, but 2,6 in the nose and throat.

H5N1 prefers 2,3. It had been thought that that was why it causes a devastating deep-lung infection in humans, but does not spread between people, because it does not bind and replicate in the nose.

(Ed : But apparently, this is not how the 1918 virus managed to kill so many people).

What a virus needs to spread, the CDC team concluded, is an ability to bind 2,6 sugars, whether or not it needs this to replicate. What this binding does do is not clear. One clue, they speculate, is that ferrets with non-contagious viruses - H5N1, or mutant 1918 - do not sneeze. Contagious ferrets do.

...what is important is what this tells us about how the next pandemic might begin. The same mutations that made the 1918 flu contagious will not apply to H5N1, as it has a different haemagglutinin.

However, the CDC results suggest finding out what mutations make H5N1 bind to 2,6-sialic, as those could make it contagious.

No comments: