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Wednesday, March 22, 2006

URTI v. LRTI

Some explanation for why H5N1 isn't spread easily for humans...for now.
The Japanese-American team found that, as expected, H5N1 avian flu is drawn to the 2,3 receptors. Luckily for humans, they also found that 2,3 is most abundant on cells within the alveoli, the most remote, microscopic branches of the lungs' "respiratory tree."

H5N1 was much less likely to bind to cells in the upper respiratory tract.

In contrast, common human flu strains prefer to bind with the 2,6 receptor, which is found in plentiful numbers on upper respiratory tract cells. That makes sense, experts say, because every time humans cough or sneeze, droplets from this area are easily expelled into the air, making human-to-human transmission of ordinary seasonal flu possible.

H5N1 colonizes a much deeper, tough-to-access region of the lung -- making infection more difficult to spread and treat in humans, the researchers said.

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