To date, roughly 103 people have been infected with the H5N1 avian
influenza virus–or bird flu. Yet few, if any, of them have spread the
disease to other humans.

A virus’s ability to spread is the key to its
ability to create a pandemic. New research shows that this bird flu
currently lacks the protein key to unlock certain cells in the human
upper respiratory tract, preventing it from spreading via a sneeze or a
cough.

Virologist Yoshihiro Kawaoka of the University of Wisconsin and
University of Tokyo and his colleagues tested strains of H5N1 isolated
from respiratory tissue in the noses, throats and lungs of infected
humans. Although regular human flu viruses bound easily with the
receptors found in the nose and throat cells, H5N1 strains attached
only to those receptors on cells found in the deepest regions of the
lungs.

David Biello
ScientificAmerican.com