BIRD flu can be fatal in humans, but it is also quite hard to catch 鈥� and the reason for both lies deep in our lungs.
Bird flu infects birds, and human flu infects humans, when the virus binds to a sugar molecule on the surface of the host鈥檚 cells 鈥� a different sugar for the two kinds of viruses. This week Yoshihiro Kawaoka and colleagues at the University of Wisconsin-Madison report that while cells in our noses, throats and lungs have only the sugar that matches human flu, we also have the 鈥渂ird鈥� sugar on cells in the alveoli, the delicate air sacs in our lungs.
It is the alveoli that are destroyed in the lethal pneumonia caused by H5N1 bird flu, which is why it is fatal to humans. H5N1 is hard for us to catch because it doesn鈥檛 bind readily to human noses and throats, where flu viruses usually enter and exit the body (Nature, DOI: 10.1038/440435a).
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To become a human pandemic, H5N1 must learn to bind to the 鈥渉uman鈥� sugars. A team led by James Stevens at the Scripps Research Institute in La Jolla, California, reports that some mutations in the H3 flu family do make this possible. Such a mutation in H5N1 might allow it to spread rapidly between humans (Science, DOI: 10.1126/science.1124513).
