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The avian flu virus H5N1 tends to target the lungs, causing overwhelming and often fatal alveolar damage in infected humans. Researchers using sensitive molecular techniques have also found traces of the virus in other organs, most recently in the brain, intestines, and lymph nodes of two Chinese patients. One of them, a 24 year old woman, was four months pregnant when she died. At autopsy, the researchers found evidence of the virus in the baby's lungs, circulation, and liver. Vertical transmission from the mother is the likeliest explanation, and it sets H5N1 apart from common human flu viruses, which are thought to be harmless to the fetus.
The presence of H5N1 in the intestine fits well with the diarrhoea that often accompanies the infection, says a linked comment (p 1106). Others have already reported viral RNA in faecal samples from infected people, with obvious implications for controlling spread of the disease.
It now seems clear than H5N1 spreads far beyond the lungs in humans and may even cross the blood-brain barrier. We still don't know why the infection is so lethal, but it may be something to do with our immune response. The immunologically naive fetus in this report was infected but had no organ damage.