After wandering amid cages of birds and rabbits at an open-air...

After wandering amid cages of birds and rabbits at an open-air market in Hanoi and visiting a Haiphong family sickened by bird flu, the United States' top health official came to a grim conclusion: Preventing the start of a global flu outbreak is just about impossible.
If the virus mutates to a form easily spread among people. It could skip across borders and oceans, killing millions and crippling entire nations.

"Can we create a network of surveillance sufficient enough to find the spark when it happens, to get there fast enough?" he said. "The chances of that happening are not good."

Many epidemiologists say the bird flu poses the single most dangerous disease threat to humanity.