The speed of its migration, and the vast area it has infected, has forced scientists to concede there is little that can be done to stop its spread across the globe.
"We expected it to move, but not any of us thought it would move quite like this," said Dr. David Nabarro, the United Nations' coordinator on bird flu efforts.
The hope was once that culling millions of chickens and ducks would contain or even eradicate the virus. Now, the strategy has shifted toward managing a disease that will probably be everywhere. Officials are hoping to buy a little more time to produce human vaccines and limit the potential economic damage.
"We cannot contain this thing anymore. Nature is in control," said Robert G. Webster, a virologist at St. Jude Children's Research Hospital in Memphis, Tenn., who has been studying the virus since it emerged in 1997.