As Dr. Sreyleak Luch drove to work on the morning of Feb. 8, through busy sunbaked streets in Cambodia’s Mekong river delta, she played the overnight voice messages from her team. The condition of a 9-year-old boy she had been caring for had deteriorated sharply, and he had been intubated, one doctor reported. What, she wondered, could make the child so sick, so fast?

"And then I just thought: H5N1,” she recalled. "It could be bird flu.”

When she arrived at the airy yellow children’s ward at the provincial hospital in Kratie, she immediately asked the child’s father if the family had had contact with any sick or dead poultry. He admitted that their rooster had been found dead a few days before and that the family had eaten it.