China has closed its nature reserves after the bird flu turned up in migratory birds. Meanwhile, in Vietnam, another person has apparently died from bird flu. The death toll from the current outbreak in Southeast Asia now stands at 54.

Vietnam's health inspectors visit local markets and breeding farms on a daily basis. They work well into the night checking shipments of livestock. The country is taking the threat of avian flu very seriously. But many poor farmers still try to cover up outbreaks in their flocks so government inspectors won't kill their healthy birds. This is the grave of 10-year-old Bo Thi Huang. She died of bird flu within days of helping her family bury some infected chickens. Her grandfather says they knew the danger and now they are paying the price.

So far, most of people who have contracted avian flu have had close contact with infected birds. But Dr. Somchai Peerapakorn from the World Health Organization says evidence exists that the virus is already mutating, that direct human-to-human transmission is a matter of time.

"Based on history, based on scientific evidence, it will be serious, and deadly. Deadly," says Dr. Somchai Peerapakorn.

More than half of those who have contracted the virus have died. Dr. Jeremy Farrar, from the Hospital for Tropical diseases in London, says in these x-rays from a Vietnamese Hospital, the black area is normal lung tissue. The white areas on this x-ray shows lung tissue that has been destroyed by the virus.

"If this virus retained its ability to destroy tissue like this and then developed the ability to go from me to you, then we really are in a nightmare scenario," says Dr. Farrar.

That is why Vietnamese health inspectors are working day and night. They know the only way to prevent a human epidemic is to defeat the epidemic in birds. And that victory is far from certain.