China has joined the growing number of Asian countries battling a bird flu virus that could be just a mutation away from becoming a worldwide scourge among humans.
China found the bird flu in dead ducks on a southern farm in Dindang, about 60 miles from Vietnam, according to the official Xinhua news agency. The Chinese government said authorities were investigating possible cases of the disease in two other provinces.
About 14,000 birds within a 2-mile radius of the farm were slaughtered, and others in the area were quarantined.
Avian influenza has been found in bird populations in 10 countries, and at least eight people who contracted the virus after direct contact with the infected animals have died. Millions of birds have been destroyed in an effort to stop the virus from spreading.
Yesterday, the World Health Organization reported the death of a 6-year-old boy in Thailand, the second child to die of the disease there this week.
No one knows how serious the outbreak will become. But health officials fear that the avian flu virus may combine with a human flu virus to create a new, more infectious form that is easily transmitted from person to person. The process - something of a genetic mix-and-match - is known as "reassortment."
"These viruses are prone to evolve over time, so there's always the possibility that transmission could become more efficient," Dr. Julie L. Gerberding, director of the federal Centers for Disease Control and Prevention in Atlanta, said in a conference call with reporters yesterday.
Only Vietnam and Thailand have reported human cases of the disease, which can cause typical flu-like symptoms as well as severe respiratory distress. But health authorities have found infected birds in Cambodia, Indonesia, Japan, Laos, Pakistan, South Korea, Taiwan, Thailand and Vietnam - as well as China.
So far, the disease is afflicting only Southeast Asia, but its rapid spread there has sounded alarms around the world, particularly in an age of international air transport. Last year, the newly emergent virus re- sponsible for severe acute respiratory syndrome, or SARS, affected patients in about 30 countries on five continents.
"The more [avian flu] circulates in chickens and the more that you get this occasional transmission to humans directly from chickens, the more likely it is that we may see the virus change, by one means or another, and begin to spread from human to human," said Dr. Arnold S. Monto, professor of epidemiology at the University of Michigan School of Public Health, a World Health Organization-designated influenza center.
Public health officials seem to have more questions than answers about the virus, which has never before infected flocks in so many countries simultaneously. Among researchers' many concerns are whether children are more susceptible than adults and whether people can carry the virus without getting sick.
Already there have been setbacks. WHO officials said last week that the virus appears to be resistant to two drugs traditionally used to treat influenza, amantadine and rimantadine. What's more, there is no existing vaccine because the current virus strain is different from that detected in a 1997 outbreak.
All so-called "type A" influenza viruses are known for their tendency to change forms, in part because they are genetically unstable. They also lack mechanisms for "proofreading" and repairing errors that occur as they replicate in humans and animals.
"We really have had to start from scratch and work as quickly as possibly to get a vaccine candidate developed," said the CDC's Gerberding.
That process could take weeks or, more likely, months.
"There's not really a way to speed it up any faster than we're already working on it," she said.
Whether any vaccine they develop is mass-produced will depend on the course of the disease in Asia and the success of containment, Gerberding said.
Avian flu viruses, as their name implies, usually infect only birds. The first known transmission from birds to humans occurred in Hong Kong in 1997, when 18 people were hospitalized and six died. Officials killed all of the island's chickens - about 1.5 million - over three days to stop further spread, a move public health officials credit with stemming a more serious outbreak.
Last year, bird flu broke out among poultry in the Netherlands, sickening more than 80 people and killing a veterinarian. In a separate incident, two members of a Hong Kong family that had recently visited southern China became infected, and one died.
As far as health officials know, the virus is not transmitted through chicken eggs or meat. Rather, the infected birds spread the virus in saliva, feces and nasal secretions, which in turn can sicken humans in close contact.
The best way to prevent the virus' spread, then, is by eliminating the source. Vietnam has reportedly killed more than 3 million chickens, Thailand about 10 million.
"By doing that, you are going to decrease the source of infection to humans," said Dr. Marlo Libel, regional adviser on communicable diseases for the Pan American Health Organization in Washington. "This is the most important part of the prevention at this point."
Though the current avian flu outbreak may not turn out to be the next influenza pandemic, some experts say the world is due - or overdue - for one. Three or four such pandemics are generally expected to occur every century. The last three were the "Spanish flu" of 1918-1919, the "Asian flu" in 1957-1958 and the "Hong Kong" flu in 1968-1969.
Despite the attention SARS got last year, the avian flu is potentially much more dangerous, said Dr. Ruth Karron, an associate professor of international health at the Johns Hopkins Bloomberg School of Public Health.
"This is a virus that causes tremendous amount of morbidity and mortality," she said. "If it can spread readily from person to person, then I think we're in a lot of trouble."
The Associated Press contributed to this article.