BANGKOK, Thailand - Thai officials announced yesterday that two boys had become infected with avian influenza and that six more people were suspected of having it.
The acknowledgment confirms that the deadly disease has now spread across Southeast Asia, and it raised fears among doctors of a possible global influenza epidemic if the virus evolves to pass easily from person to person, instead of just from contact with infected birds.
Vietnam has reported five confirmed cases in people near Hanoi, all of whom died before the lab tests were even finished, and is testing seven additional suspected cases across the country. Chickens from South Korea and Japan to Vietnam and Thailand have been dying from the same disease.
Doctors think all of the reported human cases have been contracted from contact with live chickens or their waste. But the World Health Organization warned repeatedly this week that if someone becomes infected with the bird flu and the human flu at the same time, the viruses could swap genetic material and the result could spread quickly among people.
Nobody has tried to predict how long this might take, if it happens at all, but the possibility has deeply worried WHO officials. All three of the big influenza epidemics of the 20th century are thought to have started in birds. The H5N1 strain now killing chickens across east Asia and infecting some people in Southeast Asia appears to be especially lethal.
"Of all the avian influenza viruses, which normally cause infection in birds and pigs only, the H5N1 strain may have a unique capacity to cause severe disease, with high mortality, in humans," the WHO said in a statement Thursday.
Jakrapob Penkair, the Thai government's chief spokesman, said the government was working with the country's biggest agricultural businesses to control the spread of the disease, killing chickens at farms where infections took place and halting the sale of these chickens. It is testing for bird flu all Thai chicken exports to the country's four main export markets, Penkair said. These markets are Japan, which buys half of Thailand's chicken exports; the European Union, which buys another third; and the United States and Brazil, which buy much smaller quantities.
Japan temporarily suspended the import of Thai chickens Thursday, and the European Union did so yesterday. The World Health Organization has said that while the feces, saliva and breath of the chickens may contain the virus, there was no evidence that the meat can cause illness.
Laos said earlier this week that it was investigating chicken deaths but thought them to be bird cholera. Agence France-Presse yesterday reported from the Indonesian island of Bali that a provincial official had acknowledged the death of thousands of chickens, but he attributed it to another virus, the Newcastle virus. Cambodia has said that it is looking into chicken deaths there but does not know their cause. There have been unconfirmed reports of chicken deaths in Myanmar as well; Penkair said that infected chickens had been found in "three or four" western provinces of Thailand, toward the Myanmar border.
China has continued to deny, most recently on Thursday, that it has any cases of bird flu. But Hong Kong officials said Wednesday that they had found a dead peregrine falcon near the mainland China border that was infected with the disease.
The H5N1 virus was first documented to have jumped to people in 1997, when sick chickens infected 18 people in Hong Kong, including previously healthy adults, killing six of them. All 1.5 million chickens in the territory were slaughtered within three days before the disease could evolve further, a step some influenza experts have credited as preventing a global epidemic among people.
Two residents fell sick with the disease after visiting their nearby hometown in mainland China last year, and one of them died.
Little progress has been made on a vaccine. Current flu vaccines are thought to provide no protection. While a possible vaccine was prepared last year from the virus that infected the two Hong Kong residents, the WHO announced Thursday that the virus had mutated so much in the last year that the vaccine would not be effective, forcing scientists to pursue a month-long effort to design a new vaccine.
Mass producing a vaccine for H5N1 is especially difficult for technical reasons, moreover, leaving flu experts to warn that it will likely be possible to immunize only a small part of the world's population next winter. Prescription flu medicines to relieve the symptoms of H5N1 have limited effect.