Bird Flu Spreads in Thailand; New Mutations Seen

Health authorities said Thursday that avian flu had been detected in chickens and ducks in Thailand’s capital, bringing the number of provinces affected to 10 -- out of 76 -- and raising fears of a new human epidemic like the one that killed 24 people earlier this year.

Outbreaks also have been reported in China and Vietnam. Two scientific papers published in the last week hinted that the virus was more easily infecting mammals, presumably including humans, and authorities fear that another mutation or two will allow it to spread readily from human to human.

More than 40,000 chickens have been killed in Thailand to halt the spread of the disease. Deputy Prime Minister Chaturon Chaisang said chickens and ducks on farms throughout the country would be randomly tested for the virus July 31.

Authorities have already ordered immediate culling on any farm where more than 10% of the chickens have died of unidentified causes.

Farmers this week have called for the use of a vaccine that offers chickens some protection against the virus, but Chaturon said the government would not permit its use until more was known about its safety and effectiveness. Some scientists fear that the vaccine, which does not completely block infection, could lead to mutations that would increase the risk to humans.

Chinese authorities have been monitoring 37 people for avian flu symptoms after finding the disease on a poultry farm this week, according to a report in the state-run China Youth Daily. So far there have been no reports of human infection in Thailand amid the current outbreak.

Thailand has historically been one of the largest exporters of chicken in Southeast Asia. About 100 million chickens and ducks were culled in the flu outbreak earlier this year, devastating the poultry industry. Eight people died in Thailand and 16 in Vietnam in the outbreak.

Farmers and government officials eradicated the outbreak in commercial flocks but have been unable to halt its spread in wild fowl, which are thought to be the major reservoir of infection.

Microbiologist Yi Guan of the University of Hong Kong and his colleagues reported last week in the online version of the journal Nature that the virus responsible for the current outbreak developed in domestic ducks in the southern provinces of China and spread throughout the region via wild ducks and other fowl.

Over the course of five years, they concluded, the virus has evolved so that it thrives much better in domestic fowl.

Thai Prime Minister Thaksin Shinawatra this week blamed wild open-billed storks for the current outbreak. Chaturon, however, said the storks would not be indiscriminately killed.

“Random checks found the virus in some storks, but we will not seek to kill them en masse,” he said. “We will only cull the ones that are found with the virus and dispose of the dead birds properly.”

Robert G. Webster of St. Jude Children’s Research Hospital in Memphis, Tenn., has studied samples of the virus collected each year since 1998 and reported last week in the Proceedings of the National Academy of Sciences that the viruses collected most recently could infect mice more easily and were deadlier than those collected earlier. That suggests that the virus is accumulating mutations that will allow it to infect humans more readily, he said.

Currently, the virus appears to be a threat only to people who come in direct contact with infected birds or their feces. The virus has not been shown to be transmitted from person to person.