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送交者: mangolasi 于 2005-12-09, 08:15:44:

Scientist Says Bird-Flu Virus
Is Currently Stable in China
December 9, 2005 8:23 a.m.
BEIJING -- Although human cases of bird flu are mounting in China, the virus here is currently stable, not mutating toward a form readily transmissible among humans, a top Chinese government scientist said.

Shu Yue Long, director of China's national influenza laboratory in Beijing, also said that amantadine -- a drug that was largely discredited when the virus was thought to have grown resistant to it -- may be effective in treating avian influenza in people after all, though that evidence is still preliminary.

China's Xinhua news agency reported on Thursday that a farmer in northeastern China had tested positive for the H5N1 strain of bird flu, making her China's fifth confirmed human case of the disease. Until mid-November, China had said it was free of human cases.

Global health authorities seeking to stave off a bird-flu pandemic have been monitoring human infections with particular interest. So far, the virus has mainly affected poultry, with only about 70 confirmed human fatalities in five Asian countries since late 2003. But authorities fear the bird-flu virus could mix with a normal strain of human influenza, swapping chunks of genetic code and spawning a deadly virus that could pass from person to person with the ease of the common cold.
Dr. Shu said that the virus in China appears to be stable rather than mutating in this way. That jibes with the findings of the World Health Organization in Geneva, which has seen no evidence so far that the bird-flu virus has evolved to spread easily from person to person anywhere in Asia.

Birds and humans have different kinds of receptor proteins on the surfaces of their lungs' epithelial cells. Currently, the hemagglutinin protein on the surface of the H5N1 virus binds easily to bird cells but not to human cells. That allows the virus to burrow into the avian cells and replicate, accounting for the vast numbers of infected birds around the world.

Although H5N1 has only recently been reported in humans in China, and such a mutation could still occur, Dr. Shu said that in viruses isolated from the few human cases in China, there have so far been no such significant changes in the protein.

Also encouraging is the possibility that the antiviral drug amantadine may be more effective at combating bird flu in humans than scientists believed. Amantadine is far more widely available and less expensive than oseltamivir, marketed as Tamiflu by the Swiss drug company Roche Holding AG. Governments around the world have been scrambling to stockpile Roche's Tamiflu as a hedge against a pandemic.

All of the samples of the virus that have been isolated from patients in China would be sensitive to amantadine, Dr. Shu said. Those findings dovetail with research on virus samples that have been taken from patients in Indonesia and also show sensitivity to the drug, according to Hariadi Wibisono, director of vector-borne disease control for the Indonesian Ministry of Health in Jakarta.

Those early results have prompted officials in Beijing and Jakarta, as well as officials of the World Health Organization in Geneva, to consider whether amantadine may eventually play a role in fighting the disease. Right now, however, there are too few samples to draw any firm conclusions.

"If we tested a hundred isolates, and most of them were sensitive, we might recommend amantadine and oseltamivir to treat human cases of avian influenza," says Dr. Shu.

Another Outbreak in Japan

H5 bird-flu antibodies were detected Friday at a chicken farm in northern Japan, Kyodo News agency reported. It wasn't immediately clear whether the antibodies, found in birds at a farm in Ibaraki prefecture, north of Tokyo, were the H5N1 strain. Antibodies indicate that birds contracted bird flu, but recovered.

Japanese authorities have culled millions of birds since bird flu hit Japan last year for the first time in decades. Most of the outbreaks have been in Ibaraki, and have involved the H5N1 strain.



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