Scientists have discovered a new strain of bird flu that has infected humans in China, which could arouse fresh fears of a possible pandemic and spur further interest in experimental drugs and vaccines.

Dr. Robert Webster of St. Jude's Children's Research Hospital in Memphis, along with other scientists from the U.S. and China, announced "the emergence and pre-dominance of a previously uncharacterized" substrain of bird flu, appearing in Chinese poultry since late 2005.

The scientists, who published their findings on the Proceedings of the National Academy of Sciences Web site, also reported that the substrain of H5N1, also known as bird flu, had "caused recent human infection in China." Researchers noted that some of these cases were residents of urban areas remote from poultry farms.

"The development of highly pathogenic avian H5N1 influenza viruses in poultry in Eurasia accompanied with the increase in human infection in 2006 suggests that the virus has not been effectively contained and that the pandemic threat persists," the researchers concluded.

Bird flu typically emerges in poultry and wild birds, but the often fatal virus can be spread to humans who are in close contact with the infected birds. The virus emerged in Asia in 2003, and to date it has infected 256 humans and killed 151, with Vietnam and Indonesia accounting for the majority of cases, according to the World Health Organization. But there have been only limited incidents of human-to-human transmission, with nothing sustainable. Human-to-human transmission is the greatest fear of health workers around the world because strong cases of human-to-human transmission have the potential to spark a global pandemic, like the strain of influenza that killed tens of millions in 1918. The U.S. Department of Health and Human Services (HHS) has estimated that a pandemic outbreak in the U.S. could kill up to 300,000 people.

And with more than 50 known strains of H5N1, the discovery of a new one doesn't necessarily mean the end is nigh, experts point out. "I don't consider it that worrisome yet," said Ren Benjamin, biotech analyst for Rodman & Renshaw. "Once it mutates or becomes more pathogenic, then it becomes something to worry about. If you make the discovery that there's human-to-human [transmission,] then the red flag will go up."

Source:佚名