Gene study suggests China source of H5N1 virus

WASHINGTON (Reuters) - Southern China may have been the source for much of the spread of the H5N1 avian flu virus, researchers suggested on Tuesday.

A genetic analysis of the virus shows that strains that showed up in Vietnam, Thailand and Malaysia in 2002 and 2003 closely resemble a strain from poultry markets in China's Yunnan Province, the flu experts found.

Two viruses found in poultry in China's Hunan province in 2002 and 2003 were most closely related to viruses from Indonesia, they reported in the Journal of Virology.

"These results suggest a direct transmission link for H5N1 viruses between Yunnan and Vietnam and also between Hunan and Indonesia during 2002 and 2003," wrote the researchers, who included Guan Yi of the University of Hong Kong and Robert Webster of St. Jude Children's Research Hospital in Memphis, Tennessee.

"Poultry trade may be responsible for virus introduction to Vietnam, while the transmission route from Hunan to Indonesia remains unclear," they wrote.

The H5N1 bird flu virus was first seen in a goose in southern China's Guangdong province in 1996. A 1997 outbreak in Hong Kong killed six people.

The virus reemerged in 2003 when two members of a Hong Kong family who had recently visited Fujian province became ill and one died.

Since 2003, H5N1 bird flu has been found in more than 60 countries and territories. It has killed 236 people out of 373 infected in 14 countries -- Myanmar, Turkey, Djibouti, Azerbaijan, Egypt, Pakistan, Iraq, Indonesia, Thailand, Vietnam, China, Nigeria, Laos and Cambodia.

Bird flu now almost exclusively infects birds. But it can occasionally pass to a person.