A 20-year-old Cambodian woman who died in Vietnam this week was killed by bird flu, taking the death toll in Asia to 52, a health official said on Friday.

The woman died just hours after being rushed to hospital on Tuesday in Vietnam’s southern province of Kien Giang, suffering from high fever and respiratory problems, a doctor who treated the woman told Reuters.

“This case has tested positive,” said a Ho Chi Minh City official, who declined to be identified, following tests on samples from the woman at the city’s Pasteur Institute.

Four Cambodians have now died of bird flu, all of them from Kampot province, which borders Vietnam. The H5N1 virus has also killed 36 Vietnamese and 12 Thais.

Health experts fear the virus could mutate into a form that can pass easily between humans and millions could die in a global pandemic and cases in places like Cambodia, where health and monitoring systems are rudimentary, only sharpen the fears.

The virus is endemic in several areas of Southeast Asia and Vietnam, the country hardest hit, says it does not expect to be able to contain it until next year or 2007 because the way it spreads still baffles experts.