(Agencies)
Updated: 2008-01-27 21:20

BEIJING -- Authorities in western China lifted a bird flu quarantine Sunday after no new outbreaks were reported.

No cases of human infection were reported in Northwest China's Xinjiang Autonomous Region outbreak of the deadly H5N1 bird flu virus strain, the Agriculture Ministry reported, according to the Xinhua News Agency.

The lifting of the quarantine came 21 days after some 35,000 birds were ordered slaughtered to prevent the virus from spreading, Xinhua said. Farms in the area have been disinfected, and workers who came into contact with sick birds showed no sign of infection, it said.

China has vowed to aggressively fight the H5N1 virus, which has killed at least 221 people worldwide, according to the World Health Organization.

The virus remains hard for humans to catch, but experts worry that every outbreak in poultry may make it easier for the virus to mutate into a form that passes easily among people, potentially igniting a flu pandemic. Most human cases have been traced to contact with infected birds.

Last week, authorities confirmed that a father and son who were sickened with bird flu were the country's first infections within the same family, but said their cases showed no evidence that the virus has changed into a form that can easily be passed between humans.

The 24-year-old son from the eastern city of Nanjing died December 2, becoming China's 17th fatality from the virus.