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PHNOM PENH, April 6 (Reuters) - A 13-year-old Cambodian girl has died of bird flu, bringing the country's death toll from the H5N1 virus to seven since 2003, the World Health Organization and the government said on Friday in a joint statement.

"Samples from the girl tested positive for the influenza H5N1 virus at the Pasteur Institute of Cambodia in Phnom Penh," said the statement.

The girl, from the eastern province of Kampong Cham bordering Vietnam, fell ill with fever and diarrhoea on Monday after preparing and eating a sick chicken at home, the statement said.

She was taken to a hospital in Phnom Penh where she died on Thursday, it said.

Agricultural officials were sent to test poultry in the area, where chickens were dying before the girl fell ill. Local health and WHO officials were visiting the area to check if there were any more people who had fallen ill.

The virus, which has killed 170 people since 2003, according to the WHO, has not shown the ability to mutate into a form that could pass easily between humans, causing a pandemic that might kill millions of people.

But experts fear it might, especially in a poor country like Cambodia, which is recovering from 30 years of civil war and where health surveillance systems are rudimentary at best.

Neighbouring Thailand, Vietnam and Laos have also had bird flu outbreaks this year.

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