(Corrects headline and last paragraph to boy from teenager)

HANOI, March 17 (Reuters) - Bird flu has killed a 11-year-old boy in northern Vietnam, the fifth casualty from the H5N1 virus this year, a health official said on Monday.

The boy died last Friday at a Hanoi hospital, more than a week after he had fallen sick, and tests confirmed he was infected by the H5N1 virus, said Nguyen Lap Quyet, Health Department Director in Ha Nam province.

"Controlling bird flu has been difficult because poultry raising is not on a large scale but still on a family basis," Quyet said by telephone from Ha Nam, about 60 km (37 miles) south of Hanoi.

He said animal health workers have slaughtered all the poultry in the boy's neighbourhood to prevent the virus from spreading.

"Even after vaccination has been completed locally, farmers buy poultry to add to their stocks and that could help spread the virus if the new birds are not vaccinated," he said.

Chickens raised at the boy's house in Liem Tiet commune in Ha Nam died in late February and he got sick on March 5.

The Animal Health Department said on Monday that Ha Nam was on the government's bird flu watch list of 10 provinces and the capital, Hanoi.

In June 2007 bird flu infected and killed a 28-year-old woman in the same commune of Liem Tiet in Ha Nam province.

Five people have died of bird flu in Vietnam so far this year out of six reported H5N1 infections.

The World Health Organisation has not confirmed the death of the boy. The WHO said bird flu has killed 235 people among 372 known cases globally, among them 51 deaths in Vietnam. (Reporting by Ho Binh Minh, editing by Grant McCool and Sanjeev Miglani) (Also see TAKE A LOOK-The threat from Bird Flu)

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