DHAKA, Feb 10 (Reuters) - Bird flu has spread to another district in Bangladesh despite efforts by authorities to contain it, taking the number of affected districts to 40, officials said on Sunday.

Health workers culled nearly 12,000 fowls after tests confirmed some chickens had died from the avian influenza virus in the northeast, livestock officials said.

The H5N1 virus, first detected in Bangladesh in March last year, was quickly brought under control through aggressive measures, including culling. But follow-up monitoring eased in later months prompting the disease to reappear, experts say.

So far, no human infections have been reported in Bangladesh, a densely populated nation with millions of backyard poultry and thousands of chicken farms.

The interim government has enhanced compensation for poultry farmers to encourage them to report and kill sick birds.

More than half a million birds to be culled across the country, but the virus has spread to more than half the South Asian country's 64 districts partly due to a lack of awareness.

Media reports said many children were seen smiling and playing with dead poultry.Even health workers have been seen burying dead birds without any protective gear.

The World Health Organization worries that the H5N1 strain, which has already killed more than 220 people worldwide since 2003, could mutate into a form that passes easily between humans and infect and kill millions. (Reporting by Ruma Paul; Editing by Bill Tarrant)

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