DHAKA, Feb 15 (Reuters) - Bird flu has spread to another district in Bangladesh despite massive culling by authorities to contain the outbreak, officials said on Friday, bringing the number of affected districts to 42 out of 64.

Veterinary workers culled nearly 25,000 fowls after tests confirmed some chickens had died from the avian influenza virus in Comilla, in the south east, 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 it reappeared few months ago, apparently because of lax follow-up monitoring, experts say. Officials said the government was taking measures to contain the spread of the disease, but ignorance among millions of farmers across the impoverished country remained a stumbling block.

The government has raised compensation for poultry farmers to encourage them to report and kill sick birds as part of efforts to stamp out the outbreak.

More than 600,000 birds have been culled across the country against the virus since March 2007, but it continues to spread and now covers nearly two-thirds of the country of more than 140 million people.

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

Experts fear the H5N1 strain could mutate or combine with the highly contagious seasonal influenza virus and spark a pandemic, especially in countries such as Bangladesh where people live in close proximity to backyard poultry.

Humans usually contract the virus only after close contact with infected birds, with the virus killing nearly two-thirds of the people it infects. The disease has killed more than 220 people worldwide since 2003. (Reporting by Ruma Paul; Editing by Alex Richardson)

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