DHAKA, June 24 (Reuters) - Health workers in Bangladesh have culled 78,000 chickens over the past six days after bird flu spread to another district in the north of the country, an official said on Sunday.

The H5N1 strain of bird flu was first detected near the capital Dhaka, in central Bangladesh, in March and has since spread to north.districts.

The latest outbreak was reported from three farms in Lalmonirhat district, 400 km (250 miles) northwest of Dhaka, an official said.

"We have culled a huge number of chickens after the virus spread to the new district," said Khalilur Rahman Siddiqui, joint secretary, ministry of fisheries and livestock.

With the latest cull, about 250,000 chickens have now been slaughtered and more than 2.2 million eggs destroyed in 15 districts since March.

There have been no reported cases of human infection.

About four million Bangladeshis are directly or indirectly associated with poultry farming.

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