DHAKA, Sept 27 (Reuters) - Bangladesh culled some 5,000 chickens after bird flu infected a farm in the northern region of the country, officials said on Thursday.

"The chickens were buried on Wednesday after H5N1 virus was detected at a farm near Bogra district town 250 km (150 miles) (156 miles) north of the capital Dhaka," an official of the livestocks department said.

Bird flu was first detected near the capital in March and has since spread mostly to northern districts.

Eighteen out of Bangladesh"e;s 64 districts have been affected by the virus since March, but there have been no cases of human infection. The virus has forced authorities to cull 262,000 chickens.