DHAKA, Dec 1 (Reuters) - Bird flu has spread to another district in northwestern Bangladesh, forcing health and veterinary workers to cull some 6,000 chickens and destroy over 2,500 eggs, officials said on Saturday.

The latest case was reported in a village in Pabna district, 160 km (100 miles) from the capital, Dhaka, a senior official of the fisheries and livestock ministry said.

Bird flu was first detected near the capital in March and has since spread mostly to northern districts. There have been no cases of human infection.

Including Pabna, 20 of Bangladesh"e;s 64 districts have been affected by the virus, which has forced authorities to kill 256,000 chickens and destroy nearly three million eggs since its outbreak.

About 4 million Bangladeshis are directly or indirectly associated with poultry farming. (Reporting by Ruma Paul; Editing by Michael Winfrey)