DHAKA (Reuters) - Health and veterinary workers inBangladesh have culled nearly 25,000 fowls after bird flu wasconfirmed at three poultry farms in the country, officials saidon Thursday.

Bird flu has spread to the southern coastal district ofBorguna and the northwestern Rajshahi district, a livestockministry official said. Another infection was reported inJessore, 275 km (170 miles) from the capital Dhaka.

"After the confirmation of bird flu, authorities have begunculling at the affected farms and surrounding areas," theofficial said. "So far nearly 25,000 chickens, ducks andpigeons have been culled in three districts."

Fowl were also culled in the southern coastal district ofBarisal after detection of the H5N1 avian influenza virus.

Suspected outbreaks were also reported at a farm innorthern Rangpur district, where the virus has been confirmedin fowl previously.

The H5N1 virus was first reported near the capital in Marchlast year and has since spread to 25 of Bangladesh's 64districts, forcing authorities to kill more than 300,000chickens.

So far there have been no cases of human infection in thedensely populated country, government officials say.

But experts fear the bird flu virus might mutate or combinewith the highly contagious seasonal influenza virus and spark apandemic that could kill millions of people.

There have been 217 human deaths globally from the H5N1strain and 350 confirmed cases of infection since 2003, WorldHealth Organisation figures show.

In neighboring India, veterinary workers began killingthousands of chickens in West Bengal state on Wednesdayfollowing what the WHO said was the worst outbreak of bird fluin the country.

Officials said it could take up to a week to cull about350,000 birds in three districts of West Bengal.

(Reporting by Ruma Paul; Editing by Jeremy Laurence)