It has been just over a month since WB authorities claimed bird flu had been contained in the state. They are now, however, reporting that avian influenza has resurfaced in West Bengal's Darjeeling district.
Culling operations in West Bengal to contain the third outbreak had ended barely a month ago.
The epicentre has been detected as Bora Changa in the same region.
West Bengal officials said they had begun culling about 11,000 poultry after the fourth outbreak was confirmed on Sunday near Siliguri town.
"We have started culling operation on the basis of notification made by the Government. Bora-Changa epicentre was declared again affected and accordingly we have started our operation. We hope so it will be completed in the next three to four days," said Dhruba Chakrabarty, state observer, animal husbandry division.
Samples of blood have been sent to High Security Animal Disease Laboratory in Bhopal.
Earlier in January, bird flu outbreaks were reported in Siliguri and adjacent areas and more than 30,000 birds were culled.
Buying and selling of chicken have been banned within 10 kilometre of the affected area to avoid further spread of the disease.
Hundreds of thousands of birds had been culled in Assam and Meghalaya after bird flu was detected in November.
Bird flu first broke out in India in 2006. Millions of chicken and ducks have been culled since to contain the virus.