The rain over the past two days has created conditions ideal for mosquitoes to breed and triggered fears of a renewed spurt of dengue.

“We have asked our field-level vector control workers to visit each and every house.... We have also asked them to conduct awareness campaign and announce the dos and don’ts through microphones in lanes and bylanes,” a Calcutta Municipal Corporation official said.

Calcutta, as well as the rest of Bengal, has witnessed a steep jump in the number of dengue cases over the past month, a senior health department official said.

The CMC official said about 2,500 cases had been reported since January, 1,700 of them over the past month. The vulnerable places in Calcutta include Behala, Parnasree, Golf Green, Bijoygarh, Alipore, Tangra, Tollygunge Ashoknagar and Jadavpur.

After every spell of rain, small containers such as clay or plastic cups get filled with water. If the containers remain undisturbed and away from sunlight, they could turn into mosquito breeding sites.

“The Aedes aegypti mosquito, which transmits the dengue virus, can breed in a spoonful of water. It takes a week after eggs are laid for adult mosquitoes to emerge. So, it is crucial to drain out stagnant water once in seven days,” said an entomologist.