The drizzle on Tuesday and the consequent drop in temperature have created conditions suitable for the spread of dengue and other viral diseases, public health professionals warned.

The light rain has created puddles, which are ideal for the dengue carrier, the Aedes aegypti mosquito, to breed.

That apart, fluctuating temperatures can lead to infections in the upper respiratory tract and a rise in the incidence of viral diseases.

“Tuesday’s rain will create water pockets that could turn into breeding sites of the Aedes aegypti mosquito. Containers that remain hidden under garbage, where sunlight does not reach, are ideal breeding sites of these mosquitoes,” said Debashis Biswas, the chief vector control officer of the Calcutta Municipal Corporation (CMC).

“Since sunlight does not reach such hidden pockets, the water does not dry up naturally.... It takes seven days for an adult mosquito to emerge from an egg. That is why people are advised to drain out stagnant water at least once a week,” Biswas said.

Doctors warned that the variation in temperature because of the cloud cover and rain — the maximum temperature plummeted from 27.1 degrees on Monday to 22.6 on Tuesday — could lead to a spurt in viral infections.

Physician Amitabha Saha said the temperature variation helped viruses to replicate faster. “There could be a rise in viral infections since the temperature variation helps viruses to replicate faster,” Saha said. The defence mechanism of humans does not work well during such periods of temperature fluctuations, which is another reason for a likely spurt in viral diseases.

A CMC official said the civic health department had alerted its field workers to ensure all mosquito breeding grounds were destroyed. “The workers have also been asked to go on a door-to-door campaign,” the official said.