Chennai: Is thermal fogging an effective tool to control mosquito menace in the city? No, say experts and officials of the Greater Chennai Corporation.
What is troubling here about its usage is that it is excessive - the corporation maintains that they fog everyday in all 15 zones - and that contributes immensely to atmospheric pollution.
Fogging involves spraying contact poison in the air. Micro granules in the fog attack the nervous system of the adult mosquito, injects neurotoxins through its trachea, which leads to paralysis and then death of the adult.
But the process requires copious amounts of diesel fuel, which carries the insecticide. Fog sprayed by the machine consists of 19 parts diesel to one part mixture of malathion and pyrethrum, the insecticides used to kill the mosquito.
Officials said that a hand-held fogging machine is capable of consuming over five litres of diesel in under an hour. Vehicle-mounted foggers need more than 50 litres per hour. “The machines themselves need petrol to operate,” said an official.
Public health department officials observed that there was complete lack of application when it came to choosing the time to fog. “I have seen vehicle mounted machines fog during the day, when the humidity is less. What happens is that the fog escapes into the air the moment it is out of the machine,” said a senior public health official.
Former Chief Vector Control Officer of the corporation B. Dhanraj recollected an incident when a group of entomologists from Sri Lanka on a field visit to Chennai during his tenure, discovered the ‘generous’ fogging activity in the city. “They were shocked because even WHO prescribes fogging only during an [epidemic] outbreak,” he said.
Dhanraj calls thermal fogging as “one of the best cosmetic affairs” but he also blames the public mindset for the situation. “Everyone thinks that fogging helps reduce mosquitoes. Even when they complain about mosquito menace, residents insist that the corporation has not been fogging their locality,” he added.
Given this situation, the vector control department has had to continue fogging under pressure from higher officials, who act on the mandate of politicians. “Imagine what the public would think of an administration that did not fog to control mosquitoes,” Dhanraj said.
As another public health official noted, if the corporation was successful in curbing breeding sources, there would be “no need to repeat the breeding control procedure every month of every year.”
“If only a fraction of money spent on fogging is invested in breeding source control programme, Chennaiites will heave a sigh of relief and the environment can be saved as well,” a senior corporation official noted.
