It is the time of the year when Chennai’s weather swings rapidly between sultry heat and short, sudden spells of showers. With the North East monsoon nearly two months away, these short-lived bursts of rain signal the onset of another phenomenon: the onslaught of mosquitoes.
To prevent the spread of vector-borne diseases like dengue and malaria, the Chennai Corporation usually makes arrangements to spray larvicide along Chennai’s three main water bodies – the Adyar river, the Cooum river and the Buckingham canal, which are arguably the city’s largest mosquito-breeding grounds. Boats are usually taken out to reach parts of these water bodies inaccessible by land.
But this year, tackling the mosquito menace has become much harder. The eight boats that the Chennai Corporation has been using for this purpose were wrecked and rendered unusable after last year’s floods, reported The Times of India. Eight months after the floods, these boats have not been replaced either.
Mosquito menace
B Dhanraj, a former Chief Vector Control officer of the Chennai Corporation, said that boats were essential to access mosquito breeding grounds that are usually located among weeds along either side of the waterways. “One cannot go and spray the edges there,” he said. “Accessibility is a problem in many places as houses have been built along the river. If you don’t spray even for a stretch of 100 metres because of inaccessibility, you are supporting breeding of mosquitoes.”
But wrecked boats are not the only problem here. The growth of water hyacinth – the natural home of the culex mosquito, which can transmit Japanese encephalitis and lymphatic filariasis – has reportedly doubled after the floods too.
Dhanraj said that during the floods, garbage and sewage would have mixed with rainwater and flowed into the rivers, increasing the nutrient content in these water bodies. This, he said, created a rich environment for the growth of water hyacinth.
Thus, with no boats and the possibility of an increase in mosquitoes this season, the city is likely to see a spurt in mosquito-borne diseases.
Engineering solution
The city could better tackle the mosquito menace if it enabled these waterways to flow, suggested Dhanraj.
At present, the water bodies – much like the Mithi river in Mumbai and the Hindon in Delhi – are mainly stagnant, still or slow-moving drains that only flow when it rains heavily. Insect larvae grow in still water. Thus, if the velocity of the waterways were to increase, mosquitoes would not be able to breed in these areas.
According to Dhanraj, one good way of getting them to flow was by desilting the mouth of the rivers. If this is done, the entry of saline water from the sea inland up to a few kilometres would prevent mosquitoes from breeding.
Breeding in homes
But large water bodies are not the only places where mosquitoes breed, said S Elango, former director of public health.
Mosquitoes belonging to the anopheles and aedes groups, which transmit malaria and dengue, breed in rainwater collected in overhead tanks, garden pots, vases and discarded junk with the smallest of puddles in them.
Elango said that the attitude of citizens did not help, and the mosquito menace could only be tackled if citizens cooperated.
“In Chennai, wherever you go, be it urban slums or behind bungalows and villas, there is all sorts of waste dumped there," he said. "There is no adequate human resource to remove this. People do not have any civic sense. They dump waste and expect that everything will be removed by the corporation staff."
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