Breeding data can help tackle Chennai’s mosquito menace

In August, the Greater Chennai Corporation received 1,134 complaints of mosquito menace – a problem that has been persistently bothering the city’s residents and challenging the civic body. 

The shabby state of the city’s waterways and illegal sewer connections to stormwater drains are primary causes behind the explosion in mosquito menace. However, aiming to understand the breeding patterns, the Corporation has plans to set up a Vector Command and Control Centre, which has already piloted a programme to track the larval growth cycle in the waterways through an app, which can help contain the mosquito menace.

Jayashree S, a resident of CIT Colony in Nandanam, has been bearing the brunt of official callousness every evening when mosquitoes swarm the locality. 

“We have put nets on all our windows but after sunset, the mosquito menace is unbearable. There have been a lot of fumigations carried out by the Corporation, but it has had little impact. In fact, we have been lodging regular complaints with the zonal-level Corporation offices but nothing much has changed. It looks like the mosquitoes have become resistant to fumigation and residents continue to suffer,” said the retired professional. 

The major breeding spots for mosquitoes are the city’s waterways blocked by water hyacinth and polluted by solid waste, and the stormwater drain network, out of which 50 per cent of the drains have water stagnation due to missing links and illegal sewer connections. The Corporation maintains 1,894 kilometres of stormwater drain network and 30 canals across the city.

“Chennai has 234 kilometres of waterways, in addition to the storm water drain network. Almost 40-50 per cent of storm water drains will have stagnation due to the sewage inflow through illegal connections. A weekly schedule has been drawn up to spray larvicide in these drains to control breeding of the mosquitoes. In addition, we have 34 vehicle fumigators and 238 portable fumigators. If there is an identified case of dengue, door-to-door fogging is carried out in that locality,” said an official from the Corporation’s Vector Control Department.

In addition, the department has also employed personnel to check breeding in the city’s households. The 17 lakh households in the city have been divided into 2,035 sectors. “Each sector is managed by one person, who will go to the houses and check for mosquito breeding activity in the freshwater sources – such as water stored in plastic bins, for example. The malaria-causing Anopheles mosquito and the dengue-causing Aedes mosquito breeds in fresh water sources, often found in stagnated fresh water in households,” said the official.

Most of the water bodies and inter-linking canals in the city are choked by water hyacinth and solid waste, mostly plastic and other non-biodegradable trash. In addition, the sewage inflow into our rivers makes it the perfect breeding ground for mosquitoes. Seven of the city’s 15 zones have rivers meandering through the localities. Cooum river, which starts at Valsaravakkam (zone 11), goes through Anna Nagar (zone 8) and Teynampet (zone 9) before entering the sea, through Royapuram (zone 5). Adyar river starts at Alandur (zone 12), going through Kodambakkam (zone 10) and Adyar (zone 13) before draining into the sea. The Buckingham Canal, too, criss-crosses across various zones of the city.

While a bio-larvicide with bacillus thuringiensis is being used in the waterways to check larvae breeding, there is no clear understanding of the breeding patterns due to lack of historic data. To understand this, the Corporation will soon be piloting a project to understand the larvae breeding information.

Despite the serious challenge faced by the civic authorities and public health officials, a vector control monitoring system project to check the live breeding spots along the city’s waterways has been in the cans for more than a year now. However, sources in the Corporation reveal that a pilot will soon be conducted to ascertain the feasibility of such a centre.

“Along the course of the waterways, existing breeding spots will be identified and assigned a number. Field workers will be given an app to capture the larval presence in these spots, which will be relayed to the control centre here at Ripon Building [headquarters of the Corporation]. The app will capture data such as the coordinates of the spot, humidity, minimum and maximum mean temperatures, and larval presence. This will help us understand the breeding patterns in the waterways, to begin with, and subsequently, implement larval-control measures effectively. Once this is implemented, we will have a better understanding of the breeding activity and significantly reduce mosquito menace in the city,” said the official.

Until this system is implemented, the Vector Control Department’s activities are limited to routine measures like fogging and guesstimated anti-larval measures – though they have had little impact on the overall situation.

The major requirement, according to officials from the department, is the regular desilting of stormwater drains and waterbodies. “Though we have three robotic excavators and one amphibian machine, it is insufficient to clear out the city’s waterways. All we can do is continue with the existing system,” added the official.