Ways to control breeding of mosquitoes in Chennai

‘Mosquitoes are engineering problem; malaria, dengue are medical problem’

March 08, 2023 05:38 pm | Updated 05:38 pm IST

Image for representation purpose only.

Image for representation purpose only. | Photo Credit: AP

As the Corporation’s City Health Officer in Chennai from 2006 to 2014, I was in charge of handling mosquito control activities in the city. At that time, the major complaint of the members of the public was the mosquito menace — the issue came up repeatedly in the Corporation Council, grievance meetings and via petitions to the civic body.  

It is common knowledge that 50% of mosquitoes breed in rivers and canals, another 40% in stormwater drains and about 10% breed in individual houses. These mosquitoes that breed in domestic settings are responsible for causing malaria and dengue, and therefore, control requires people’s participation to be successful. At that point in time, it was very difficult and hence we wanted to make it people’s movement in order to get it to work. 

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Among the perennial sources of mosquito breeding in the city are the waterways like Cooum, and Adayar rivers, and canals like Buckingham, Otteri Nallah, and Virugambakkam Canal, all running for about 247 kilometres. The other source is the stormwater drains flowing under the streets of Chennai City for nearly 2,100 kms, and side drains for about 412 kms. They are the water sources that allow the breeding of what we call nuisance mosquitoes throughout the year based on the amount of water stagnation. These are culex mosquitoes, and they do not cause malaria or dengue but sometimes filariasis. 

The stormwater drains in the city have over have about 3 lakh illegal connections of sewers either intentionally damaged by people, or accidental breakage during the construction of stormwater drains. The non-flowing sewer water stagnates throughout the year.  

My engineer friends would always be annoyed at me during the Commissioners’ review on Saturdays when I used to list out the length of SWD having stagnation — and thus homes for breeding mosquitoes. The stormwater drains which are supposed to be dry during summer were 60% filled with sewage. They are constructed only for floods in rain not for sewers. They have no interconnections to drain out of the city as they were not scientifically designed for this purpose. Moreover like Mumbai, Chennai is located equal to or lower than sea level, hence drainage is difficult. 

The solution for this could be like in Japan we need to install deep charging bores or wells in many parts of the city which will not only reduce flooding but raise the ground level water. They could also fill the temple tanks and lakes in and around the city providing connecting pipelines from the places of heavy water stagnations. 

The true issue that bothered the health officials was the breeding of the other types of mosquitoes — those that breed in clear water only — anopheles and aedes — causing malaria and dengue. 

Dry day in a week 

The domestic sources of mosquito breeding are household open overhead tanks, open wells, open sumps, temple tanks, lakes and septic tanks beside household storage of water during water scarcity. 

Temporary sources of breeding at each house include old tyres, used disposables like tea cups, tins, coconut shells, unused grinding stones, broken toilet wares (when water collects in them), stagnant water on uneven terrace, tree leaves clogging in the pipe lines and shades etc. 

We decided to organise Dry Days for the OHTs once a week in the housing colonies, in order to take the message of domestic breeding of mosquitoes and the way to prevent them to the public.  

Rivers and canals

We would get alerts about increasing mosquito nuisance from MLA Quarters near the Cooum and Ministers Quarters near Adyar river. Immediately the PWD department used to be requested to dredge the daily accumulating sand bar at the mouth of these rivers on daily basis till the complaints stop. 

The corporation usually spends nearly ₹10 crore every year to spray insecticides, (malaria larvicide oils from oil companies) in these waterways, especially on the edges and the banks of canals which usually have wild bushy vegetation; nearly 20 fibre boats and catamarans with fishermen were used for spraying insecticides and removal of large plastic waste in these rivers. 

The water coming from the outskirts of Chennai usually brings in new larvae to the city and hence I had instructed our staff to erect larvae filtering nets across water ways. This turned out to be very useful.  

We realised that it is the defective engineering measures which are the causative factors for mosquito breeding in the city. In fact, we gave a proposal to the PWD to develop a permanent structure to install angled pipelines across the mouth of rivers in the opposite direction of sea waves to ensure the free flow of seawater into the rivers without sand bar formation. Its effective implementation at the river mouth could not only reduce the cost of mosquito control to the minimum but greatly reduce the mosquito density and permanent relief for Chennaites from mosquito nuisance. 

The recommendations were technically made and supported by Oceanographic Engineers of IIT, Madras (Prof. Dr. Mani). I want to clarify that contrary to common belief, seawater doesn’t affect the groundwater. In fact, it was done during the British rule with mechanical lockers near the mouths to hold and balance sea water in the canals and rivers for transport and to stop mosquito breeding with saline infusion. 

We gave a proposal in 2010 to buy a Norway-made and popularly used amphibian vehicle costing ₹1 crore to dredge mud and trim the edges of the waterways to allow the free flow of water, and it was later purchased. Its effective daily utility with the dredging of sand at the river mouth would not only reduce the cost of mosquito control to the minimum but greatly reduce the mosquito density and nuisance. 

Regulatory punitive actions

Closing of the OHTs and wells which was technically called “Hermetical sealing and Scientific closure of wells and OHT” was mandated by issuing a notice under TNPHACT 1939, SEC 83,84 and entailed prosecution in the court of law for noncompliance. 

The illegal sewer connections to the stormwater drains were not allowed under Sec 17 to 36 of TNPH ACT 1939. Notices were issued and those in charge of construction sites where water was allowed to stagnate were punished. 

“Mosquitoes are engineering problem; malaria, dengue are medical problem” 

Developed nations as well as the WHO have repeatedly instructed that the breeding of mosquitoes continues to be an engineering problem, and only treatment of malaria and dengue is the health problem. But in our set-up, both mosquito and malaria control is being undertaken by the health department, arguably not the most scientific way of handling the problem.  

School Health Ambassador 

Another tool that was used effectively in the control of domestic mosquito breeding (with the support of the public) is school students.  

Nearly 5 lakh students were involved, sensitised on this issue and named as Health Ambassadors, and were also given an ID card.  

They were motivated to teach their family and neighbours about breeding zones in their homes, leading to an increasing mosquito population, causing disease as well. Some schools gave them assignments; they were shown the live mosquitoes in the prayer meeting and exhibitions were conducted to identify the issues and types of mosquitoes.

After a 3-week, sustained drive, the adult mosquito/larval density had come down to the minimum thereby reducing the nuisance and the occurrence of diseases. 

Sector control approach

During the dengue epidemic in 2011, when alarming deaths were witnessed at the national level, Chennai city recorded less than 300 cases; I instructed my team not to rely on fogging (diesel mixed synthetic pyrethroid which is expected to knock down mosquitoes by neural poisoning) and spraying alone, but rather on 100% reduction of breeding sources in the individual houses. 

There were about 17.5 lakh households in the city then; my team was instructed to inspect 100 houses/day, 500 houses /week thoroughly by field staffers, to remove the breeding sources, especially tyres and put them on the streets for removal by the conservancy and to give them awareness about mosquitoes and the diseases they spread.

These 500 houses were considered a cluster and called a sector. 3,500 workers were deployed on a contract basis after short training. In fact, we were surprised that just this simple measure reduced the larva/mosquito density when each area was measured by entomologists for man hour density later. 

It is high time that public health experts and administrators in the State, technically and rationally revised the current vector control program which suffers from inadequate manpower, machinery, and tools. It would be advised to drop our old conventional methods in favour of new, modern and updated vector control research and implementation. 

Setting right basic engineering flaws, even as we envisage new plans for Singara Chennai 2.0 and right engineering decisions as a part of essential town planning activity will be beneficial for the city. That is the only thing that can, in a more permanent and concrete way, ensure that our waterways remain free from breeding mosquitoes. 

(Dr. P. Kuganantham was the former health officer of the Chennai Corporation. He can be reached at drkugan@yahoo.com)  

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