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Control Of Mosquitoes And Mosquito Borne Diseases:

  • Chennai City is encountering twin problem of mosquito menace and mosquito borne diseases like malaria, dengue and filariasis.
  • Between these two public health issues, the problem of mosquito menace is realized more by the people of Chennai than the diseases.
  • The chief sources for mosquito menace in Chennai are waterways and storm water drains.

Water Ways:

There are three major waterways and sixteen minor or arterial drains. These are meant to carry away rainwater. As of now all these waterways are carrying sewage and are acting as ideal breeding source for Culex quinquefasciatus mosquitoes, which are also called as Pest mosquitoes. The sewage from CMWS&SB pumping stations is let into these waterways at several places in the city. It is estimated that 85% of the pollution in these water ways is caused by the CMWS&SB and 10% from the industries and 5% from the slums.


Water Hyacinth Weeds:

  • The organic waste in these waterways acts as plant nutrient and several aquatic weeds are found growing. Water hyacinth is the principal weed that grows abundantly in the waterways. These floating weeds shelter mosquito larvae in between the plants and the green foliage offers a good daytime resting shelter for adult mosquitoes. These plants do not multiply faster in clear water bodies.
  • It is pertinent to point out here that the nuisance causing Culex (pest) mosquitoes do not breed in clear water. They need organically polluted water. Therefore prevention of organic pollution in these waterways is the first step towards prevention of mosquito breeding.

Rank Vegetation:

Over grown vegetation especially thorny bushes traps the floating hyacinth weeds. These shrubs and bushes reduce the accessibility for spraying. Periodical trimming / pruning of rank vegetation is a pre-requisite for mosquito control.

Minor Engineering:

Shoreline dressing, contour dressing, lidooing forms part of minor engineering towards prevention of breeding.

Sand Barrier Removal:

  • The entire effluents generated in the city finds it way into SWD/Minor drains and then into two major rivers namely Adayar and Coovum and finally discharge into Bay of Bengal.
  • The sand bar formation at the confluence of these rivers prevent free discharge. Periodical removal of sand bar by the PWD/WRO department is yet another important and vital engineering activity towards mosquito control. If the mouth of these rivers is kept wide open and perpendicular to the Bay, the seawater enters into the river system during high tide and during low tide period the river water gets discharged into the sea. The intrusion of seawater prevents mosquito breeding and the tidal wave action prevents stagnation in the river system.


Almost all the waterways are encroached upon preventing free flow of water besides disabling access for the spray men. Several stretches could not be covered for regular anti-larval spray work.

Solid Waste:

Solid waste disposal into the waterways by the residents living on the banks and commercial establishments not only prevents free flow of water but also enhances the mosquitogenic conditions.

Storm Water Drains:

  • As of now there is 800 Kms length network of storm water drains in the city. These drains are built to carry away rainwater during monsoon period and should remain dry during other seasons. But these drains are found with water stagnation throught the year leading to mosquito menace.
  • Geographically Chennai is a plain terrain and lacks natural gradient for free RUN off.

Action Taken By Corporation Of Chennai:

In the interest of protecting the public health, the Corporation of Chennai is under taking anti-mosquito measures at a huge cost.

De-weeding, removal of rank vegetation & floating solid waste, shoreline dressing, contour dressing followed by spraying of chemical and biolarvicides is undertaken in all the water ways on weekly frequency to control the mosquito breeding. Spraying of larvicide's in all the storm water drains is undertaken weekly once to control the mosquito breeding. Fogging of the Storm water drains with portable fog machines is undertaken during daytime to control the adult mosquitoes resting inside the drains. Vehicle mounted fog machines are operated during dusk hours to control the adult mosquito density.

Malaria In Chennai:

Chennai City has become an endemic area for malaria since few decades. Nearly 70% of the malaria cases recorded in the State of Tamil Nadu is occuring in Chennai City alone. The problem is more acute in Northeast coastal areas like Tondiarpet, Washermanpet, Royapuram, Harbour, Muthialpet, Mannady, Sowcarpet, Elephantgate, Periamet, Pattalam and Pulianthope.

Bio-environmental method for Malaria control:


"Anopheles Stephensi" the mosquito that transmit malaria in Chennai breeds in clear water men-made sources like wells, Over-Head-Tanks, sumps, Cisterns and other receptacles.
In order to bring down malaria a time bound Action Plan has been launched since November 2003 for source reduction by invoking sections 83&84 of Tamil Nadu Public Health Act 1939, under this enforcement, notices are served on the house owner/occupier to mosquito-proof the open wells, OHT's and sumps existing in their houses. Those who fail to comply are being prosecuted.

Q.B.C Test for Malaria - Free of cost:

Q.B.C.(Quantitative Buffycoat Analyser) Centres:

  • Corporation of Chennai is also contemplating to mosquito proof the source and recover the cost of doing so from the owner/occupier as though property tax.
  • Chemical larvicide's is being applied to wells, tanks, sumps, cisterns and other such clear water bodies once a week to prevent vector mosquito breeding.
  • Blood smear examination for malaria detection is made available at all Corporation dispensaries free of cost and on the spot diagnosis facility and treatment for malaria is available. In order to detect hidden cases which are not detectable under conventional peripheral blood smears examination technique, expensive QBC equipment is made available for highly specific diagnosis of malaria at the following centres free of charges for the benefit of the people.

Defective Drains

The reason for perennial presence of water in these drains is due to cross connections of sewage given by CMWS&SB. In addition, several house owners instead of obtaining a proper underground drainage connections have illegally connected their sewer line to storm water drains to avoid paying sewage tax and other charges to CMWS&SB.

Illegal Connections

  • The network of the SW Drains so far laid is such that there are several blind ends i.e. there is no outlets. As a result the water remains stagnant giving rise to mosquito breeding.
  • The usual design of the SWD has openings at every 10 mtr distance. As such spraying for control of mosquito larvae is possible only at the openings. If the water is flowing, the larvicide's sprayed can spread uniformly throught the length. Since all these drains are stagnating there is no scope for uniform coverage and therefore mosquito menace. At many places solid waste and debris is dumped into the SWD. This situation aggravates the mosquitogenic condition.
  • All these are MAN-MADE engineering defects which results in severe perennial mosquito menace besides spread of mosquito borne diseases


  • Dengue is currently the most important arboviral disease with 2.5 billion people living in areas of risk and tens of millions of cases occurring each year, affecting more than 100 countries. It is one of the most rapidly emerging mosquito borne disease in the world and W.H.O. has identified dengue as a re-emerging disease in South East Asia.
  • Dengue virus was first isolated in India during 1945. There are three forms of this disease. 1) Dengue Fever (DF) 2) Dengue Hemorrhagic fever (DHF) and 3) Dengue shock syndrome (DSS). Nearly 44% of DHF and DSS can be fatal. There are four serotypes namely Den 1, Den 2, Den 3 & Den 4.
  • In 1995. DHF became a leading cause of hospitalization and death among children in many Asian countries. In India the first outbreak of DHF/DSS was documented in Delhi 1985. But prior to this endemic transmission of all four dengue serotypes has been reported.
  • Aedes Aegypti is the main vector mosquito responsible for transmission of dengue. This mosquito has characteristic white stripes on the back and legs. Hence it is also called as Tiger mosquito. This mosquito rests indoors in closets and other dark places. Outside they rest where it is cool and shady. The female mosquito lays eggs in clean water containers in and around houses. This mosquito is a domestic breeder and breeding can occur in any water catching or water storage container such as wells, over-head-tanks discarded items tyres, utensils and large containers used for rain water collections which are not emptied and cleaned periodically. Since water is essential during the first 8 days in the life of the mosquito, emptying containers once a week will greatly reduce the risk of dengue fever. Aedes mosquito can fly upto a limited distance of 400 meters ( usually not more than 100 meters ) but can spread over vast distances mechanically in various types of vehicles used by man.

Clinical Manifestations

The symptoms of dengue fever are similar to acute viral fevers. These are sudden onset of fever, headache, bodyache, joint pains and retro-orbital pain. Other common symptoms include anorexia, altered taste sensation, constipation, colicky pain, abdominal tenderness, dragging pains in the inguinal region, sore throat and general depression. Patients may or may not have rash. Some of the patients may also show signs of bleeding from gum, nose etc.

The following are some of the reasons for the resurgence of dengue.

  • Expansion is geographical distribution of primary vector Aedes Aegypti.
  • Extensive increase in transport system which has increased in migration and immigration of infected humans.
  • Irregular potable piped water supply which compels the community to adopt storage practices in domestic containers, which are potential breeding sources of Ae-Aegypti.
  • Non biodegradable plastic material, discarded containers especially tyres left in the environment have increased man made breeding habitats of vector.
  • Lack of awareness among the people about the basic etiology of dengue virus and its mode of transmission.
  • No treatment or vaccine available for prevention.

Present Situation

  • The incidence is perennial and a spurt is noticed during September to November. The city experienced a severe outbreak during the year 2001.
  • Surveillance with major hospitals like ICH, Egmore and K.K. Child Trust Hospital. Nungambakkam is being maintained to obtain information about occurrence of dengue cases. The cases are registered and cross notified to concerned for preventive measures.
  • Vector control in case incidence areas like fogging/spraying and larval cross check to detect and eliminate the breeding sources is undertaken to prevent the spread.
  • So far the occurrence is sporadic and there is no clustering of cases indicating an outbreak.


A collaborative work with the Center for Research in Medical Entomology (CRME), Madurai, a wing of ICMR is under progress in Chennai.

The Zones V, VII & VIII have recorded more no of cases during the last few years. A Dengue surveillance is undertaken in Zones V, VII, VIII & X to monitor the prevalence. Blood samples from school children is also being collected for sentinel surveillance and antibodies are detected.

The study also indicated that discarded tyres, containers and cement cisterns are pre-dominant breeding sources.

Information, Education & Communication (IEC)

The study also indicated that only 3% of the people are aware of dengue, its transmission and prevention. Therefore IEC requires to be strengthened. The CRME conducted a workshop on Dengue in Chennai on 19th & 20th June 2003 specifically for developing an IEC package with WHO funds. Hand bills on dengue has been prepared and is widely distributed to public. Posters on dengue were pasted in all Corporation Dispensaries.


  • Leptospirosis is a zoonotic disease of world-wide distribution. The spectrum its clinical presentation and the tedious laboratory procedures required for its confirmatory diagnosis have made its recognition difficult in most of the instances and consequently it is grossly under-reported. Though it is considered as an occupational hazard in many countries, the environment and life style of people of the developing countries put the whole population of such countries at risk of acquiring leptospiral infection. The bacteria-Leptospira was identified in 1915 and its association between Weil's Disease and many other clinical syndromes like Seven Day Fever, Canicola Fever etc. has been known for the past many decades. Though the disease has a worldwide distribution, surveillance against it is restricted to a few countries.
  • During the first few decades of this century, the disease had been reported from many parts of the country based purely on clinical suspicion. Bacteriological confirmation of the presence of human leptospiral infection in the country was first reported from Andaman islands in 1929. Later, it was reported from other places like Bombay, Calcutta and Assam. All these were isolated reports from localised areas.
  • Since leptospirosis presents in a wide variety of clinical forms, identification of suspects on clinical grounds is not possible in many instances. The association between Weil's Disease and leptospirosis is so strong in the minds of etiology is never suspected. This leads to a significant proportion of the cases going unnoticed. Hence the necessity to formulate a broad-based clinical definition was felt by delegates and the following case definition was agreed upon:


Any patient reporting with fever, body aches, headache with any of the following:

  • Jaundice
  • Oliguria
  • Cough, haemoptysis and breathlessness
  • Haemorrhagic tendencies including haemetemesis, bleeding gums and subconjunctival haemorrhage
  • Signs of meningeal irritation and convulsions

Should be suspected as a case of leptospirosis and investigated.

Notification Of The Disease

  • Since leptospirosis is not notifiable in India, most of the instances of its occurrence do not get registered. This leads to underestimating the problem in the country. To make accurate estimates of the incidence and loss of life and economic loss due to it, the disease should be made notifiable.
  • Leptospirosis is Zoonotic disease caused by bacteria called Leptospires. Rodents are natural reservoir for the leptospires. Man acquires this infection when he comes in contact with water contaminated with urine of rats.
  • The symptoms include fever with chill, headache, body pain, joints pain, redness of the eyes, vomitting, jaundice and blood stained urine.
  • This disease mimics several other diseases and hence requires laboratory tests for confirmation , urine and blood samples are tested for diagnosts.
  • The test for confirmation of Leptospirosis is available at Madras Medical College. Tamil Nadu University for Veterinary and Animal Sciences field station at Madhavaram and at few other hospitals.
  • Avoiding contact with contaminated water, avoiding bathing in lakes and ponds. Safe disposal of sewer water, prevention of rodent infestation and seeking medical advice in case of fever associated with jaundice symptoms are some of the measures to be adopted to protect oneself from Leptospirosis. This disease can be easily treated with antibiotics if diagnosed early.