Dengue is viral disease, transmitted by bites of female adult Aedes mosquitoes. This mosquito breeds in containers like cement tanks, overhead tanks, underground tanks, tyres, desert coolers, pitchers, discarded containers, junk materials, potholes, rooftop, window parapet, ornamental fountain, lucky bamboo pot, money plant bottle etc., in which water stagnates for more than a week.
These containers are usually found in and around houses. The breeding of Aedes mosquitoes can primarily be eliminated by cleaning, drying and keeping the water containers tightly closed so that the adult mosquitoes are not able to lay their eggs. The co-operation from the community in this regard helps to keep the dengue under check.
In addition, the breeding sites are treated with chemicals like Temephos liquid and granules. The drains are treated with bio-larvicide. Insect Growth Regulators like Diflubenzuron and Pyreproxifen have also been recommended as larval control.
These larvicides are sprayed by the staff of Municipal Corporations. To prevent mosquito bite, personal protection with full sleeve clothing, use of repellents like mosquito coils, mats etc. are also advised. Use of bed-nets to protect infants and night workers while sleeping in daytime also helps in preventing mosquito bite.
The enforcement of byelaws to strengthen source reduction at community level and anti-larval activity at construction sites through builders have also been one of the important tools towards keeping the disease under check. Ministry of Urban Development has been asked to monitor the rigorous implementation of byelaws and amendments as per present requirement.
Adult Aedes mosquitoes can be killed by fogging. Pyrethrum spray is used in indoor situations as space spray. Malathion fogging is used outdoor using insecticide Malathion technical mixed with diesel. Cyphenothrin 5% EC- another molecule is also recommended in the programme for fogging which can be used both for indoor and outdoor fogging.
Fogging is recommended only in case of outbreak/epidemic situation to contain the upsurge in dengue cases. This has been the principal method of dengue control used by most countries as per WHO during outbreak situation.
With a view to control the recent upsurge in dengue cases, the fogging was resorted to kill the adult mosquito by prioritizing the areas with high larval density as well as reports of cases coming from affected areas. As per WHO, the area within a radius of 400-500 metre of the affected house should be covered. It has also been documented by WHO that in several countries, thorough treatment at an interval of 1-2 weeks with portable fogging applicators together with truck mounted applicators yielded control of Aedes mosquitoes.
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Even though diesel is used in fogging as carrier for insecticide, the temperature at which the diesel mixed with insecticide comes out as fog is less than the burning temperature of diesel as is the case in diesel driven vehicles. This can be noted from the colour of the smoke which is white in fogging and black in vehicles. The white fog which dissipates quickly is usually not harmful and is recommended to control much more serious public health hazards like Dengue.
The fogging is recommended usually in dawn and dusk because the temperature is comparatively cooler and adult Aedes mosquitoes are most active at these hours.