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November 12, 2015

Ways & means to control dengue fever outbreaks during off-season


November 12, 2015

During the off-season, the main action against dengue vectors is reportedly fogging (space spraying) with insecticides, followed in frequency by water treatment of stagnant water ponds and over flowing water in buildings by temephos granules, container checking and health education to community.
Also visits by inspectors from the vector control section of the health departments are required to sites that are regarded as hot spots as a regular feature. Solid waste remains a major risk factor and its swift disposal is the main challenging job for the municipal authorities and the local government departments.
Assistant District Health Officer at Islamabad Capital Territory Health Department Dr. Najeeb Durrani, who is a member of The Global Outbreak Alert and Response Network (GOARN), expressed this while talking to ‘The News’ on Wednesday on what is needed to be done particularly during off season to make twin cities of Islamabad and Rawalpindi dengue-free in future, in 2016.
He said the outbreak in Islamabad has come to an end and only three confirmed patients of the infection have been undergoing treatment in the federal capital on Wednesday, at Pakistan Institute of Medical Sciences while no case of the infection has been reported in last two days.
Dengue fever, which is the fastest re-emerging arboviral disease in the world, imposes a heavy economic and health burden on countries, families and individual patients. In the absence of an effective drug or vaccine, the only strategic options presently available are case management to prevent death and vector control to reduce viral transmission, he added.
He said large dengue outbreaks continue to occur every year and the disease is extending to new geographical areas. In general, high humidity and temperature are conditions that favour mosquito survival, increasing the likelihood of transmission that requires an infected traveler in the season, he explained.
To a query, he

said dengue outbreaks can occur anytime, as long as the mosquitoes are still active, however, in general, high humidity and temperature play vital role in transmission of the disease. The best preventive measure for areas infested with Aedes Aegypti mosquito is to eliminate the mosquitoes’ egg laying sites – called source reduction. Lowering the number of eggs, larvae and pupae will reduce the number of emerging adult mosquitoes and the transmission of the disease, he said.
He added that in general, the egg laying sites are surfaces of water containers including drums, pitchers and like items so it is necessary to clear these utensils by scrubbing. He said a female Aedes mosquito lays 200 to 300 eggs which can survive for months and transform into larvae and pupae and then into adult mosquitoes on getting suitable temperature and aquatic conditions even after six months.
He suggested that items that collect rainwater or are used to store water should be covered or properly discarded. The remaining essential containers should be emptied and cleaned and scrubbed to remove eggs at least once a week. This will avoid the adult mosquitoes to emerge from the egg, larva or pupa stage. The underground and the overhead water tanks and water containers should be scrubbed for removing any eggs that might have been laid by the mosquitoes in the end of dengue fever season before the winter falls. These eggs if not removed will transform into mosquitoes after hatching in next summer when the weather both temperature and humidity become favorable, he explained.
To a query, he said in fact, the community participation is the key to dengue prevention. As every household aims to reduce vector density, the transmission rate will decrease or maybe even stop.
He added adult mosquitoes usually rest indoors in dark areas (closets, under beds, behind curtains). Here it is protected from wind, rain and most predators, which increases its life expectancy and the probability that it will live long enough to pick up a virus from one person and pass it on to the next, he said.
Dr. Durrani is of the view that since the temperature sensitive mosquitoes are at this point in time are moving indoors in search of warmer places to stay protected and maintain their ability to move and fly; this is high time that the community should know to kill these indoor mosquitoes with insecticide residual spray and secondly the windows and door screens are advised to be installed at the entry points of every house.
He said that mosquito nets or insecticide-treated nets should be stock piled by the health departments and the National Malaria Control Programme in ample amount for the next dengue season that may start in August and ends in the month of November. Household insecticides aerosols, mosquito coils or other insecticide vaporizers may reduce biting activity, he said.
Individuals must clear indoor hot spots including flower vases and saucers, water storage tank including domestic drinking water, bathroom etc, plastic containers and bottles while outdoor hot spots including discarded bottles and tins, discarded tyres, artificial containers, tree holes, potholes, construction sites, drums for collecting rainwater, shells, husks, pods from trees and leaf axils of various plants are needed to be removed or cleared from eggs, concluded Dr. Durrani.

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