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July 20, 2019

Factors causing dengue fever spread, awareness must to avoid outbreaks


July 20, 2019

Islamabad : The population of dengue fever vector aedes aegypti fluctuates with temperature, rainfall and humidity as it is high in rainy season and low in extreme hot weather and during rainy season, the risk of virus transmission by the vector is greater. Dengue infections are generally occurred during or after rain, as an outcome of rise in vector population.

Preventing or reducing dengue virus transmission depends entirely on controlling the mosquito vectors or interruption of human–vector contact. Control measures are necessary as dengue fever (DF) and dengue haemorrhagic fever (DHF) cases increase proportionally with the larval density.

This is high time to start social mobilization to contact community to look for sites and places inside or outside homes that can attract rain water and provide a favourable place for the female aedes mosquitoes to breed, said District Health Officer Islamabad Dr. Muhammad Najeeb Durrani while talking to ‘The News’ on factors causing dengue fever spread.

He added that as an epidemiological finding, a surge in dengue fever cases is always expected after the rains particularly in monsoon in this region of the country and at the time when an outbreak is already occurring in adjoining areas, districts or other parts of the country.

During monsoon, the chemical elimination of mosquitoes by using adulticides is of minimal use and thus we need community participation to avoid dengue fever spread, he said.

The dengue mosquitoes both aedes aegypti and aedes albopictus are vectors for causing dengue fever as the female mosquitoes carry one of the four types of dengue virus from the dengue patient to the healthy person and transmit the disease, he explained.

He added the optimal temperature for aedes aegypti larvae is 28 degree centigrade and above this, the rate of development is high and below 18 degree centigrade, the growth gets prolonged. Above 36 degree centigrade, the larval development is not complete. Extreme hot and dry weather may kill most of the eggs and render adult vectors inactive, he said.

He added that people must be aware of the fact that the larval density starts from May to July. “The maximum Aedes aegypti larval density is noticed during July to October during rainy season reaching its peak in September.”

He said the viruses are passed on to humans through the bites of an infective female Aedes mosquito, which mainly acquires the virus while feeding on the blood of an infected person. Within the mosquito, the virus infects the mosquito mid-gut and subsequently spreads to the salivary glands over a period of 8-12 days. After this incubation period, the virus can be transmitted to humans during subsequent probing or feeding, he said.

The mosquitoes need artificial container of any type metal, glass, stone, plastic, rubber etc. even empty hole of tablet’s blister, or small natural water bodies like tree holes to lay eggs. Eggs they hatch can last from few days to several months, said Dr. Durrani.

He added the dynamics of aedes mosquitoes’ population present a strong seasonal variability with a six months period of adult activity and a six months period of egg diapauses.

The effects of temperature, rainfall and artificial flooding (man-made watering of lawns, fields and water spillage) are the genuine factors besides movement of infected patients from areas where there has recently been an outbreak of dengue fever to cause the disease, he said.

He added the flight range studies suggest that most female aedes aegypti may spend their lifetime in or around the houses where they emerge as adults and they usually fly an average of 400 metres. This means that people, rather than mosquitoes, rapidly move the virus within and between communities and places, he said.

Proper solid waste disposal and improved water storage practices, including covering containers to prevent access of egg-laying female mosquitoes are among methods that are encouraged through community-based programmes, he said.

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