Dengue control

The mosquito

The Aedes aegypti mosquito is the main vector that transmits the viruses that cause dengue. 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. The immature stages are found in water-filled habitats, mostly in artificial containers closely associated with human dwellings and often indoors.

Flight range studies suggest that most female Ae. 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.

Dengue infection rates are higher outdoors and during daytime, when these mosquitoes (Stegomyia) bite most frequently. However, Ae. aegypti breed indoors and are capable of biting anyone throughout the day. The indoor habitat is less susceptible to climatic variations and increases the mosquitoes’ longevity.

Dengue outbreaks have also been attributed to Aedes albopictus, Aedes polynesiensis and several species of the Aedes scutellaris complex. Each of these species has a particular ecology, behaviour and geographical distribution. Ae. albopictus is primarily a forest species that has become adapted to rural, suburban and urban human environments. In recent decades Aedes albopictus has spread from Asia to Africa, the Americas and Europe, notably aided by the international trade in used tyres in which eggs are deposited when they contain rainwater. The eggs can withstand very dry conditions (desiccation) and remain viable for many months in the absence of water and the European strain of Aedes albopictus can undergo a period of reduced development (diapause) during the winter months.

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