Environmental management seeks to change the environment in order to prevent or minimize vector propagation and human contact with the vector-pathogen by destroying, altering, removing or recycling non-essential containers that provide egg/ larval/ pupal habitats. Such actions should be the mainstay of dengue vector control. Three types of environmental management are defined:
- Environmental modification – long-lasting physical transformations to reduce vector larval habitats, such as installation of a reliable piped water supply to communities, including household connections.
- Environmental manipulation – temporary changes to vector habitats involving the management of “essential” containers, such as frequent emptying and cleaning by scrubbing of water-storage vessels, flower vases and desert room coolers; cleaning of gutters; sheltering stored tyres from rainfall; recycling or proper disposal of discarded containers and tyres; management of plants close to homes that collect water in the leaf axils.
- Changes to human habitation or behaviour – actions to reduce human–vector contact, such as installing mosquito screening on windows, doors and other entry points, and using mosquito nets while sleeping during daytime.
Improvements in, and maintenance of, urban infrastructure and basic services contribute to the reduction in available larval habitats since large Ae. aegypti populations are often associated with poor water supply and inadequate sanitation and waste disposal services.
Improvement of water supply and water-storage systems
Improving water supplies is a fundamental method of controlling Aedes vectors, especially Ae. aegypti. Water piped to households is preferable to water drawn from wells, communal standpipes, rooftop catchments (rain water harvesting) and other water-storage systems.
However, potable water must be supplied reliably so that water-storage containers that serve as larval habitats – such as drums, overhead or ground tanks and concrete jars – are not necessary. The installation of reliable piped water supplies to houses should be accompanied by a communication strategy that discourages traditional storage practices.
Mosquito-proofing of water-storage containers
Water-storage containers can be designed to prevent mosquitoes from laying eggs on the surface of the water. Containers can be fitted with tight lids or, if rain-filled, tightly-fitted mesh screens can allow for rainwater to be harvested from roofs while keeping mosquitoes out. Removable covers should be replaced every time water is removed and should be well maintained to prevent damage that permits mosquitoes to get in and out.
Expanded polystyrene beads used on the surface of water can prevent mosquitoes from laying eggs on the surface. However, these are only applicable in storage containers with an installed pipe to draw water from the bottom.
Solid waste management
In the context of dengue vector control, “solid waste” refers mainly to non-biodegradable items of household, community and industrial waste. The benefits of reducing the amount of solid waste in urban environments extend beyond those of vector control.
Applying many of the basic principles can contribute substantially to reducing Ae. aegypti larval habitats. Proper storage, collection and disposal of waste are essential for protecting public health. The basic rule of “reduce, reuse, recycle” is highly applicable. Efforts to reduce solid waste should be directed against discarded or non-essential containers, particularly if they have been identified in the community as important mosquito-producing containers.
Solid waste should be collected in plastic sacks and disposed of regularly. The frequency of collection is important: twice per week is recommended for housefly and rodent control in warm climates. Integration of Ae. aegypti control with waste management services is possible and should be encouraged.
A reliable and regular street cleansing system that removes discarded water-bearing containers and cleans drains to ensure they do not become stagnant and breed mosquitoes will both help to reduce larval habitats of Ae. aegypti and remove the origin of other urban pests.
During the planning and construction of buildings and other infrastructure, including urban renewal schemes, and through legislation and regulation, opportunities arise to modify or reduce potential larval habitats of urban disease vectors, including Ae. aegypti, Culex quinquefasciatus and An. stephensi. For example, under revised legislation in Singapore, roof gutters are not permitted on buildings in new developments because they are difficult to access and maintain. Moreover, property owners are required to remove existing gutters on their premises if they are unable to maintain them satisfactorily.