Protection for communities
There are several methods of controlling mosquitoes at a camp or community level. These work by reducing the number of mosquitoes, and/or the average age of mosquitoes in an area. The average age is important: if most mosquitoes don’t live longer than 10-14 days they will not live long enough to pass on the malaria parasite.
Indoor residual spraying or IRSThe application of this protective measure involves spraying a long lasting insecticide indoors onto the walls and ceilings of all rooms. The insecticide typically lasts for 3-6 months when it then needs to be reapplied. Indoor residual spraying (IRS) results in fewer mosquitoes coming indoors and, more importantly, it kills any mosquitoes that rest on the sprayed areas. Through IRS the incidence of malaria can be drastically reduced.
IRS works best when the target mosquito species prefers to bite indoors and to rest indoors either before or after biting. IRS can also have a significant impact on mosquitoes that prefer biting outdoors, but tend to rest indoors after feeding. These mosquitoes often choose to rest in animal sheds and outhouses so spraying the ceilings and walls of these is often as important as spraying the dwellings themselves. In several areas in the Asia-Pacific the outdoor resting and feeding habits of the main vectors means that IRS may not be sufficient to control transmission. Where transmission is exclusively forest-based, providing IRS in villages will have no impact on transmission at all.
Whilst IRS may appear simple in theory, it is in fact difficult to do properly. To be fully effective spraying needs to be carried out in every room (and where appropriate in every outbuilding), in every household in the target community. This requires a high level of community acceptance. It must be carried out by trained spray personnel using specialized spray equipment and appropriate safety gear. Poor spraying results in patchy coverage allowing mosquitoes to find unsprayed patches of wall to rest on thus reducing the effectiveness of the approach. Where transmission of malaria fluctuates seasonally the timing of IRS is critical. Campaigns should be timed to take place at the very early stages of any expected seasonal increase. Large scale IRS requires detailed and rigorous planning, management and supervision. In 2013 WHO produced an updated operational manual on IRS for malaria control and elimination, which provides an in-depth resource.
Insecticide treated wall linings
Insecticide treated wall linings have a similar effect to IRS. The wall linings, which are similar to wall paper, are available in rolls about a meter wide. They are cut to size and pasted onto the inside walls of a house. Wall linings ensure even coverage of insecticide without the need for specialized training and equipment. Insecticide is gradually released to provide effective vector control over a period of several years thus avoiding the problems of low user compliance that are associated with the regular reapplication required in the case of IRS.
Larval control / environmental management
Reducing the number of places where mosquitoes can lay eggs, or treating these places with chemical or biological products to kill mosquito larvae reduces the number of adult mosquitoes in an area. This is termed source reduction.
Environmental management can be applied to reduce the number of existing breeding sites and to minimize the creation of new breeding sites, for example during construction work. It can take the form of permanent environmental modification (e.g. draining swamps, preventing seepage from canals, installing effective drainage systems) and ongoing environmental manipulation to ensure unfavourable conditions for vector breeding (e.g. water level management in rice paddies and shrimp farms).
In some Asian-Pacific settings environmental management has been shown to work well, for example in Indonesia and the Solomon Islands successes have been achieved through development of specific draining regimes for rice paddies and managing salinity levels in aquaculture3.
A number of reports relevant to environmental management for vector control are available from WHO.
Larval control requires the regular application of chemical and biological insecticides to breeding sites. In general, larviciding should only be considered for malaria control in areas where the breeding sites are few, fixed and findable.
Measures that reduce vector longevity, such as ITNs and IRS, have greater potential impact than measures that reduce only vector density, such as environmental management and larviciding. Generally measures that reduce adult densities should only be used as a supplement to ITNs or IRS; only in a very few specific circumstances with low transmission will it be appropriate to deploy source reduction methods alone.
Long Lasting Insecticidal Nets (LLINs) as a community-wide control measure
Given the cost effectiveness of LLINs, they are commonly used as a community-wide control measure. This involves large scale distribution to all households through community-wide campaigns. This approach is used in most countries in the Asia-Pacific. LLINs reduce malaria parasite transmission mainly by killing or blocking mosquitoes that attempt to feed on humans sleeping under nets.
While the impact of wide scale LLINs usage on incidence of malaria in settings where outdoor early biting mosquitoes are more common will be lower than in areas with predominantly late night indoor biting vectors, this intervention is still shown to provide useful protection against mosquitoes.
Other community-wide control methods
Fogging and space spraying
Fogging or space spraying is the release of insecticide into the air as smoke or fine droplets. It is primarily reserved for emergency situations such as epidemics of dengue fever. Fogging has not been shown to be effective in any malaria-endemic areas. Fogging and area sprays must be properly timed to coincide with the time of peak adult mosquito activity, because resting mosquitoes are often found in areas that are difficult for the insecticide to reach (e.g., under leaves, in small crevices). In addition, fogging and area spraying will have to be repeatedly applied to have an impact, and it can easily become too costly to maintain or result in the overuse of insecticides.
This table gives an overview of the recommended control approaches, by country in the Asia-Pacific region.
ADDITIONAL RESOURCES
on the prevention of malaria