Abstract
As malaria declines in many African countries there is a growing realization that new interventions need to be added to the front-line vector control tools of long-lasting impregnated nets (LLINs) and indoor residual spraying (IRS) that target adult mosquitoes indoors. Larval source management (LSM) provides the dual benefits of not only reducing numbers of house-entering mosquitoes, but, importantly, also those that bite outdoors. Large-scale LSM was a highly effective method of malaria control in the first half of the twentieth century, but was largely disbanded in favour of IRS with DDT. Today LSM continues to be used in large-scale mosquito abatement programmes in North America and Europe, but has only recently been tested in a few trials of malaria control in contemporary Africa. The results from these trials show that hand-application of larvicides can reduce transmission by 70-90% in settings where mosquito larval habitats are defined but is largely ineffectual where habitats are so extensive that not all of them can be covered on foot, such as areas that experience substantial flooding. Importantly recent evidence shows that LSM can be an effective method of malaria control, especially when combined with LLINs. Nevertheless, there are a number of misconceptions or even myths that hamper the advocacy for LSM by leading international institutions and the uptake of LSM by Malaria Control Programmes. Many argue that LSM is not feasible in Africa due to the high number of small and temporary larval habitats for Anopheles gambiae that are difficult to find and treat promptly. Reference is often made to the Ross-Macdonald model to reinforce the view that larval control is ineffective. This paper challenges the notion that LSM cannot be successfully used for malaria control in African transmission settings by highlighting historical and recent successes, discussing its potential in an integrated vector management approach working towards malaria elimination and critically reviewing the most common arguments that are used against the adoption of LSM.
Highlights
The United Nation’s Roll Back Malaria decade 2000-2010 has seen an unprecedented increase in the coverage of malaria control interventions
Insecticides available for larval control have different modes of action including (1) surface films like mineral oils and alcohol- or silicon based surface products that suffocate larvae and pupae, (2) synthetic organic chemicals such as organophosphates that interfere with the nervous system of immature stages, (3) microbials such as Bacillus thuringiensis israeliensis (Bti), and Bacillus sphaericus (Bs) that kill larvae with toxins that are ingested and lead to lysis of the insect’s gut, and (4) insect-growth regulators such as pyriproxyfen, methoprene and diflubenzuron that interfere with the metamorphoses of the insect and prevent adult emergence from the pupae stage
This paper challenges the notion that larval source management (LSM) cannot be successfully used for malaria control in African transmission settings by highlighting historical and recent successes, discussing its potential in an Integrated Vector Management (IVM) approach working towards malaria elimination and critically reviewing the most common arguments that are used against the adoption of LSM
Summary
The United Nation’s Roll Back Malaria decade 2000-2010 has seen an unprecedented increase in the coverage of malaria control interventions. Several authors have convincingly shown that the limitations of LLINs/ITNs and IRS are largely defined by mosquitoes avoiding them by feeding or resting outdoors and/or at earlier hours and by developing insecticide resistance [82,83,85,86,87,88,89,91,92, 105,106] These concerns can be reduced if LSM is combined with indoor vector control tools. Many argue that LSM is not feasible in Africa due to the high number of small and temporary larval habitats for An. gambiae that are difficult to find and treat promptly, that the delivery of larvicides to very small habitats (e.g. cattle hoof prints) is difficult, and environmental management targets primarily larger, permanent water bodies, which are not typically anopheline habitats and contribute little to malaria control [16,17]. Human resources need to be improved to ensure that any improved control can be sustained [74,149,150]
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