Outcomes

Anticipated absolute effects per year

Relative Effect

(95% CI)

No of Participants

(studies)

Quality of the evidence

(GRADE)

Risk without LSM (Control)

Risk difference with LSM (95% CI)

Malaria incidence (Cluster RCT)

6.5 per 100

4.5 fewer per 100 (from 4.48 to 5.07 fewer)

RR 0.26 (0.22-0.31)

20,124 (2)

Moderate^1,2,3,4

Malaria incidence (Controlled before-after)

23.2 per 100

11.37 fewer per 100 (from 19.02 fewer to 10.21 more per 100)

RR 0.51 (0.18-1.44)

98,233 (3)

Low^5,6,7,8

Parasite prevalence (Cluster RCT)

4.4 per 100

3.92 fewer per 100 (from 3.43 to 4.18 fewer)

RR 0.11 (0.05-0.22)

2963 (1)

Moderate^4,9,10

Parasite prevalence (Controlled before-after)

15.7 per 100

10.68 fewer per 100 (from 7.06 to 12.72 fewer)

RR 0.32 (0.19-0.55)

8041 (5)

Moderate^{11,12,13,14,15}

Adverse Events: None reported.

1. Downgraded by 1 for serious risk of bias: Both studies were described as randomized but did not adequately describe a process to reduce the risk of selection bias.
2. No serious inconsistency: There was no statistical heterogeneity.
3. No serious indirectness: Both studies were conducted in rural Sri Lanka. The primary vectors were An. culicifacies and An. Subpictus and the primary mosquito larval habitats were river bed pools, streams irrigation ditches and rice paddies, and abandoned gem mine pits. The intervention was larviciding with pyriproxyfen approximately every six months. Generalization of this result to wider settings is supported by the findings from the non-randomized studies.
4. No serious imprecision: Although these studies did not adjust for the cluster design, a sensitivity analysis adjusting this result for the cluster design suggested the result is likely to be both statistically significant and clinically important.
5. Downgraded by 1 for risk of bias: In two of these studies, there were important baseline differences in malaria incidence between groups. The incidence was higher in the intervention group pre-intervention and reduced to similar levels as the control group post-intervention.
6. Not downgraded for inconsistency: There was heterogeneity in this result which can be explained by baseline differences in two of the studies. However, there was a reduction in malaria incidence in the intervention groups in all three studies.
7. No serious indirectness: One study was conducted in rural India where the primary vectors were An. fluviatilis and An. culicifacies, the main larval habitats of which were streams, stagnant pools, ditches and irrigation channels. A dam was constructed across the stream, reducing the number of larval habitats in the intervention village. One study was conducted in highland villages in rural Kenya, where the major vectors were An. gambiae and An. funestus. The primary larval habitats were small streams and papyrus swamps, which were treated weekly with Bs for six months and then Bti for 13 months. One study was conducted in a desert fringe area of urban India where the primary vectors were An. culicifacies and An. stephensi, the main larval habitats of which were containers, wells, canals and rainwater pools and drains. Larviciding with pirimiphos-methyl was conducted weekly for 15 months.
8. Downgraded by 1 for imprecision: The overall effect is not statistically significant but is difficult to interpret due to the baseline differences.
9. Downgraded by 1 for serious risk of bias: This study was described as randomized but did not adequately describe a process to reduce the risk of selection bias.
10. No serious indirectness: This single study was conducted in rural Sri Lanka where the primary larval habitats were abandoned gem mine pits and the findings may not be easily generalized elsewhere. However generalization of this result to wider settings is supported by the findings from the non-randomized studies.
11. No serious risk of bias: the risk of bias inherent in these non-randomized studies is already accounted for in the initial downgrading to ’low quality evidence’.
12. No serious inconsistency: All five studies showed a large benefit with LSM. The smallest effect was a 40% reduction in malaria prevalence which is still considered clinically important.
13. No serious indirectness: These five studies were in conducted in urban and rural settings in Greece, Tanzania, India and the Philippines. Mosquito larval habitats ranged from man-made habitats, containers and wells to rainwater pools, irrigation channels, ditches and streams, and interventions included dam construction, flushing of streams, straightening or lining of streams, drainage of marshland and larviciding.
14. No serious imprecision: All studies showed clinically important and statistically significant effects.
15. Upgraded by 1 as the effects seen were large. Two studies had smaller effects and baseline differences which would lead to an underestimation of the true effect

Findings

Interpretation

Equity - Which of the PROGRESS groups examined

All but one of the included studies were conducted in low- and middle-income countries. The interventions occurred in mostly rural but some urban locations.

LSM is effective in the prevention of malaria in most malaria-endemic countries and in both urban and rural communities.

Equity Applicability

LSM is effective for malaria prevention in malaria-endemic countries in Africa, Asia, and Europe. LSM may be effective in other settings, however trials may have been conducted in settings in which success was likely. The effectiveness of LSM was consistent across the different included studies and the different interventions.

LSM is an effective intervention for malaria prevention and the results are likely applicable to other settings provided the interventions have been tailored to the local ecology and infrastructure. The feasibility of the intervention could be different in other settings, depending on the number, type, and accessibility of larval habitats.

Each type of LSM is appropriate for different environments and while interventions may be combined they each of different requirements. The application of larvicide is labour intensive and requires regular treatment of the larval habitats which requires a well-managed system for application, surveillance, and evaluation.

Policymakers implementing and LSM intervention need to ensure that the appropriate intervention for the local environment and larval habitats is chosen and an appropriate management system is in place to ensure adequate application and surveillance.

Cost-equity

The review did not report on the cost-effectiveness of LSM.

Policymakers who wish to implement an LSM program need to weight the costs and benefits and consider the resources required for LSM including:

- those required for habitat modification

- resources for larvicide including the larvicide as well as personnel to apply it on a regular basis and monitor it’s effectiveness to ensure the correct dosage and frequency of application

- the number, type, and accessibility of larval habitats.

LSM may improve cost-equity since the people most at risk for malaria are also the most disadvantaged.

Large applications of LSM can reduce inequities since those protected are likely to be those who may not be able to afford insecticide treated bednets and their retreatment, or indoor residual spraying. In addition, LSM provides protection from malaria outside of the house by reducing the number of adult mosquitos that can bite.

Monitoring & Evaluation for PROGRESS groups

LSM is an additional policy option to insecticide-treated bednets and indoor residual spraying for reducing malaria morbidity when a sufficient proportion of larval habitats can be targeted. Ongoing surveillance is required for both entomological indicators (mosquito and larval) and human health outcomes to ensure program effectiveness.

Policymakers implementing and LSM intervention need to ensure an appropriate evaluation and monitoring plan is in place to ensure effectiveness of the intervention. This will include evaluation of the LSM application as well as monitoring clinical outcomes, such as malaria incidence and parasite prevalence.