New review published! Larviciding to prevent malaria transmission

Plain language summary

What was the aim of this review?

Larviciding is the regular application of microbial or chemical insecticides to water bodies or water containers. The aim of larviciding is to reduce the adult population of mosquitoes by killing the aquatic immature forms, so that fewer will develop into adults. This should reduce the number of mosquitoes that bite and infect humans with malaria.

Key messages

All four studies included in this review distributed larvicides manually. Hand larviciding of small mosquito habitats may be effective in preventing malaria. Only one study was conducted in an area where larval habitats spanned a large area and this study found no effect of larviciding.

What was studied in the review?

We searched for trials that evaluated the impact of larviciding, using a microbial agent or chemical insecticide on malaria transmission. We considered effects on both human health outcomes and on mosquito populations.

What were the main results of the review?

Evidence from three studies shows that larviciding may decrease at least one malaria disease outcome in some studies, and this was in areas where the mosquito aquatic habitats were less than 1 km2 (lowcertainty evidence). We do not know if larviciding in large water bodies shows an impact on malaria based on results from one study in The Gambia (very lowcertainty evidence).

How up to date is the review?

We searched for relevant trials up to 6 June 2019.

Authors’ conclusions

Implications for practice

The WHO currently recommends larviciding and other larval source management (LSM) interventions as a supplementary malaria control intervention. Unlike insecticidetreated nets (ITNs) and indoor residual spraying (IRS) which target indoor vectors, LSM could potentially target outdoor as well as indoor transmission. As a result, many programmes in the elimination phase are now considering LSM including larviciding to tackle the remaining foci of malaria transmission. This review supports the use of ground larviciding for nonextensive larval habitats. We do not know if larviciding by hand in extensive habitats, largely inaccessible on foot or where water is tidal has any effect on malaria based on the results of one study of very lowcertainty evidence. Operational research could strengthen the evidence base in these particular settings, with an aim of identifying effective methods for distributing larvicides over large areas

Most countries do not have the capacity or capability to conduct larviciding. If malaria control programmes are to implement larviciding, then support will be required to assess feasibility, and implement, and monitor and evaluate the intervention.

Implications for research

The findings of this review indicate lowcertainty evidence of benefit from controlled studies; however, the reality is that few, if any, studies will be conducted in the coming years. Further evidence on the effects of larviciding should be generated through monitoring and evaluation of programmatic implementation using concurrent control areas, perhaps in pragmatic stepped wedge designs.

Although not evaluated or discussed in this review, evaluation of new technologies for identifying aquatic habitats (such as highresolution imaging) and aerial application of larvicides in malariaendemic areas may well be relevant to further refine larviciding strategies.

Choi  L, Majambere  S, Wilson  AL. Larviciding to prevent malaria transmission. Cochrane Database of Systematic Reviews 2019, Issue 8. Art. No.: CD012736. DOI: 10.1002/14651858.CD012736.pub2.