Cochrane review finds larvae control cuts malaria cases

Spraying Mosquito Larvae_Flickr_Global Environment Facility (GEF)
Copyright: Flickr/Global Environment Facility (GEF)

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  • Larval source management includes land drainage and larvicide use
  • The technique was displaced by insecticide spraying and treated nets
  • But the report finds that the technique could cut malaria infections by 90 per cent in some places

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[LONDON] Targeting mosquito larvae could cut malaria cases by up to 75 per cent in some sites, and malaria infections by up to 90 per cent, a review published today has found.
The Cochrane review reports that a set of control methods, known collectively as larval source management (LSM), which kill mosquito larvae before they become malaria-carrying adults, could dramatically cut the disease's spread.
In some places, where the environmental conditions are right, this control method could reduce the number of people infected with the parasite by as much as 90 per cent, according to the review.
LSM techniques, which include draining land, adding larvicide to standing water or introducing animals that eat mosquito larvae, could boost malaria control efforts at a particularly challenging time for global malaria control.
"Malaria control is currently faced by various challenges, such as resistance to the main antimalarial drugs and insecticides, and new tools such as LSM are going to be increasingly needed," says lead author Lucy Tusting, a researcher from the London School of Hygiene & Tropical Medicine, United Kingdom.
Some malaria-endemic countries in Sub-Saharan Africa are already implementing LSM programmes, but there has been a lack of consensus on how effective the method is.
Tusting and her team's report is the first large-scale review of the effectiveness of larval source management.
"LSM fell out of favour when indoor residual spraying with [the pesticide] DDT was developed in the 1950s, and then insecticide-treated nets were developed and LSM was very much sidelined as an intervention," says Tusting. "It's only been in the last decade or so that there's been renewed interest in it. So a number of studies were then conducted that met the modern standards in epidemiology to test LSM. And our review is the first of its kind to systematically collate all those studies."

“New tools such as LSM are going to be increasingly needed.”

Lucy Tusting, London School of Hygiene & Tropical Medicine

The researchers looked at 13 LSM trial sites in Sub-Saharan Africa and Asia, and one from Greece.

They found that the technique is not effective everywhere. It has the greatest impact in places with high population densities and relatively small and accessibly mosquito breeding sites.
"Larval source management is an intervention that you have to tailor to the local ecology, the local mosquito species, where it breeds, where it breeds in relation to people, and how easy it is to target those breeding sites," Tusting says. "And all those factors will come together and determine how effective LSM can be. It might be that in some places it's just not appropriate at all.
"For example, one of our studies was carried out in the Gambia, where there are very large breeding sites in the flood plains along the Gambia River and rice paddies that stretch for many miles. And in that setting, LSM didn't show any protective benefits," Tusting tells SciDev.Net.

"The current WHO guidelines recommend that more evidence is needed before LSM can be recommended in certain settings. We provide evidence that, in some places, it could be used as an effective supplementary intervention," she adds.

The researchers stress that LSM should not be used alone, but only with control methods that target adult mosquitoes, such as using mosquito nets and spraying homes with insecticide.
Link to paper


Cochrane Database of Systematic Reviews doi: 10.1002/14651858.CD008923.pub2 (2013)