LASR

The challenge

An estimated 250 million malaria infections occurred in 2022, most of them in sub-Saharan Africa. Despite this substantial burden of disease, there was a substantial improvement around the year 2000, with the prevalence of infection halved. Vector control is thought to have been the main cause of this decline, with the use of long-lasting insecticide-treated bed nets (LLINs) accounting for 68% of the decline and indoor insecticide spraying for 13%.

However, the decline in malaria has stalled over the past decade. Use of insecticides has led to concerns about environmental contamination and has driven the emergence of insecticide resistance in mosquitoes. LLINs are highly effective when used correctly, but can be uncomfortable, especially in hot weather, and there are indications that mosquito biting behaviour is changing, with feeding occurring outside the periods when people are protected by LLINs. 

As a result, there is a need for alternative passive control measures to complement LLINs and other interventions such as vaccination. One possible approach is the use of long-acting spatial repellents (LASRs) – chemicals that seem to reduce the likelihood of being bitten by mosquitoes and infected with malaria parasites. Although they are known to reduce the burden of malaria in communities,  their mode of action is not well understood and therefore requires further investigation to optimise vector control and inform policy decisions.

The project

The LASR project aims to generate high-quality evidence on the efficacy of a new long-acting spatial repellent (LASR) developed by SC Johnson, known as Guardian. It is also exploring the mode of action of Guardian to inform the development of next-generation products.

SC Johnson’s ‘Mosquito Shield’ product, which is active for about a month, has been shown to successfully reduce the burden of malaria disease. Additionally, their Guardian product is a significant advance, as it continues to have an effect for up to 12 months, allowing for once-yearly renewal of LASR devices. 

The LASR project is organising a clinical trial to compare the use of Guardian with another vector control strategy, indoor insecticide spraying with the commonly used insecticide pirimiphos-methyl, and with standard vector control. The studies will take place in a high-transmission area of Kenya, with vector control measures in addition to the standard malaria control measures typically deployed, such as LLINs and vaccination. Regular community surveys will be conducted to detect malaria infections in children, and hospital data on malaria cases will also be collected.

Alongside this trial, the project team will carry out a range of studies to provide insights into the effects of Guardian on mosquitoes. For example, high-speed video will be used to track mosquito flight behaviour near a model human in the presence of a LASR. In addition, effects on a model of blood feeding activity and parasite uptake will be compared in the presence and absence of a LASR. Effects on mosquito reproduction will also be assessed.

Impact

The LASR study will generate key evidence on a novel vector-control product. It will:

• Show whether the use of Guardian reduces the malaria disease burden and how its efficacy compares with indoor insecticide spraying.
• Assess community acceptability of Guardian and long-acting spatial repellents (LASRs) more generally.
• Generate insights into the potential mode of action of LASR, which would indicate what properties should be optimised in new product development. 

Vector control has proven benefits in reducing the burden of malaria. With insecticide spraying being phased out in multiple countries, the LASR study could lead to the registration of a new product that, alongside other measures, would protect children and adults against this feared disease.