Insecticide treated eave nets and window screens for malaria control
Lead Research Organisation:
London School of Hygiene & Tropical Medicine
Department Name: Epidemiology and Population Health
Abstract
Long lasting insecticidal nets (LLIN) are a key component of malaria control and are responsible for saving many lives; but they have several drawbacks. About half of people living in malaria endemic areas do not have access to LLINs. Some of this deficit is due to insufficient delivery of nets, but a major factor is LLINS becoming rapidly damaged, resulting in a lifespan less than their intended 3-years. Additionally, there is typically an unequal distribution of nets to certain groups within households. For example, while the youngest children and their mothers are likely to sleep under nets, school age children often have very low access to nets. And even those who do have access to nets are only protected when they are sleeping.
We propose a new tool - purpose made insecticide-treated eave nets (ITENs) with insecticide treated window screens (ITWS) for full house screening. ITENs are purpose made netting rolls that are applied to the house under the overhang of the roof and across windows within 30 minutes by local teams using hammer and nails. These interventions have at least three potential advantages over LLINs: they protect everybody in the household; they protect them at all times when they are in the household; and the are potentially much more durable than LLINs, giving up to 5 years' protection and making them highly cost effective (up to $1.75 per year per household less than LLINs). ITENs fixed across the eaves of household structures and ITWS on the windows block access to and kill Anopheles mosquitoes at their main access points into houses. Mosquitoes are attracted to houses, try to enter through the eaves or windows, and will come up against insecticides in the interventions, turning the house into a "lure and kill", that not only protect people in the house but also everyone in the community. Preliminary household randomised evaluation of ITENs and ITWS among 80 households in Western Kenya in 2012-14 showed 75% fewer vector mosquitoes in the houses using ITENs, ITWS and LLINs when compared to households using LLINs only. ITENs and ITWS are already available and scalable and can be fitted to any type of house.
ITENs and ITWS have advantages over LLINs for the application of insecticides. LLINS are touched daily and washed regularly, limiting the range of chemicals which can be applied. ITENs and ITWS are compatible with a wider range of insecticides. This will be greatly advantageous because insecticides used for malaria control are becoming less effective in Africa due to the growing resistance of mosquitoes - and particularly because resistance is a local phenomenon: chemicals that work in one place may be ineffective in another so it is vital to have a wide choice of insecticides. In addition, ITENs and ITWS can be made from denser, more durable material. This not only makes them more physically durable but allows a greater quantity of insecticide to be impregnated, killing more mosquitoes, even resistant ones, and making the effect last longer.
We propose in due course to undertake a large-scale cluster randomised trial with epidemiological endpoints in Tanzania. However, before this is possible it is necessary to investigate which particular combination of insecticides, is appropriate to the local conditions. We also wish to undertake a study to assess how feasible it is to fit ITENs and ITWS to local houses and how acceptable local communities find them. We are therefore applying for a development grant for a 2 small preliminary studies: one in experimental huts, which will be conducted to compare the household and community protective efficacy of 2 ITEN and ITWS products with different insecticides in local conditions to see which is better to take forward to a large scale trial; and a second in which 200 local houses are fitted with ITENs and ITWS and followed up after 1 year to assess ease and cost of fitting, longevity and community acceptability.
We propose a new tool - purpose made insecticide-treated eave nets (ITENs) with insecticide treated window screens (ITWS) for full house screening. ITENs are purpose made netting rolls that are applied to the house under the overhang of the roof and across windows within 30 minutes by local teams using hammer and nails. These interventions have at least three potential advantages over LLINs: they protect everybody in the household; they protect them at all times when they are in the household; and the are potentially much more durable than LLINs, giving up to 5 years' protection and making them highly cost effective (up to $1.75 per year per household less than LLINs). ITENs fixed across the eaves of household structures and ITWS on the windows block access to and kill Anopheles mosquitoes at their main access points into houses. Mosquitoes are attracted to houses, try to enter through the eaves or windows, and will come up against insecticides in the interventions, turning the house into a "lure and kill", that not only protect people in the house but also everyone in the community. Preliminary household randomised evaluation of ITENs and ITWS among 80 households in Western Kenya in 2012-14 showed 75% fewer vector mosquitoes in the houses using ITENs, ITWS and LLINs when compared to households using LLINs only. ITENs and ITWS are already available and scalable and can be fitted to any type of house.
ITENs and ITWS have advantages over LLINs for the application of insecticides. LLINS are touched daily and washed regularly, limiting the range of chemicals which can be applied. ITENs and ITWS are compatible with a wider range of insecticides. This will be greatly advantageous because insecticides used for malaria control are becoming less effective in Africa due to the growing resistance of mosquitoes - and particularly because resistance is a local phenomenon: chemicals that work in one place may be ineffective in another so it is vital to have a wide choice of insecticides. In addition, ITENs and ITWS can be made from denser, more durable material. This not only makes them more physically durable but allows a greater quantity of insecticide to be impregnated, killing more mosquitoes, even resistant ones, and making the effect last longer.
We propose in due course to undertake a large-scale cluster randomised trial with epidemiological endpoints in Tanzania. However, before this is possible it is necessary to investigate which particular combination of insecticides, is appropriate to the local conditions. We also wish to undertake a study to assess how feasible it is to fit ITENs and ITWS to local houses and how acceptable local communities find them. We are therefore applying for a development grant for a 2 small preliminary studies: one in experimental huts, which will be conducted to compare the household and community protective efficacy of 2 ITEN and ITWS products with different insecticides in local conditions to see which is better to take forward to a large scale trial; and a second in which 200 local houses are fitted with ITENs and ITWS and followed up after 1 year to assess ease and cost of fitting, longevity and community acceptability.
Technical Summary
We will conduct an efficacy study of 2 ITENs and ITWS against local mosquitoes. We will use the Ifakara semi-field site, comprising 4 experimental huts, each in its own enclosure. Volunteers sleep in the huts and mosquitoes are introduced into the enclosures. The following morning, the mosquitoes are assessed in terms of mortality, blood feeding and hut entry. The two ITENs to be tested are 1) the insecticide deltamethrin together with the synergist piperonyl butoxide PBO 2) the insecticide clothianidin; both of which are effective against resistant mosquitoes. The other 2 huts will be controls: one will be a negative control with no insecticidal intervention to ensure experimental validity; in the other, the sleeper will use a LLIN treated with deltamethrin and (PBO) for comparison with the standard of care. An experiment will last 4 weeks. In the first week, each of the huts will be randomly assigned to one of the 4 arms. For 4 nights, 60 (30 anopheles and 30 aedes) mosquitoes will be released into each enclosure each night and the outcomes will be recorded the following morning. Then the 4 interventions will be rotated between the 4 huts in a Latin square design and after 3 nights' washout the procedure will be repeated until each intervention has been in each hut. During the 4 nights each week, the sleepers will be rotated between huts. The experiment will be done 6 times, with new ITENs and ITWS then with artificially aged ones to approximate 1, 2, 3, 4 and 5 years of field use.
We will conduct a second study on feasibility and acceptability. We will put up ITENs and ITWS in 200 houses in local villages to demonstrate that they can easily fitted and learn lessons of how to do this in the local environment. At baseline, we will conduct a survey on acceptability and attitudes to the products. We will follow up 1 year later and ask acceptability. In the one year survey we will assess the proportion of products still in place, and the condition of the products.
We will conduct a second study on feasibility and acceptability. We will put up ITENs and ITWS in 200 houses in local villages to demonstrate that they can easily fitted and learn lessons of how to do this in the local environment. At baseline, we will conduct a survey on acceptability and attitudes to the products. We will follow up 1 year later and ask acceptability. In the one year survey we will assess the proportion of products still in place, and the condition of the products.
Planned Impact
This trial development grant would allow us to plan for a future cluster randomised trial of ITENs and ITWS with epidemiological outcomes. Specifically, it would allow us to select the most appropriate insecticidal products to use against local vectors with resistance to insecticides, allow us to assess the ease of fitting the products to local houses and refine our methods for doing so, and give us data on acceptability of the products to local populations and how acceptability might be improved in the future.
Demonstrating the effectiveness of ITENs and ITWS would bring many benefits for malaria control. ITENs and ITWS have the potential to be long lasting, cost effective, protect everybody in the household at all times when they are indoors and require less compliance from the user than LLINs. ITENs and ITWS are good candidates for deployment of new insecticides as they are not washed or in daily contact with skin and the fast knockdown characteristic of pyrethroids may not be required. This may offer great advantages insecticide resistance management. Further more, ITENs and ITWS are likely to me more cost effective than LLINs or indoor residual spraying.
There may also be an economic boost to low income countries that use ITENs and ITWS. Approximately 85% of the jobs associated with LLIN production are in cutting and sewing activities (fabric to finished LLIN). Since the material for ITENs and ITWS is sent on rolls and installation occurs at the site of implementation, there is a transfer of employment from the manufacturing site to the program country.
Demonstrating the effectiveness of ITENs and ITWS would bring many benefits for malaria control. ITENs and ITWS have the potential to be long lasting, cost effective, protect everybody in the household at all times when they are indoors and require less compliance from the user than LLINs. ITENs and ITWS are good candidates for deployment of new insecticides as they are not washed or in daily contact with skin and the fast knockdown characteristic of pyrethroids may not be required. This may offer great advantages insecticide resistance management. Further more, ITENs and ITWS are likely to me more cost effective than LLINs or indoor residual spraying.
There may also be an economic boost to low income countries that use ITENs and ITWS. Approximately 85% of the jobs associated with LLIN production are in cutting and sewing activities (fabric to finished LLIN). Since the material for ITENs and ITWS is sent on rolls and installation occurs at the site of implementation, there is a transfer of employment from the manufacturing site to the program country.
