ArticlesCombination of malaria vector control interventions in pyrethroid resistance area in Benin: a cluster randomised controlled trial
Introduction
Despite substantial efforts and increasing international funding dedicated throughout the world to control and eliminate malaria,1 the disease is still a major public health issue with nearly 216 million cases a year and about 655 000 deaths, 86% of whom are children younger than 5 years.2 Recommendations of the World Health Organization (WHO Global Malaria Programme-Roll Back Malaria [RBM] Partnership) to combat malaria include artemisinin-based combination therapy and long-lasting insecticidal nets (LLIN), supported by indoor residual spraying of insecticide (IRS) and intermittent preventive treatment during pregnancy. Between 2008 and 2010, nearly 289 million insecticide-treated mosquito nets were delivered to sub-Saharan Africa, enough to protect 578 million people. Additionally, about 81 million people, representing 11% of the population at risk, were also protected by IRS.2 Deployment of such strategies has shown important reduction in malaria-associated morbidity and mortality in settings with moderate-to-high transmission levels in sub-Saharan Africa,3, 4 but a recent increase of malaria cases was reported in some African countries, hence underlining the fragility of malaria prevention and control in this part of the world.2, 5
The overarching goal of malaria vector control is to decrease the vectorial capacity of local vector populations below the critical threshold needed to achieve a malaria reproduction number (R0, the expected number of human cases that arise from each human case in a population) of less than one. Unfortunately, current methods (LLIN and IRS) are highly dependent on a single class of insecticides, the pyrethroids, for which malaria vectors have developed various resistance mechanisms.6 To ensure the success of vector control efforts and malaria elimination in Africa, the WHO-RBM and Malaria Eradication Research Agenda (malERA) consultative vector control group emphasised the need to search for innovative strategies. These strategies should aim at more effective control of pyrethroid-resistant malaria vectors to strongly decrease and interrupt disease transmission in endemic areas.7, 8
In some countries where more resources have become available, malaria control programmes have recently deployed both IRS and LLIN in the same malaria risk areas.2 The aims of this combined approach are to reduce transmission—and hence the malaria burden—more rapidly than might be feasible with one method alone and to delay the emergence of insecticide resistance by use of different classes of insecticide for IRS and LLINs. So far, a small number of studies9, 10 and mathematical modelling exercises11, 12 suggest that such combination has an added benefit for reduction of the risk of infection because the people not protected by one of the interventions are protected by the other. However, all the available studies were observational (ie, non experimental, without randomised allocation of the interventions), and in none of them could confounding factors be entirely excluded. Despite the great interest in combining methods for malaria control and elimination, no evidence exists for an epidemiological effect of LLIN and IRS, which we define here as the implementation of both interventions at the same time, in the same community, and against the same vector population.
The aim of this study was to investigate whether the use of both interventions in combination (ie, LLIN plus IRS or LLIN plus carbamate-treated plastic sheeting [CTPS]) afforded enhanced protection against clinical malaria at community level and a better management of pyrethroid-resistance in malaria vectors than did a selective coverage of LLIN in children younger than 6 years (reference group according to recommendations by the National Malaria Control Programme [NMCP]). The rationale behind the use of CTPS came from results of preliminary experimental hut studies in west Africa that showed good insecticidal activity of CTPS against pyrethroid-resistant malaria vectors.13, 14 The trial also aimed at determining whether universal coverage of LLIN could afford better protection against malaria than would selective coverage by achieving a mass killing effect.15 The assumption is that much more reduction of transmission is expected with universal coverage of all sleeping units with LLIN (ULLIN) because of a reduction of the infection rate of vectors by poor access to the largest part of the human population that is infected (oldest children and adults) and the shortening of the life expectancy of the vectors.
Section snippets
Study design
We did a cluster randomised controlled trial in the health district of Ouidah-Kpomassè-Tori Bossito (OKT), southern Benin, between June 23, 2008, and Dec 24, 2009. The inclusion criteria for villages were moderate level of pyrethroid resistance in malaria vectors (kdr allelic frequency <40%), minimum distance of 2 km between villages, population size of 250–500 inhabitants with non-isolated habitations, and absence of a local health centre. Inclusion criteria for children were age (0–71 months)
Results
Of the 58 villages screened, 28 were enrolled and randomly assigned to vector control intervention (TLLIN, ULLIN, TLLIN+IRS, and ULLIN+CTPS; figure 1). Between 651 and 920 children were assessed for eligibility in every group and 40–60% of them were randomised (figure 2). A total of 16 327 blood thick films were analysed (about 4000 in each group). In every group, about 20% of the recordings were not taken into account because of loss to follow-up (17%), death of children (1·5%), and refusal
Discussion
We investigated the efficacy of new vector control strategies for malaria control and whether the use of combined interventions (ie, LLIN+IRS or LLIN+CTPS) would reduce malaria morbidity and transmission and allow better management of pyrethroid-resistance in malaria vectors relative to a background of LLIN coverage. Overall, however, neither clinical malaria nor the prevalence of infection and parasite density of asymptomatic infection in children younger than 6 years were reduced in southern
References (40)
- et al.
Malaria: 2 years in the fast lane
Lancet
(2009) - et al.
Malaria morbidity and pyrethroid resistance after the introduction of insecticide-treated bednets and artemisinin-based combination therapies: a longitudinal study
Lancet Infect Dis
(2011) - et al.
Pyrethroid resistance in African anopheline mosquitoes: what are the implications for malaria control?
Trends Parasitol
(2011) World Malaria Report 2011. Geneva, Switzerland: World Health Organization, 2011
- et al.
Indoor residual spraying for preventing malaria
Cochrane Database Syst Rev
(2010) Insecticide-treated bed nets and curtains for preventing malaria
Cochrane Database Syst Rev
(2004)Global Malaria Action Plan World Health Organization; 2009
(2009)A research agenda for malaria eradication: vector control
PLoS Med
(2011)- et al.
Combining indoor residual spraying and insecticide-treated net interventions
Am J Trop Med Hyg
(2009) - et al.
Combining indoor residual spraying and insecticide-treated nets for malaria control in Africa: a review of possible outcomes and an outline of suggestions for the future
Malar J
(2011)
Comparing the effectiveness of malaria vector-control interventions through a mathematical model
Am J Trop Med Hyg
Modelling the impact of vector control interventions on Anopheles gambiae population dynamics
Parasit Vectors
Managing insecticide resistance in malaria vectors by combining carbamate-treated plastic wall sheeting and pyrethroid-treated bed nets
Malar J
Indoor use of plastic sheeting impregnated with carbamate combined with long-lasting insecticidal mosquito nets for the control of pyrethroid-resistant malaria vectors
Am J Trop Med Hyg
Community-wide effects of permethrin-treated bed nets on child mortality and malaria morbidity in western Kenya
Am J Trop Med Hyg
Technical updates of the guidelines on the Integrated Management of Childhood illness (IMCI)
Guidelines for testing mosquito adulticides intended for indoor residual spraying (IRS) and insecticide treated nets (ITNs)
Malaria infection and disease in an area with pyrethroid-resistant vectors in southern Benin
Malar J
Cited by (157)
Increasing challenges of malaria control in sub-Saharan Africa: Priorities for public health research and policymakers
2022, Annals of Medicine and SurgerySystematic review of the entomological impact of insecticide-treated nets evaluated using experimental hut trials in Africa
2021, Current Research in Parasitology and Vector-Borne DiseasesCitation Excerpt :The review also identified that very few trials investigated the use of IRS in combination with ITNs, and none that showed the impact over a long time-period as insecticide decayed on the walls. The added benefit of this combination of vector control tools is unclear, with varying results found in RCTs (Protopopoff et al., 2007; Kleinschmidt et al., 2009; Corbel et al., 2012). These analyses present EHT predictions for the changes to the entomological efficacy of pyrethroid-only ITNs used against mosquito populations with increasing levels of pyrethroid resistance.
Biolarviciding for malaria vector control: Acceptance and associated factors in southern Tanzania
2021, Current Research in Parasitology and Vector-Borne DiseasesCitation Excerpt :Strategies to control the disease involve adoption of integrated vector control methods that mainly involve the use of techniques that target adult mosquitoes such as long-lasting insecticide-treated bed nets and indoor residual spraying (Musoke et al., 2018). However, these methods are challenged by mosquito development of resistance to the commonly used insecticides and changes in biting behaviors (Corbel et al., 2012; Walker et al., 2016; Choi and Furnival-Adams, 2019). The WHO recommends countries to engage in additional control techniques that avoid use of insecticides, or those used for adult control, such as environmental modification, manipulation and biological control, e.g. biolarviciding, depending on suitability in local contexts (WHO, 2013).
Semi-field evaluation of bacterial bio-pesticide Streptomyces indiaensis (LMG19961) susceptibility against Dengue Vector: Aedes aegypti (L.)
2024, International Journal of Tropical Insect Science
- †
These authors contributed equally