Background: Long-lasting insecticidal nets (LLINs) are the primary malaria prevention and control intervention in many parts of sub-Saharan Africa. While LLINs are expected to last at least 3 years under normal use conditions, they can lose effectiveness because they fall out of use, are discarded, repurposed, physically damaged, or lose insecticidal activity. The contributions of these different interrelated factors to durability of nets and their protection against malaria have been unclear. Methods: Starting in 2009, LLIN durability studies were conducted in seven countries in Africa over 5 years. WHOrecommended measures of attrition, LLIN use, insecticidal activity, and physical integrity were recorded for eight different net brands. These data were combined with analyses of experimental hut data on feeding inhibition and killing effects of LLINs on both susceptible and pyrethroid resistant malaria vectors to estimate the protection against malaria transmission-in terms of vectorial capacity (VC)-provided by each net cohort over time. Impact on VC was then compared in hypothetical scenarios where one durability outcome measure was set at the best possible level while keeping the others at the observed levels. Results: There was more variability in decay of protection over time by country than by net brand for three measures of durability (ratios of variance components 4.6, 4.4, and 1.8 times for LLIN survival, use, and integrity, respectively). In some countries, LLIN attrition was slow, but use declined rapidly. Non-use of LLINs generally had more effect on LLIN impact on VC than did attrition, hole formation, or insecticide loss. Conclusions: There is much more variation in LLIN durability among countries than among net brands. Low levels of use may have a larger impact on effectiveness than does variation in attrition or LLIN degradation. The estimated

BackgroundScaling-up of effective anti-malarial control strategies in Central-West region of Senegal has resulted in the sharp decline in malaria prevalence in this area. However, despite these strategies, residual malaria transmission has been observed in some villages (hot spots). The objective of this study was to assess the impact of indoor residual spraying (IRS) with pirimiphos-methyl on malaria transmission in hot spot areas.MethodsThe malaria vector population dynamics were monitored in each of the six selected villages (4 of which used IRS, 2 were unsprayed control areas) using overnight human landing catches (HLC) and pyrethrum spray catches (PSC). The host source of blood meals from freshly fed females collected using PSC was identified using the direct ELISA method. Females caught through HLC were tested by ELISA for the detection of Plasmodium falciparum circumsporozoite protein and Anopheles gambiae complex was identified using PCR.ResultsPreliminary data shown that the densities of Anopheles populations were significantly lower in the sprayed areas (179/702) compared to the control. Overall, malaria transmission risk was 14 times lower in the intervention zone (0.94) compared to the control zone (12.7). In the control areas, three Anopheles species belonging to the Gambiae complex (Anopheles arabiensis, Anopheles coluzzii and Anopheles melas) maintained the transmission, while only An. coluzzii was infective in the sprayed areas.ConclusionThe preliminary data from this pilot study showed that IRS with the CS formulation of pirimiphos-methyl is likely very effective in reducing malaria transmission risk. However, additional studies including further longitudinal entomological surveys as well as ecological and ethological and genetical characterization of vectors species and their populations are needed to better characterize the entomological impact of indoor residual spraying with pirimiphos-methyl in the residual transmission areas of Senegal.

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