Abstract
Insecticide-treated nets (ITNs) are among the three major intervention measures that have reduced malaria transmission in the past decade. However, increased insecticide resistance in vectors, together with outdoor transmission, has limited the efficacy of the ITN scaling-up efforts. Observations on longitudinal changes in ITN coverage and its impact on malaria transmission allow policy makers to make informed adjustments to control strategies. We analyzed field surveys on ITN ownership, malaria parasite prevalence, and malaria vector population dynamics in seven sentinel sites in western Kenya from 2003 to 2015. We found that ITN ownership has increased from an average of 18% in 2003 to 85% in 2015. Malaria parasite prevalence in school children decreased by about 70% from 2003 to 2008 (the first mass distribution of free ITNs was in 2006) but has resurged by >50% since then. At the community level, use of ITNs reduced infections by 23% in 2008 and 43% in 2010, although the reduction was down to 25% in 2011. The indoor-resting density of the predominant vector, Anopheles gambiae, has been suppressed since 2007; however, Anopheles funestus populations have resurged and have increased 20-fold in some places since 2007. In conclusion, there is limited room for further increase in ITN coverage in western Kenya. The rebounding in malaria transmission highlights the urgent need of new or improved malaria control interventions so as to further reduce malaria transmission.
Highlights
The scale-up of interventions, including insecticide-treated nets (ITNs), indoor residual sprays (IRS), and artemisinin-based combination therapy (ACT), has led to a significant reduction in malaria morbidity and mortality in the past decade [1]
No study has looked into the effectiveness of Insecticide-treated nets (ITNs) over time to compare the impact of ITNs on malaria transmission at different periods – e.g., before or immediately after the first mass ITN campaign in 2006 compared with about 10 years later
ITN ownership has decreased by about 4% in Iguhu from 2012 to 2015 (Figure 2)
Summary
The scale-up of interventions, including insecticide-treated nets (ITNs), indoor residual sprays (IRS), and artemisinin-based combination therapy (ACT), has led to a significant reduction in malaria morbidity and mortality in the past decade [1]. Possible risk factors limiting the effectiveness of ITNs have been explored, including vector insecticide resistance, outdoor transmission, vector species shifting, vectors biting animals, insecticide decay, and the varying integrity of LLINs under different conditions of use [14, 18, 25, 27, 28]. No study has looked into the effectiveness of ITNs over time to compare the impact of ITNs on malaria transmission at different periods – e.g., before or immediately after the first mass ITN campaign in 2006 compared with about 10 years later. This knowledge would be valuable to malaria control programs as they plan for procurement and replacement
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