Abstract
.In areas of seasonal malaria transmission, the incidence rate of malaria infection is presumed to be near zero at the end of the dry season. Asymptomatic individuals may constitute a major parasite reservoir during this time. We conducted a longitudinal analysis of the spatio-temporal distribution of clinical malaria and asymptomatic parasitemia over time in a Malian town to highlight these malaria transmission dynamics. For a cohort of 300 rural children followed over 2009–2014, periodicity and phase shift between malaria and rainfall were determined by spectral analysis. Spatial risk clusters of clinical episodes or carriage were identified. A nested-case-control study was conducted to assess the parasite carriage factors. Malaria infection persisted over the entire year with seasonal peaks. High transmission periods began 2–3 months after the rains began. A cluster with a low risk of clinical malaria in the town center persisted in high and low transmission periods. Throughout 2009–2014, cluster locations did not vary from year to year. Asymptomatic and gametocyte carriage were persistent, even during low transmission periods. For high transmission periods, the ratio of asymptomatic to clinical cases was approximately 0.5, but was five times higher during low transmission periods. Clinical episodes at previous high transmission periods were a protective factor for asymptomatic carriage, but carrying parasites without symptoms at a previous high transmission period was a risk factor for asymptomatic carriage. Stable malaria transmission was associated with sustained asymptomatic carriage during dry seasons. Control strategies should target persistent low-level parasitemia clusters to interrupt transmission.
Highlights
IntroductionIn Mali, malaria control strategies have included artemisinin-based combination therapy (ACT), widespread distribution of free long-lasting insecticide-treated nets (ITNs), diagnosis with free rapid diagnosis tests (RDTs), and free medical care of children up to 5 years of age with uncomplicated or severe malaria
In the Sahel, where malaria transmission is seasonal, control programs aim to interrupt transmission or at least decrease malaria burden, demonstrating efficacy in several regions.[1,2,3,4] These programs include deployment of rapid diagnosis tests (RDTs) and artemisinin-based combination therapy (ACT), the widespread distribution of insecticide-treated nets (ITNs), indoor residual spraying, intermittent preventive treatment (IPT) of pregnant women, and seasonal malaria chemoprophylaxis (SMC).In Mali, malaria control strategies have included ACTs, widespread distribution of free long-lasting ITNs, diagnosis with free RDTs, and free medical care of children up to 5 years of age with uncomplicated or severe malaria
We conducted a longitudinal analysis of the spatio-temporal distribution of clinical malaria and asymptomatic parasitemia over time in a Malian town to highlight these malaria transmission dynamics
Summary
In Mali, malaria control strategies have included ACTs, widespread distribution of free long-lasting ITNs, diagnosis with free RDTs, and free medical care of children up to 5 years of age with uncomplicated or severe malaria. The high incidence of malaria in this rural area persists despite a 6-month dry season. In Sudan and Senegal, asymptomatic carriers of Plasmodium are present throughout the low transmission period.[6,7] Long-term parasite carriage may be critical for parasite survival, and these infected individuals may constitute a major reservoir when environmental conditions are not favorable for mosquito development.[8] even in endemic areas, malaria transmission is not uniformly distributed; it can be patchy and dependent on factors, such as location of mosquito breeding sites and areas of clustered human habitations, which act as reservoirs of parasites.[9,10] The persistence of malaria transmission in “hotspots,” such as a household or cluster of households may help the parasite to survive during the dry season.[10,11,12] Strategies for detecting and targeting these hotspots, whether geographic or demographic, are important to reduce the local parasite reservoir and interrupting transmission.[13]
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