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. 2013;10(6):e1001467.
doi: 10.1371/journal.pmed.1001467. Epub 2013 Jun 18.

Targeting asymptomatic malaria infections: active surveillance in control and elimination

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Targeting asymptomatic malaria infections: active surveillance in control and elimination

Hugh J W Sturrock et al. PLoS Med. 2013.

Abstract

Hugh Sturrock and colleagues discuss the role of active case detection in low malaria transmission settings. They argue that the evidence for its effectiveness is sparse and that targeted mass drug administration should be evaluated as an alternative or addition to active case detection.

Please see later in the article for the Editors' Summary

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Microepidemiology of malaria in villages of varying transmission setting.
In moderate/high transmission settings (A), hotspots coalesce to form a more homogeneous pattern. In lower transmission settings (B), risk becomes increasingly spatially discrete, with single households or small groups of households experiencing higher exposure. In very low transmission settings (C), risk shifts to individual households or, where transmission is occurring outside the house/village, to individuals.
Figure 2
Figure 2. Illustration of hotpops (hot populations).
While infection may be detected in individuals at their home, they acquire their infections elsewhere. For example, individuals may be exposed to infectious mosquitoes when working in particular forests overnight (e.g., rubber tappers); when camping in the forest due to occupation (e.g., loggers, miners, and military personnel); or in their place of origin (migrant laborers). These demographic groups are at high risk of infection and can seed malaria transmission to others in receptive areas.
Figure 3
Figure 3. Potential application of different active surveillance and mass drug administration approaches to reduce transmission.
Due to the resource requirements of tracing cases back to their home, reaction case detection (RACD) is best suited to lower transmission settings. Similarly, to avoid large amounts of unnecessary treatments, mass drug administration (MDA) is better suited to higher transmission settings; lower transmission areas may benefit from a more targeted approach. Where risk factors are well defined, proactive case detection (PACD) and MDA are good options. RACD and targeted mass drug administration (tMDA) are useful where risk factors are not well defined, as passively or actively detected cases can be used to identify at-risk populations. Where the proportion of asymptomatic infections is high, passive surveillance does not suffice and additional active surveillance and presumptive treatment are required. Where the proportion of sub-patent infections is high, active surveillance using current diagnostics is less likely to impact transmission, and presumptive treatment (MDA or tMDA) should therefore be considered.

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