Mapping multiple components of malaria risk for improved targeting of elimination interventions

Abstract

There is a long history of considering the constituent components of malaria risk and the malaria transmission cycle via the use of mathematical models, yet strategic planning in endemic countries tends not to take full advantage of available disease intelligence to tailor interventions. National malaria programmes typically make operational decisions about where to implement vector control and surveillance activities based upon simple categorizations of annual parasite incidence. With technological advances, an enormous opportunity exists to better target specific malaria interventions to the places where they will have greatest impact by mapping and evaluating metrics related to a variety of risk components, each of which describes a different facet of the transmission cycle. Here, these components and their implications for operational decision-making are reviewed. For each component, related mappable malaria metrics are also described which may be measured and evaluated by malaria programmes seeking to better understand the determinants of malaria risk. Implementing tailored programmes based on knowledge of the heterogeneous distribution of the drivers of malaria transmission rather than only consideration of traditional metrics such as case incidence has the potential to result in substantial improvements in decision-making. As programmes improve their ability to prioritize their available tools to the places where evidence suggests they will be most effective, elimination aspirations may become increasingly feasible.

Keywords: Epidemiology; Health policy; Malaria; Operational planning; Risk mapping.

Fig. 1

Components of malaria risk and relationships between them. Malaria risk can be considered as the combination of epidemiological factors typically measured programmatically (yellow boxes), factors influencing transmission rates (blue boxes), and measures of transmission potential or intensity (green boxes). Incident infections acquired both locally or imported replenish the parasite reservoir, with parasites persisting according to the human infection duration. The transmission intensity, which generates new local incidence, is determined by the combination of the human parasite reservoir and the entomological potential for transmission of that reservoir. Together, the mosquito-related entomological potential and the human-related infection duration largely comprise the transmission potential of a place, which describes the risk of malaria propagating there even if no parasites are currently circulating. Red boxes illustrate the interventions that reduce specific risk components