Abstract
BackgroundElimination of malaria can only be achieved through removal of all vectors or complete depletion of the infectious reservoir in humans. Mechanistic models can be built to synthesize diverse observations from the field collected under a variety of conditions and subsequently used to query the infectious reservoir in great detail.MethodsThe EMOD model of malaria transmission was calibrated to prevalence, incidence, asexual parasite density, gametocyte density, infection duration, and infectiousness data from nine study sites. The infectious reservoir was characterized by age and parasite detectability with diagnostics of varying sensitivity over a range of transmission intensities with and without case management and vector control. Mass screen-and-treat drug campaigns were tested for likelihood of achieving elimination.ResultsThe composition of the infectious reservoir is similar over a range of transmission intensities, and higher intensity settings are biased towards infections in children. Recent ramp-ups in case management and use of insecticide-treated bed nets (ITNs) reduce the infectious reservoir and shift the composition towards sub-microscopic infections. Mass campaigns with anti-malarial drugs are highly effective at interrupting transmission if deployed shortly after ITN campaigns.ConclusionsLow-density infections comprise a substantial portion of the infectious reservoir. Proper timing of vector control, seasonal variation in transmission intensity and mass drug campaigns allows lingering population immunity to help drive a region towards elimination.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0751-y) contains supplementary material, which is available to authorized users.
Highlights
Elimination of malaria can only be achieved through removal of all vectors or complete depletion of the infectious reservoir in humans
Measurements of average annual parasite prevalence from endemic areas predict infections to last longer than is observed in malariatherapy patients. It is possible the model is operating in a sub-optimal regime of P. falciparum antigenic variants for reasonable predictions of the infectious reservoir at entomological inoculation rates (EIRs) = 0.1, as strain diversity can be much lower in lowtransmission settings [39]
rapid diagnostic tests (RDT)-negative infections make up a substantial portion of the infectious reservoir over a wide range of transmission intensities
Summary
Elimination of malaria can only be achieved through removal of all vectors or complete depletion of the infectious reservoir in humans. Many regions have made considerable progress in malaria control and are working towards local elimination of malaria [2, 3]. Technical strategies for elimination differ from those for control, and it is critical to understand the factors that lead to successful outcomes and make the best use of available resources. Complete depletion of the infectious reservoir of malaria parasites requires clearing all malaria infections in both human and vector populations. In regions where malaria is endemic, accumulated exposure to infection leads individuals to develop immunity to clinical symptoms and partial immunity to parasites. Proper identification of parasite carriers is confounded by a population of asymptomatic people with low-density infections
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