Abstract
BackgroundSub-microscopic (SM) Plasmodium infections represent transmission reservoirs that could jeopardise malaria elimination goals. A better understanding of the epidemiology of these infections and factors contributing to their occurrence will inform effective elimination strategies. While the epidemiology of SM P. falciparum infections has been documented, that of SM P. vivax infections has not been summarised. The objective of this study is to address this deficiency.Methodology/Principal FindingsA systematic search of PubMed was conducted, and results of both light microscopy (LM) and polymerase chain reaction (PCR)-based diagnostic tests for P. vivax from 44 cross-sectional surveys or screening studies of clinical malaria suspects were analysed. Analysis revealed that SM P. vivax is prevalent across different geographic areas with varying transmission intensities. On average, the prevalence of SM P. vivax in cross-sectional surveys was 10.9%, constituting 67.0% of all P. vivax infections detected by PCR. The relative proportion of SM P. vivax is significantly higher than that of the sympatric P. falciparum in these settings. A positive relationship exists between PCR and LM P. vivax prevalence, while there is a negative relationship between the proportion of SM P. vivax and the LM prevalence for P. vivax. Amongst clinical malaria suspects, however, SM P. vivax was not identified.Conclusions/SignificanceSM P. vivax is prevalent across different geographic areas, particularly areas with relatively low transmission intensity. Diagnostic tools with sensitivity greater than that of LM are required for detecting these infection reservoirs. In contrast, SM P. vivax is not prevalent in clinical malaria suspects, supporting the recommended use of quality LM and rapid diagnostic tests in clinical case management. These findings enable malaria control and elimination programs to estimate the prevalence and proportion of SM P. vivax infections in their settings, and develop appropriate elimination strategies to tackle SM P. vivax to interrupt transmission.
Highlights
The global malaria incidence and death rates have decreased in recent years [1] due to increasing funding and political commitment, as well as implementation of artemisinin combination therapy, better access to diagnostics and vector control interventions such as insecticide treated bed nets and indoor residual spray
The introduction of molecular based diagnostics such as polymerase chain reaction (PCR) in the 1990s resulted in increased reporting of Plasmodium infections in communities compared to Light microscopy (LM), indicating that sub-microscopic (SM) Plasmodium infections are endemic in a variety of different settings
The authors analysed LM and PCR results described in 38 publications (44 studies), and revealed that SM P. vivax is highly prevalent across different geographic areas with varying transmission intensities
Summary
The global malaria incidence and death rates have decreased in recent years [1] due to increasing funding and political commitment, as well as implementation of artemisinin combination therapy, better access to diagnostics and vector control interventions such as insecticide treated bed nets and indoor residual spray. Many countries/regions are planning or have already committed to eliminating malaria In these areas the malaria surveillance programs that generate information on malaria cases, burden and transmission trends need to be strengthened and extended to include case and foci investigations [2]. These focused investigations play a pivotal role in informing malaria elimination action plans and directing resources.
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