Increased sensitivity of detecting variation in malaria endemicity by parasite density measurement in large surveys
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Introduction
The continuing high and inequitable global malaria burden requires improved methods to understand trends and target control. Current methods often involve infection prevalence surveys, but additional parasitological measures could increase precision in estimating infection burdens of communities.
Methods
Focusing on the country with most malaria globally, examinations of slides from 10,651 children under five sampled in the 2021 national Malaria Indicator Survey in Nigeria were performed to measure asexual parasite densities in infected children and discriminate sexual stages and species. Variation in these indices among the six different geopolitical zones and 37 individual states including the Federal Capital Territory were compared with the variation indicated by infection prevalence alone.
Results
Among the six major geopolitical zones, only one had significantly higher asexual parasite prevalence than others, but parasite densities within infected children revealed more significant variation among the different zones. Comparing results for 2021 with previous data from 2018, one zone showed lower asexual parasite prevalence and two had lower sexual parasite prevalence, but three had higher asexual parasite densities in infected children. Variation in parasite densities among individual states also highlighted significant geographical and temporal differences, extending the detection of heterogeneity within each geopolitical zone. Overall trends were driven by the predominant parasite species Plasmodium falciparum as prevalence and density of the other species were much lower.
Conclusions
Findings indicate that understanding complex patterns of geographical and temporal variation is enhanced by including asexual parasite density measurement, providing opportunities for more precise targeting of malaria control within high burden countries.
Key Messages of Article
What is already known on this topic
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Heterogeneity in malaria infection burden among endemic communities is commonly assessed by surveying parasite prevalence.
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Previous analysis of blood stage malaria parasite densities suggested that incorporation of this variable might contribute to a more thorough assessment.
What this study adds
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Analysis of the 2021 national survey in Nigeria shows that incorporation of parasite density data enhances detection of heterogeneity, among major geopolitical zones and individual states.
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Comparison with 2018 data identifies variation over time more sensitively, with some communities showing an increase and others a decrease in infection burden.
How this study might affect research, practice or policy
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Given only marginal extra resources needed to obtain the additional microscopy measurements, on top of scoring parasite positivity, these may be recommended to enhance monitoring and targeting of malaria control.
