Increased sensitivity of detecting variation in malaria endemicity by parasite density measurement in large surveys

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.