Mapping the global prevalence, incidence, and mortality of Plasmodium falciparum, 2000-17: a spatial and temporal modelling study

Abstract

Background: Since 2000, the scale-up of malaria control interventions has substantially reduced morbidity and mortality caused by the disease globally, fuelling bold aims for disease elimination. In tandem with increased availability of geospatially resolved data, malaria control programmes increasingly use high-resolution maps to characterise spatially heterogeneous patterns of disease risk and thus efficiently target areas of high burden.

Methods: We updated and refined the Plasmodium falciparum parasite rate and clinical incidence models for sub-Saharan Africa, which rely on cross-sectional survey data for parasite rate and intervention coverage. For malaria endemic countries outside of sub-Saharan Africa, we produced estimates of parasite rate and incidence by applying an ecological downscaling approach to malaria incidence data acquired via routine surveillance. Mortality estimates were derived by linking incidence to systematically derived vital registration and verbal autopsy data. Informed by high-resolution covariate surfaces, we estimated P falciparum parasite rate, clinical incidence, and mortality at national, subnational, and 5 × 5 km pixel scales with corresponding uncertainty metrics.

Findings: We present the first global, high-resolution map of P falciparum malaria mortality and the first global prevalence and incidence maps since 2010. These results are combined with those for Plasmodium vivax (published separately) to form the malaria estimates for the Global Burden of Disease 2017 study. The P falciparum estimates span the period 2000-17, and illustrate the rapid decline in burden between 2005 and 2017, with incidence declining by 27·9% and mortality declining by 42·5%. Despite a growing population in endemic regions, P falciparum cases declined between 2005 and 2017, from 232·3 million (95% uncertainty interval 198·8-277·7) to 193·9 million (156·6-240·2) and deaths declined from 925 800 (596 900-1 341 100) to 618 700 (368 600-952 200). Despite the declines in burden, 90·1% of people within sub-Saharan Africa continue to reside in endemic areas, and this region accounted for 79·4% of cases and 87·6% of deaths in 2017.

Interpretation: High-resolution maps of P falciparum provide a contemporary resource for informing global policy and malaria control planning, programme implementation, and monitoring initiatives. Amid progress in reducing global malaria burden, areas where incidence trends have plateaued or increased in the past 5 years underscore the fragility of hard-won gains against malaria. Efforts towards elimination should be strengthened in such areas, and those where burden remained high throughout the study period.

Funding: Bill & Melinda Gates Foundation.

Figure 1

Plasmodium falciparum incidence (A and B) and count (C and D) globally and for sub-Saharan Africa from 2000–17 95% uncertainty intervals shown via the corresponding coloured bands around the mean lines. Rates were calculated using the total population in each age group in all endemic countries.

Figure 2

Regional distribution of Plasmodium falciparum incidence (A) and count (B) To show trends across regions with such different endemicity levels, the y-axis is scaled using the square root of incidence (per 1000 individuals) for A and count (in millions of cases) for B. 95% uncertainty intervals are shown via the corresponding coloured bands behind the mean lines. Rates were calculated using the total population in all endemic countries within each region.

Figure 3

Spatial distribution of age-standardised P falciparum parasite rate_2–10 in 2005 (top) and 2017 (bottom) Note the colour scaling is split to better differentiate within low endemic areas, with one linear scale between zero and 0·01 P falciparum parasite rate_2–10 (grey shades) and a second linear scale between 0·01 and 1 (colours from blue to red). Areas without endemic P falciparum are shown in white. P falciparum parasite rate_2–10=P falciparum parasite rate for children aged 2–10 years of age.

Figure 4

Spatial distribution of all-age Plasmodium falciparum incidence in 2005 (top) and 2017 (bottom) Note the colour scaling is split to better differentiate within low endemic areas, with one linear scale between rates of zero and 10 (grey shades) and a second linear scale between 10 and 1000 (colours from purple to yellow). Areas without endemic P falciparum are shown in white.

Figure 5

Spatial distribution of all-age Plasmodium falciparum mortality (deaths per 100 000 population per annum) in 2005 (top) and 2017 (bottom)