High-resolution maps of Plasmodium falciparum malaria inform where malaria elimination efforts should be strengthened by highlighting where burden remains high, according to study results published in The Lancet.
Although P falciparum malaria has substantially declined globally since 2000, in areas of high burden persist in many countries. This global decline is a result of the scale-up of malaria control interventions that have greatly reduced mortality and morbidity. Establishing the spatiotemporal patterns in global malaria maps is necessary to contextualize changes in burden relative to shifting disease control policy, funding, and implementation.
However, previous global maps have focused on a single year and did not include routine surveillance data for modeling burden. By combining the survey-derived parasite rate and health system-derived case incidence data for P falciparum, burden estimates can be compared globally. Therefore, this study generated the first-ever, high-resolution, temporally dynamic, global maps of P falciparum incidence, prevalence, and mortality in 106 endemic countries from 2000 to 2017.
Parasite rate and clinical incidence models for sub-Saharan Africa, which rely on cross-sectional survey data, were updated and refined. Estimates of parasite rate and clinical incidence for endemic countries outside of sub-Saharan Africa were produced by applying an ecological downscaling approach to malaria incidence data that was acquired via routine surveillance. Mortality estimates were derived by linking incidence to systemically derived vital registration and verbal autopsy data. The P falciparum parasite rate, clinical incidence, and mortality were estimated in national, subnational, and 5×5 km pixel scales with corresponding uncertainty metrics.
To form malaria estimates for the Global Burden of Disease 2017 study, results for illness associated with P falciparum were combined with those for P vivax, which were published separately. The incidence per 100,000 declined from 35.7 in 2000 to 26.3 and mortality per 100,000 declinedfrom 14.3 to 8.4, thus, estimates for P falciparum illustrated a rapid decline in burden between 2000 and 2017. However, 90.9% of the population in sub-Saharan Africa still remained at risk of contracting P falciparum in 2017.
The study results demonstrated that the increase in the global percentage of people living in P falciparum-free regions is likely a result of shifts from hypoendemicity to parasite-free. These regions were noted to be centered in south and southeast Asia, which demonstrated an increase from 1.8% to 17.9% and 71.8% to 82.2%, respectively, in the population of people living in P falciparum-free regions between 2005 and 2017. Researchers noted that the percentage of people in sub-Saharan Africa living in the highest burden areas has decreased significantly as well, from 24.5% in 2005 to 5.7% in 2017. In addition, the investigators reported that 7.3% of the Earth’s land surface (excluding Antarctica) transitioned from P falciparum-endemic to P falciparum-free between 2005 and 2017. This translates to 9.93 million km², or an area approximately the size of China
Overall, the study investigators concluded that, “By providing a means of establishing international and intranational heterogeneity, our maps serve as an essential tool for assessing progress and guiding future intervention planning from local to global scales.”
Weiss DJ, Lucas TC, Nguyen M, et al. Mapping the global prevalence, incidence, and mortality of Plasmodium falciparum, 2000-17: a spatial and temporal modelling study [published online June 19, 2019]. The Lancet. doi:10.1016/S0140-6736(19)31097-9