Mapping the global endemicity and clinical burden of Plasmodium vivax, 2000-17: a spatial and temporal modelling study

Abstract

Background: Plasmodium vivax exacts a significant toll on health worldwide, yet few efforts to date have quantified the extent and temporal trends of its global distribution. Given the challenges associated with the proper diagnosis and treatment of P vivax, national malaria programmes-particularly those pursuing malaria elimination strategies-require up to date assessments of P vivax endemicity and disease impact. This study presents the first global maps of P vivax clinical burden from 2000 to 2017.

Methods: In this spatial and temporal modelling study, we adjusted routine malariometric surveillance data for known biases and used socioeconomic indicators to generate time series of the clinical burden of P vivax. These data informed Bayesian geospatial models, which produced fine-scale predictions of P vivax clinical incidence and infection prevalence over time. Within sub-Saharan Africa, where routine surveillance for P vivax is not standard practice, we combined predicted surfaces of Plasmodium falciparum with country-specific ratios of P vivax to P falciparum. These results were combined with surveillance-based outputs outside of Africa to generate global maps.

Findings: We present the first high-resolution maps of P vivax burden. These results are combined with those for P falciparum (published separately) to form the malaria estimates for the Global Burden of Disease 2017 study. The burden of P vivax malaria decreased by 41·6%, from 24·5 million cases (95% uncertainty interval 22·5-27·0) in 2000 to 14·3 million cases (13·7-15·0) in 2017. The Americas had a reduction of 56·8% (47·6-67·0) in total cases since 2000, while South-East Asia recorded declines of 50·5% (50·3-50·6) and the Western Pacific regions recorded declines of 51·3% (48·0-55·4). Europe achieved zero P vivax cases during the study period. Nonetheless, rates of decline have stalled in the past five years for many countries, with particular increases noted in regions affected by political and economic instability.

Interpretation: Our study highlights important spatial and temporal patterns in the clinical burden and prevalence of P vivax. Amid substantial progress worldwide, plateauing gains and areas of increased burden signal the potential for challenges that are greater than expected on the road to malaria elimination. These results support global monitoring systems and can inform the optimisation of diagnosis and treatment where P vivax has most impact.

Funding: Bill & Melinda Gates Foundation and the Wellcome Trust.

Figure 1

Temporal trends in Plasmodium vivax incidence and case counts from 2000 to 2017 The lines represent the temporal trends of incidence (A) and clinical case counts (B) of each WHO region. The shaded areas represent the 95% uncertainty intervals of these estimates. EMRO=Eastern Mediterranean Regional Office. PAHO=Pan American Health Organization. WPRO=Regional Office for the Western Pacific. AFRO=Regional Office for Africa. EURO=Regional Office for Europe. SEARO=Regional Office for South-East Asia.

Figure 2

Predicted incidence of Plasmodium vivax malaria in 2005 and 2017 Incidence in cases per 1000 people per year are shown on a spectrum of white (zero incidence) to dark grey (1 case per 1000) and then blue to red (>1 case per 1000 to >600 cases per 1000) for the years 2005 (top panel) and 2017 (bottom).

Figure 3

Relative uncertainty of Plasmodium vivax incidence pixel-level allocation The relative uncertainty values for 2005 (top) and 2017 (bottom), as calculated by the SD divided by the square root of the mean are shown on a spectrum of blue (most certain) to yellow (least certain). These uncertainty values relate to distribution of cases rather than the certainty of the case counts themselves.

Figure 4

Predicted Plasmodium vivax clinical cases and change from 2005 and 2017 The numbers of cases predicted to occur in each 5 × 5 km pixel are shown on a spectrum of blue to red for the years 2005 (top panel) and 2017 (middle). Areas where P vivax is known to be endemic, but there was not sufficient information to generate a prediction are shown in light grey. The bottom panel shows change calculated by the value for 2005 minus 2017 divided by the 2005 value and multiplied by 100, such that a decrease is shown on a scale of white to green and an increase from white to pink. The darkest green areas have seen a 100% or greater decrease in P vivax cases from 2005 to 2017, while the darkest pink areas show a 100% or greater increase in cases.

Figure 5

Predicted Plasmodium vivax parasite rate and change 2005 and 2017 The prevalence in ages 1 to 99 years predicted to occur in each 5 × 5 km pixel are shown on a spectrum of light blue to red for the years 2005 (top panel) and 2017 (middle). Areas where P vivax is known to be endemic, but there was not sufficient information to generate a prediction are shown in light grey. The bottom panel shows change calculated by the value for 2005 minus 2017 divided by the 2005 value and multiplied by 100, such that a decrease is shown on a scale of white to green and an increase from white to red. The darkest green areas have seen a ≥100% decrease in prevalence from 2005 to 2017, while the darkest red areas show a ≥100% increase in prevalence.