A Long Neglected World Malaria Map: Plasmodium vivax Endemicity in 2010

Abstract

Current understanding of the spatial epidemiology and geographical distribution of Plasmodium vivax is far less developed than that for P. falciparum, representing a barrier to rational strategies for control and elimination. Here we present the first systematic effort to map the global endemicity of this hitherto neglected parasite. We first updated to the year 2010 our earlier estimate of the geographical limits of P. vivax transmission. Within areas of stable transmission, an assembly of 9,970 geopositioned P. vivax parasite rate (PvPR) surveys collected from 1985 to 2010 were used with a spatiotemporal Bayesian model-based geostatistical approach to estimate endemicity age-standardised to the 1–99 year age range (PvPR_1–99) within every 5×5 km resolution grid square. The model incorporated data on Duffy negative phenotype frequency to suppress endemicity predictions, particularly in Africa. Endemicity was predicted within a relatively narrow range throughout the endemic world, with the point estimate rarely exceeding 7% PvPR_1–99. The Americas contributed 22% of the global area at risk of P. vivax transmission, but high endemic areas were generally sparsely populated and the region contributed only 6% of the 2.5 billion people at risk (PAR) globally. In Africa, Duffy negativity meant stable transmission was constrained to Madagascar and parts of the Horn, contributing 3.5% of global PAR. Central Asia was home to 82% of global PAR with important high endemic areas coinciding with dense populations particularly in India and Myanmar. South East Asia contained areas of the highest endemicity in Indonesia and Papua New Guinea and contributed 9% of global PAR. This detailed depiction of spatially varying endemicity is intended to contribute to a much-needed paradigm shift towards geographically stratified and evidence-based planning for P. vivax control and elimination. Plasmodium vivax is one of five parasites causing malaria in humans. Whilst it is found across a larger swathe of the globe and potentially affects a larger number of people than its more notorious cousin, Plasmodium falciparum, it receives a tiny fraction of the research attention and financing: around 3%. This neglect, coupled with the inherently more complex nature of vivax biology, means important knowledge gaps remain that limit our current ability to control the disease effectively. This patchy knowledge is becoming recognised as a cause for concern, in particular as the global community embraces the challenge of malaria elimination which, by definition, includes P. vivax and the other less common Plasmodium species as well as P. falciparum. Particularly conspicuous is the absence of an evidence-based map describing the intensity of P. vivax endemicity in different parts of the world. Such maps have proved important for other infectious diseases in supporting international policy formulation and regional disease control planning, implementation, and monitoring. In this study we present the first systematic effort to map the global endemicity of P. vivax. We assembled nearly 10,000 surveys worldwide in which communities had been tested for the prevalence of P. vivax infections. Using a spatial statistical model and additional data on environmental characteristics and Duffy negativity, a blood disorder that protects against P. vivax, we estimated the level of infection prevalence in every 5×5 km grid square across areas at risk. The resulting maps provide new insight into the geographical patterns of the disease, highlighting areas of the highest endemicity in South East Asia and small pockets of Amazonia, with very low endemic setting predominating in Africa. This new level of detailed mapping can contribute to a wider shift in our understanding of the spatial epidemiology of this important parasite.