Mapping malaria – a new analysis of spatial limits and transmission intensity

The KEMRI-Oxford group has published a new map of malaria transmission. This is a terrific accomplishment providing a global picture of falciparum malaria and answers some basic questions: where is malaria a risk and how intense is that risk? Using results from 4,278 surveys, the researchers found approximately 2.37 billion people live in areas at risk of malaria infection of which 1 billion live in areas of unstable or low transmission. Furthermore, areas of high parasite rates (>50%) are largely in sub-Saharan Africa while other malaria endemic areas are largely hypoendemic (<10%).

While mapping transmission is easier than estimating the number of worldwide cases, it is an undertaking fraught with significant obstacles. In the accompanying editor’s summary, Stephen Rogerson duly notes the accuracy of the findings are dependent on the author’s assumptions and the accuracy of the underlying data. Quite honestly, some of the methodology used in the paper is a bit beyond my skills, but most of the assumptions presented seemed very reasonable and the authors are terrific researchers. I think the spatial limits are more likely to be accurate than transmission intensities due to challenges with the input data. Cross sectional surveys are subject to multiple biases including death bias, seasonal bias, and missing asymptomatic infections. Furthermore, as the authors note, the data is not population representative which is a deficiency plaguing the surveillance of most tropical diseases and a crucial challenge to address for effective control.

Regardless of the precise numbers, the larger trends described can support a logical conclusion, one which many people have previously advocated. We can eliminate malaria outside of sub-Saharan Africa as these regions are of low and unstable transmission and yet comprise almost half of the world’s population at risk for malaria. It’s an exciting proposition and a growing possibility.

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