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Rolling back malaria: A journey through space and time

By Philippa Matthews
Peter Medawar Building for Pathogen Research, Oxford, UK

This summary was awarded 1st place for Access to Understanding 2015

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Plasmodium falciparum is the most deadly of all malaria parasites. Children are particularly vulnerable to the devastating consequences of this infection: the World Health Organisation estimates that a child in Africa dies from malaria every minute1. In recognition of this crisis, malaria has become a headline priority for global health, with campaigns such as ‘Roll Back Malaria’ spearheading a huge international effort to tackle the disease.

Noor and colleagues set out to assess how much progress has been made across Africa in the ‘Roll Back Malaria’ era. Have the immense resources deployed made a real difference to some of the world’s most vulnerable populations? How has the burden of malaria altered in the decade since 2000? And can we identify whether infection risks have changed by country or region? With these questions in mind, this research team developed a sophisticated analytical method to measure, as precisely as possible, changing patterns of malaria risk in Africa.

The symptoms of malaria can mimic those of many other infections, and suspected cases of malaria are often treated without a certain diagnosis and without attending a hospital or clinic. For these reasons, trying to get a clear picture of the scale of the malaria problem in Africa is a major challenge. Noor’s team chose to measure malaria by the most accurate method available, by looking for studies that had actually identified Plasmodium falciparum parasites in the blood of study participants in the community. Their final analysis draws on data collected from 3.5 million individuals represented in over 26,000 surveys spanning 49 regions of Africa, with each piece of information linked to its precise geographic origin by satellite technology.

The researchers fed this vast mine of data into a carefully constructed computational analysis. Each piece of information was adjusted to account for exactly when and where it was collected, and to apply it to a particular age group of interest – the highly vulnerable population of children aged 2-10 years. They also factored in a host of complex influences on malaria transmission, such as urbanisation and climate. The final output was a measure of malaria risk for each individual square kilometre of Africa, first in 2000 and then again a decade later. Each of these tiny squares was classified into one of eight different malaria risk categories.

From this sophisticated analysis, Noor’s team report several substantial and encouraging improvements in the patterns of malaria in Africa. Strikingly, they calculated that 217 million people in Africa were living in a lower risk area in 2010 than they did in 2000, as well as finding an overall reduction in malaria transmission in 40 of the 44 African countries that they assessed in detail. Four territories, South Africa, Eritrea, Ethiopia and Cape Verde, successfully reduced malaria into the lowest risk category by 2010. By this time, the majority of the transmission in the highest risk category was occurring in just ten countries.

Noor’s study also sounds several important notes of caution. A population explosion in Africa has contributed hugely to the total numbers of people at risk of malaria; over 50% the continent’s total population still live in regions of substantial risk. Soberingly, this effect of population growth somewhat dilutes other gains that have been made in reducing malaria risk. Rates of infection in certain countries remained unchanged or even climbed between 2000 and 2010: Malawi and South Sudan are highlighted as areas for increasing concern, and high transmission has continued across many parts of Nigeria and the Democratic Republic of Congo.

The researchers also highlight some areas of difficulty. Despite a data collection effort that spanned eight years, they were still unable to identify enough information to assess the malaria risk for certain regions of Africa. And of course the vastly complex nature of malaria transmission cannot be completely captured or measured by a computer-based method.

Overall, however, the results of this meticulous analysis provide valuable feedback for improving population health in many parts of Africa. As well as amassing all possible information about malaria parasite distribution, the study team also thought hard about the impact of the rapidly changing social and geographical landscape of Africa, ranging from urbanisation to rainfall. Their detailed mapping of malaria patterns highlights how the risks of an infection can wax and wane, reminding us that the ‘Roll Back Malaria’ campaign and its allies need to be constantly re-assessing the best way to keep pace with changing patterns of disease. The authors conclude with cautious optimism about the progress made since 2000, but provide a timely warning that the challenge of malaria is far from over.

References

1http://www.who.int/mediacentre/factsheets/fs094/en/

This article describes the research published in:

The changing risk of Plasmodium falciparum malaria infection in Africa: 2000-10: a spatial and temporal analysis of transmission intensity
M. Noor, D. K. Kinyoki, C. W. Mundia, C. W. Kabaria, J. W. Mutua, V. A. Alegana, I. Socé Fall, R. W. Snow Lancet (2014) 383(9930), 1739–1747
http://EuropePMC.org/articles/PMC4030588

This article was selected for inclusion in the competition by the Wellcome Trust.

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