Review
The global distribution and population at risk of malaria: past, present, and future

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Summary

The aim of this review was to use geographic information systems in combination with historical maps to quantify the anthropogenic impact on the distribution of malaria in the 20th century. The nature of the cartographic record enabled global and regional patterns in the spatial limits of malaria to be investigated at six intervals between 1900 and 2002. Contemporaneous population surfaces also allowed changes in the numbers of people living in areas of malaria risk to be quantified. These data showed that during the past century, despite human activities reducing by half the land area supporting malaria, demographic changes resulted in a 2 billion increase in the total population exposed to malaria risk. Furthermore, stratifying the present day malaria extent by endemicity class and examining regional differences highlighted that nearly 1 billion people are exposed to hypoendemic and mesoendemic malaria in southeast Asia. We further concluded that some distortion in estimates of the regional distribution of malaria burden could have resulted from different methods used to calculate burden in Africa. Crude estimates of the national prevalence of Plasmodium falciparum infection based on endemicity maps corroborate these assertions. Finally, population projections for 2010 were used to investigate the potential effect of future demographic changes. These indicated that although population growth will not substantially change the regional distribution of people at malaria risk, around 400 million births will occur within the boundary of current distribution of malaria by 2010: the date by which the Roll Back Malaria initiative is challenged to halve the world's malaria burden.

Section snippets

Spatial distribution of malaria through time

The human race and malaria parasites have had a long evolutionary host-parasite association.2, 3, 4 Advances in bioinformatics5, 6 largely support hypotheses inferred from changes in human ecology that around 10·000 years ago Plasmodium falciparum populations rapidly expanded in Africa and spread worldwide, coincident with human population growth and subsequent diasporas facilitated by the dawn of agriculture.7, 8 It has also been suggested that this expansion followed an earlier smaller wave

Human populations at risk through time

The global human population has grown geometrically during the 20th century from approximately 1 to 6 billion (table 1). These demographics have important implications for the percentage of the human population exposed to all-cause malaria risk through time. The percentage of the global population at risk has decreased from 77% at the turn of the 20th century to a low of 46% in 1994. This figure increased to 48% in 2002 due to population growth in an unchanged geographic distribution. In

Global malaria control from ~1900 to 2002

During the 19th century great improvements in the control of several communicable diseases were realised, chiefly as a result of environmental improvements.48, 49, 50, 51, 52 In parallel, improved social conditions (particularly housing) and changing land use (particularly agricultural practices) contributed significantly to the global reduction in the distribution of malaria.8, 21, 53, 54, 55, 56 These gains from malaria control were often coincidental with economic and social development,

Malaria burden

There has been a renewed interest in establishing precise estimates of morbidity and mortality as part of the Global Burden of Disease Programme.96, 97 Almost all of this work, including studies on acute respiratory-tract infections,98 HIV/AIDS,99 and malaria,30, 31 has been driven by the use of empirical survey data, modelled and extrapolated to wider areas. These studies are all critically dependent on the denominator population at risk. For a vector-borne disease such as malaria, the

Conclusions

No recent global maps of malaria endemicity have been developed since those of Lysenko in 1968,9 despite significant advances in the collection of empirical data, global environmental information from satellites, and the statistical techniques that can be used to integrate them.28, 29 In addition, given the poor health information systems in the AFRO area it is paradoxical that some of the best information on malaria endemicity and burden exists for this region.27, 28, 29 We suggest therefore

Search strategy and selection criteria

Data for this review were identified through PubMed Medline, the Bodleian library at Oxford, manual searches of the WHO's Weekly Epidemiological Record (http://www.who.int/wer/en/), suggestions of reviewers (formal and informal), and the bibliographies of the resulting articles. We used the following Boolean search statement: “malaria” and (“distribution” and “maps”), “malaria” and (“burden” or “risk”), “malaria” and (“control” and “campaign”). Articles in all languages were selected and

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