ArticlesRelation between severe malaria morbidity in children and level of Plasmodium falciparum transmission in Africa
Introduction
Plasmodium falciparum is probably the single most important pathogen encountered by children growing up in sub-Saharan Africa. About 1 million African children die of malaria every year and millions more suffer both the mild and severe clinical consequences of infection. Everyone living in an endemic area becomes infected with P falciparum during childhood yet only a small proportion experience life-threatening complications.1, 2
Despite our increasing knowledge of the genetic and molecular basis of this parasite we do not know what determines the outcome of individual infections or how outcome varies with exposure at a population level. A clearer understanding of the relation between the frequency of exposure and the development of immune mechanisms which prevent death is essential to rationalise malaria interventions aimed at reducing host-parasite encounters.3 We document, for the first time, the epidemiological features of severe, potentially life-threatening malaria morbidity across a range of malaria ecologies typical of sub-Saharan Africa.
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Study populations
Five communities in Kenya and The Gambia were selected on the basis of their proximity to hospitals with clinical research teams providing detailed surveillance of all paediatric admissions. The geographical limits of these communities were predefined using local administrative boundaries and represented by either surveyed populations or discrete villages with stable populations. The five were: the area immediately surrounding Siaya District Hospital in western Kenya, communities north and
Transmission intensity
The five childhood communities differed greatly in their-risks of P falciparum infection (table 1). At Bakau the prevalence of infection among children aged 1–9 years was 2%,4 less than one-tenth that for Sukuta village only 8 km away. Similarly, dramatic differences were observed between the two communities separated by only a few kilometres north and south of Kilifi District Hospital. The highest rates of infection were observed in children in Siaya. The estimated force of infection (h)
Discussion
There is much debate over the long-term effects of control measures which reduce malaria transmission (eg, insecticide-treated bednets or transmission-blocking vaccines) upon the development of immunity to malaria.3, 17 Similar discussions were held over 50 years ago18, 19, 20 but until now the debate has been hampered by a lack of reliable data on relations between intensity of parasite transmission and disease outcome. The most important consequence of malaria infection is death. However, the
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