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The study of children in Africa estimates that 80 per cent of all new infections are concentrated in just one fifth of the population. Similar trends have been shown for a range of infectious disease systems. But the new research represents some of the most compelling evidence for this pattern in malaria, which kills around 2 million people every year, most of them children under-five.
A team including researchers from the National Institutes of Health's Fogarty International Centre in Washington and Princeton University in New Jersey, and Wellcome Trust funded scientists working at the University of Oxford and in Kenya published the study in the 24 November issue of Nature.
The team's paper shows the best way to ascertain the relationship between mosquitoes carrying the deadly malaria parasite, Plasmodium falciparum, and the rates of infection in African children is through a mathematical model incorporating heterogeneity.
These findings are based on field data from a number of studies of mosquito behaviour and records of infections in around 5000 children aged under 15 years living in more than 90 communities across Africa.
Dr David Smith, the lead author, based at the Fogarty International Centre, said "This paper shows that heterogeneity plays a very important role in transmission, a result that is important for planning and evaluating control measures. It also allows us to infer that the average malaria infection usually lasts about six months in a child and that children up to age 15 develop no resistance to new infections."
Co-author Dr Simon Hay, a Wellcome Trust Research Career Development Fellow based in Oxford's Department of Zoology and in Nairobi, said: "Why some children provide a more attractive target for mosquitoes carrying the malaria-causing parasite, Plasmodium falciparum, remains unclear, particularly in areas where transmission of the parasite between mosquitoes and man is so high.
"Identifying this small group of children in any particular locality will likely be very difficult. What is clear, however, is that interventions targeting prevention of bites from malaria-carrying mosquitoes should be delivered as widely as possible in a community to ensure those contributing most to the perpetual transmission of the parasite are protected from doing so. The current target of 60 per cent coverage, set by the African Heads of State in Abuja in 2000, might be too low."
Adapted from a news release by the University of Oxford.
Smith DL et al. The entomological inoculation rate and Plasmodium falciparum infection in African children. Nature 2005 Nov 24;438(7067):492-5. Abstract
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11/4/11 [WTD023969] Children are more attractive targets for mosquitoes.doc