Certain children are more attractive targets than others for malaria-carrying mosquitoes, accounting for most new infections of the disease that kills about 2 million people each year, scientists said on Wednesday.
They estimate that 80 percent of infections are concentrated in just one fifth of the population, who should be the focus of public health efforts to control the illness.
"Twenty percent of people receive 80 percent of all infections," Dr David Smith, of the National Institutes of Health in Bethesda, Maryland, said in a report in the journal Nature.
Smith and researchers from the United States, Kenya and Britain constructed a mathematical model to determine the proportion of people infected with the malaria parasite and the rate at which people are bitten by infectious mosquitoes.
Most malaria deaths occur in Africa where the disease kills a child every 30 seconds, according to the World Health Organization.
Using records of infection in about 5,000 children under the age of 15 in 90 communities in Africa and information from studies on mosquito behavior, the scientists discovered that some children play a more important role in the transmission of the disease.
"It is only a small proportion of the population that perpetuate transmission," said Professor Bob Snow, a malaria expert at the Kenya Medical Research Institute in Nairobi.
"It would be particularly hard to control malaria unless you targeted those superspreaders. But the trouble is we can't really identify them uniquely," he added in an interview.
The researchers do not know what makes a child more likely to be infected. It could involve genetic or immunological factors or they could be the poorest children in a community who do not sleep under bed nets so have no protection.
"Why some children provide a more attractive target for mosquitoes carrying the malaria-causing parasites, plasmodium falciparum, remains unclear," Dr Simon Hay, a member of the research team based in Oxford and Nairobi, said in a statement.
Interventions like mosquito nets should be targeted at them; otherwise the methods to control the disease will not work well.
"If we can't target them ... then the implication is that we have to make sure we cover everybody and we will definitely cover the 20 percent who are the largest contributor," said Snow.
The study also shows that infections last about 6 months on average and that a bout of malaria is not enough to confer immunity. Malaria occurs in more than 100 countries. About 40 percent of the world's population, including people living in the poorest countries, are at risk of malaria.
The Roll Back Malaria campaign, organized by the WHO, the United Nations Children's Fund, the United Nations Development Program and the World Bank, aims to halve malaria deaths by the year 2010.
