November 23, 2005

Malaria affects some children more than others

By Patricia Reaney

LONDON (Reuters) - 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

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 (WHO).

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

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 (UNICEF), the United Nations
Development Program (UNDP) and the World Bank, aims to halve
malaria deaths by the year 2010.