Measuring children’s immunity to malaria in Kenya

Children in the villages around Kilifi on the coast of Kenya are vulnerable to malaria, a disease that still kills a child in Africa every few minutes. However, among their community the KEMRI-Wellcome Trust Research Programme, headed by Professor Kevin Marsh, is endeavouring to understand, treat, and wherever possible prevent the disease.

The programme is a partnership between the Kenya Medical Research Institute, Oxford University, and the programme's major funder the Wellcome Trust. The labs at Kilifi are a hub for a wide network of field researchers whose starting point is close surveillance of the health of 250,000 adults and children living nearby. Surveillance involves regular visits to homes, occasional blood sampling, and monitoring of those who arrive for treatment at the Kilifi General Hospital.

'Malaria is a major problem for children in Africa,' says Professor Marsh. He points out that there has been a change in recent years in the focus of research, partly because measures such as the use of insecticide-treated bednets have begun to control the spread of infection. 'The kinds of vaccines we'll need in the future have changed, because of the way that malaria control is reducing malaria', he says.

Professor Marsh's colleague Dr Faith Osier is studying the role of antibodies in immunity to malaria, knowledge that will be crucial in understanding the effectiveness of new vaccines. 'People living in malaria-endemic areas become immune to death from severe malaria by the age of five years', she says. 'But we don't understand the mechanism of this acquired immunity very well.'

Dr Osier has developed a method of measuring the relative quantities of different antibodies to the malaria parasite in the blood of children up to the age of 10 years. She is then able to assess their effectiveness in protecting the children from bouts of clinical malaria. She has established that antibodies provide a substantial level of protection, but only if they are present above certain threshold concentrations.

She also found that children from different villages in the Kilifi study area vary in the strength of their antibody responses. Children were most likely to have antibody levels above the protective threshold if they lived in areas where the frequency of mosquito bites was relatively high. These children often have parasites in their bloodstream, yet do not fall ill. It looks as though high exposure to the parasite makes you better able to fight it in future – if it does not kill you in infancy.

'Faith's work has given us an important tool in measuring both naturally-acquired immunity, and immunity induced by trial vaccine programmes', says Professor Marsh.