The malaria parasite tends to cause more severe disease in young children. This could be because the parasite expresses genes associated with the severe form of malaria in people with limited immune defences, according to Peter Bull of the Kenya Medical Research Institute in Kilifi and his colleagues.
The researchers sequenced portions of key virulence genes — the var genes — from malaria parasites obtained from 217 Kenyan children, 112 of whom had severe disease. Certain var genes were expressed at higher levels in younger children and in those with more severe forms of the disease. The researchers also found that higher var gene expression correlated with low levels of antibodies for parasite-infected cells. The team suggests that the parasite can take advantage of low host immunity to cause more severe malaria.