Abstract

The rate and densities of Plasmodium falciparum reinfections were investigated in children five to 14 years old from one village in Tanzania with a high transmission rate. Initial parasitemias were eradicated by a curative treatment with quinine, a drug with a short elimination half-life, to minimize the effects of residual drug on reinfection. The seroreactivities to seven oligopeptides, representing T and B cell epitopes from the ring erythrocyte surface antigen (Pf155/RESA), the clustered arginine-rich protein antigen (CARP), and the circumsporozoite (CS) proteins were determined in the children at the start of the study and after 28 days. All children were reinfected within 42 days (mean 27 days). The geometric mean maximum parasite density at reinfection was 308 parasites per microliter (range 4-13, 920). The antipeptide antibody levels showed high interindividual variation, with a significant mean decrease (16%) between days 0 and 28 for the blood stage antigens, but not for the (NANP)6 peptide from the CS protein. This suggests that the absence of blood stage antigenic stimulation had already influenced the antibody levels within this short period of time. The mean reinfection day was not influenced by the levels of antibodies to any of the peptides. However, the children with higher antibody levels to (EENVEHDA)2(EENV)2 developed significantly lower parasitemias than those with lower antibody levels (P less than 0.05). This suggests that this subunit of the Pf155/RESA molecule is an important B cell epitope for protective antiparasitic immunity.