Cross-sectional study of specific antibodies to a polymorphic Plasmodium falciparum antigen and of parasite antigen genotypes in school children on the slope of Mount Cameroon.

To investigate relationships between Plasmodium falciparum parasitaemia, parasite genotypes, and specific anti-parasite antibodies, 244 school children (aged 4 to 16 years) were studied in April/May 2002, the peak malaria transmission season in Buea, Cameroon. Antibody reactivities were analysed by ELISA using an array of recombinant antigens representing different sequences from the polymorphic block 2 region of the merozoite surface protein 1 (MSP1), and the blood samples that were slide-positive for P. falciparum were genotyped for msp1 block 2 alleles. The prevalence of antibodies to the specific MSP1 block 2 antigens was significantly higher in children at one particular school (situated at the lowest altitude) compared to the others, although the prevalence of infection or particular parasite genotypes did not differ. Thus, at a population level, the prevalence of these antibodies does not simply reflect prevalence of parasites, but rather may be due to differences in the incidence of past infections. However, there were weak positive associations between specific antibody reactivity and the presence of the corresponding allele in the blood of individuals (statistically significant for the MAD20-type allele of block 2), indicating that antibody specificities are to some extent determined by current parasite infections.