A longitudinal investigation of Plasmodium falciparum malaria in children in northern India.

A group comprising 27 young children (1-4 y of age) suffering from uncomplicated falciparum malaria were studied to characterize the isolates and to measure humoral immune responses during acute infection and after recovery. Finger prick blood from each individual was collected on d 1. After treatment with chloroquine, a further blood sample was collected from each child on d 7, 30, 90 and 180 for assay of antibody responses to P. falciparum antigens. Isolates from individual patients were incubated in vitro for demonstration of rosette formation, assay of plasmodial growth rate and analysis of Pfcrt gene polymorphism. Out of 27 isolates of P. falciparum, 20 showed formation of rosettes in vitro. The growth rate at 96 h varied widely among the isolates. In Pfcrt gene analysis at 76-codon site, 14 showed wild-type Lys 76, 7 showed mutant type Thr 76 and 6 had mixed type. 14 children, all with anaemia on d 7, showed a positive direct antiglobulin test (DAT). Sera positive by ELISA IgG on d 90 also showed parasite growth inhibitory activity in vitro. Significant levels of IgG, IgG1 and IgG3 subclass antibodies against MSP1 were detected in 14 sera collected on d 90. On d 180, there was a decline in IgG and its subtypes. These findings suggest that a variability in isolates may occur in one and the same seasonal area, making children prone to infection. As a consequence, they develop antibodies during recovery phase from an acute attack, which remain in circulation for a period of 4-5 months. After that, a decline in antibody level may again make them susceptible to the disease. Prevalence of different serotypes in a small area may suggest the complexity of malaria transmission.