A comparison of re-infection rates with Schistosoma haematobium following chemotherapy in areas with high and low levels of infection

Two groups of children (6-15 years) from a Schistosoma haematobium endemic area were followed for 9 months after praziquantel treatment. Seventy-three children came from an area of high infection while 67 children came from a n area of low infection. Pre-treatment infection prevalence in the high inf ection area (76.6%) was significantly higher than that in low infection are a (36.3%). Levels of anti-SEA immunoglobulin (Ig)A and IgM were significant ly higher and levels of lgG3 significantly lower in children from the low i nfection area. Nine months after treatment, infection prevalence was signif icantly higher in the high infection area (29.0%) (where re-infection rates were higher) than in the low infection area (12.9%). Children from the hig h infection area were six times more likely to get re-infected than those f rom the low infection area, while younger children were 30 times more likel y to get re-infected than older children. These results are discussed in re lation to differences in transmission and the development of acquired immun ity. Pre-treatment levels of IgM and the difference between IgE and IgG4 we re positively associated with reinfection in the high infection area. These results are discussed in relation to the interpretation of simple correlat ions between infection and some antibody levels and the inference of causal relationships between observed epidemiological and immunological patterns.