Epidemiology of Plasmodium falciparum in a rice field and a savanna area in Burkina Faso. Comparative study on the acquired immunoprotection in native populations.

A longitudinal study, including entomological, parasitological, immunological and clinical data, was carried out in a rice field and a savanna village in Burkina Faso. In this study, the authors followed the evolution of several parasitological parameters in order to compare the level of immunoprotection in children of these two areas. In particular, the percentages of recently 'infected' or 'recovered' children were calculated, during the interval separating two consecutive surveys. In both areas, parasite densities quickly increased in children from 0 to 14 years old, immediately after the beginning of the transmission period. In savanna, during the rainy season (May-October), parasite densities decreased and the proportion of recently 'recovered' children from 0 to 4 years old (becoming parasitologically negative between two consecutive surveys) was very low. On the other hand, parasite densities decreased and the recovery rate was higher in children from 10 to 14 years old before the end of the rainy season, while the transmission was going on. In the rice field area, Plasmodium falciparum densities decreased only at the end of the transmission period (December) and had the same levels as those found in savanna, in spite of a lower inoculation rate. The second peak of transmission seemed neither to increase the proportion of recovered children, nor to boost the immunoprotection of these children.