Malaria and urbanization in central Africa: the example of Brazzaville. Part IV. Parasitological and serological surveys in urban and surrounding rural areas.

Five schools were chosen in different districts of Brazzaville where the intensity of malaria transmission, determined in a previous study, is representative of the very varied conditions observed in this town in relation to urbanization. The parasitological and serological results found in schoolchildren are analysed according to the level of transmission to which they are exposed, and compared with the results of a longitudinal survey carried out in the rural area of the Brazzaville region. In the urban area malaria prevalences in schoolchildren aged from 5 to 9 years and from 10 to 14 years vary considerably according to the districts. They are, respectively, 78.9% and 84% in Massina, 58.8% and 71.7% in Talangai, 32.3% and 46.9% in Bacongo and 5.6% and 12.6% in Moungali. In Poto-Poto, no positive thick films were found in a representative sample of 62 schoolchildren aged 6 and 7 years who have always lived in this district, and the malaria prevalence is only 6.9% in schoolchildren aged 14 and 15. In the rural area, the malaria prevalence is 76.4% in schoolchildren aged 5 to 9 and 82% in those aged from 10 to 14. According to standard immunofluorescent technique, 63% of children aged 6 and 7 years living since birth in the central part of the Poto-Poto and Moungali districts have no detectable antibodies. In the rural area, all children over 4 years of age are seropositive. These results show that the decrease in vectorial density which accompanies urbanization has considerable parasitological repercussions.(ABSTRACT TRUNCATED AT 250 WORDS)