[Prevalence of Schistosoma haematobium schistosomiasis in Mayo Danaï (North Cameroon)]. / Prévalence de la schistosomiase à Schistosoma haematobium dans le Mayo Danaï (Nord Cameroun).

The state of the S. haematobium infection in North Cameroon seemed sufficiently well known to regard as negligible the risks involved in planning hydro-agricultural plants. However, a series of field-studies conducted by the authors in one of these sites (SEMRY II, North of Yagoua, in the Mayo Danaï area) has shown that the spread of this disease varies widely from village to village. It is sometimes absent, and on average, it rarely exceeds 15% of the sample (approximately 4,000 people, spread over 28 survey areas). This result is obtained using a representative sample of about 70,000 people, directly or indirectly affected by the hydro-agricultural project. The technique used was a simple centrifugation, and no egg count was made. Two malacological investigations performed in the same area complemented the parasitological inquiry. Comparison of these results with previous works shows that the latter used too few observations, the statistical representativity of which was never assured. On the other hand, recent evaluations, done independently of those reported in this paper, but which are limited to a few villages, confirm that the present infection rate for S. haematobium is appreciably lower than what is believed, and that it varies considerably from village to village. This re-evaluation of the problem leads us to conclude that the hydroagricultural plants, which are intended to develop irrigated rice-growing, might cause a considerable upsurge of the disease; and that this risk should be prevented by setting up specific control programs.

[Epidemiologic study of S. haematobium bilharziasis in the rice fields of Yagoua (North Cameroon) II. Distribution and ecology of intermediate hosts]. / Etude épidémiologique de la bilharziose à S. haematobium dans le périmètre rizicole de Yagoua (Nord-Cameroun) II. Distribution et écologie des hôtes intermédiaires.

While inventoring the local malacological fauna and evaluating the density of species acting as intermediate hosts of human schistosomes it has been shown that Bulinus truncatus is predominant in the study area. Bulinus globosus is scarcely encountered. Biomphalaria pfeifferi is only found in the Mayo Guerleo, in irrigation canals and draining ditches. But B. globosus and B. pfeifferi have not yet invaded the recent aquatic network and are not found in the lake nor in the newly created irrigation systems. Snails shedding cercariae of S. haematobium and S. mansoni have been collected in the area. Bulinus forskalii is found in all types of permanent of temporary waterbodies but S. intercalatum has not yet been reported from North-Cameroon. Lymnaea natalensis, the intermediate host of Fasciola gigantica, is found in the lake and in the canals, in the Mayo Guerleo and in the Toupasko pool. The rice field does not form by itself a favorable environment for snails to develop in it. Spots where transmission occurare more often in the area the secondary of tertiary irrigation canals and the brains. The ditches obstructed by plants are the places where the snails are developing best. Bulinus spp. are found in large numbers in the lowest parts of the aquatic network and they accumulate there to survive drought conditions in the mud. The recently built irrigation systems are not massively invaded by the snails yet and the prevalence of bilharziasis in the area correspond to the distribution of the intermediate hosts of schistosomes and to the density of the snails populations.