Ecological studies in Madagascar of Biomphalaria pfeifferi, intermediate host of Schistosoma mansoni. 2. Biology and dynamics in the non-endemic area of Antananarivo.

The region of Antananarivo, where Schistosomiasis is not yet endemic, is compared to Ambositra, a well established focus of S. mansoni, with regard to climate, hydrology and snail habitats. Higher mean temperatures and a more pronounced dry season in Antananarivo contribute to sometimes less favourable hydrological conditions. Biomphalaria is found in very few and limited habitats. Population dynamics were followed up in selected habitats and showed ecological parameters comparable to those of the Ambositra-strain. Trematode infections were very scarce. Both strains of Biomphalaria are equally susceptible to infections with the malagasy strain of S. mansoni (up to 100 p. 100). Mortality rates, prepatency periods and the electrophoretic pattern of egg proteins are very similar. Foreign snail species like B. glabrata (albino strain) and B. pfeifferi (South African strain) are hardly susceptible to malagasy S. mansoni. Some cases of S. mansoni-infections are mentioned, which presumably had been contracted in non-endemic areas of the province of Antananarivo. The possibility and risk of implantation of schistosomiasis in this region and in the town is evaluated following the discussion of epidemiological details. The author concludes that in spite of some unfavourable conditions for S. mansoni the establishment of the cycle can locally not be excluded. Attention is all the more important, as control of endemic schistosomiasis would be particularly difficult under malagasy conditions of geography, climate, snail dynamics and human behaviour.