Schistosoma haematobium: comparative studies on prevalence and cercarial shedding according to the shell diameter of Planorbarius metidjensis at miracidial exposure.

Experimental infections of Planorbarius metidjensis by Schistosoma haematobium were carried out under controlled conditions to determine whether there was a size limit after which the snail could not longer sustain Schistosoma infection. Snails measuring 1-6 mm in diameter were exposed to two miracidia each and were raised at 24-26 degrees C until their death. The frequency of snails with cercarial shedding was 63% in the 2.1- to 3-mm group. In the other groups the frequencies were lower, decreasing to 2.8% in the 5.1- to 6-mm group. The periodicity of S. haematobium cercarial shedding was not modified by the snail diameter at miracidial exposure.