Influence of the nontarget mollusc Marisa cornuarietis on the hourly cercarial production of Schistosoma mansoni from Biomphalaria glabrata.

A comparative study of hourly cercarial productivities of Schistosoma mansoni from infected Biomphalaria glabrata was carried out in the presence of either healthy B. glabrata (control) or healthy Marisa cornuarietis (experimental). The results showed that, with M. cornuarietis, almost all the hourly cercarial productivities increased by a factor varying from 1.3 to 2.5 without modification of the shedding period. Several species of nontarget molluscs (NTM) are responsible, under experimental conditions, for a significant stimulation of the daily cercarial productivity of Schistosoma mansoni from Biomphalaria glabrata (Mone et al., 1986). The enhanced cercarial productivity is nearly twice that of the control batch at the end of 1 of the experiments in the case of the NTM Marisa cor- nuarietis. Furthermore, the daily cercarial pro- duction of S. mansoni is known to display a circadian shedding rhythm almost exclusively restricted to the daylight hours (Theron, 1980). This shedding rhythm determines the daily pe- riods of high and low risks of contamination for ABSTRACT: A comparative study of hourly cercarial productivities of Schistosoma mansoni from infected Biomphalaria glabrata was carried out in the presence of either healthy B. glabrata (control) or healthy Marisa cornuarietis (experimental). The results showed that, with M. cornuarietis, almost all the hourly cercarial productivities increased by a factor varying from 1.3 to 2.5 without modification of the shedding period.