Dynamics of larval populations ofSchistosoma mansoniinBiomphalaria glabrata

Abstract

The production of cercariae of Schistosoma mansoni by Biomphalaria glabrata infected with a single miracidium is characterized by very irregular daily emissions and by the alternation of periods of high and low emissions, which give rise to a circamensual production rhythm. The cercarial production index of the Brazilian host-parasite combination is 160 cercariae per day and per snail (c/d/s) under conditions of constant temperature of 26°C; balanced photoperiod (12 hours: 12 hours) and a luminous intensity of 1200 ergs/cm²/second. A decrease in temperature from 26°C to 24°C during the prepatent period induces a drop of 33% of the cercarial production index. The rhythmic fluctuations in production are in relation to the demography of the intra-molluscan larval stages. Periods of high cercarial production would correspond to successive generations of cercariae.