SCHISTOSOMA-MANSONI - EFFECT OF ESTIVATION ON THE INTRA-MOLLUSCAN STAGES AND THE SURVIVAL RATE OF INFECTED BIOMPHALARIA-PFEIFFERI

Following exposure to the miracidia of Schistosoma mansoni, Biomphalar ia Pfeifferi were induced to aestivate immediately ('0 h') or on days 7, 14 or 21 post-infection and then re-activated at various times. The proportions of snails found to be alive at weekly intervals after re- activation were found to be related to the length of time the snails h ad spent between infection and aestivation (I-A), varying from 100% (0 h) to 5% (21 days). The mean numbers of cercariae produced by the sna ils after re-activation also varied with I-A, being highest in those t hat aestivated immediately post-infection, and cercarial development w as delayed by prolonged desiccation of the infected snails, the intra- molluscan development of S. mansoni is affected by the aestivation of the snail host.