An In Vitro Study of the Relative Importance of Bile and Carbon Dioxide in the Activation of Fasciola Gigantica Metacercariae

Abstract

The relative importance of bile and atmospheric stimuli in activating metacercariae of Fasciola gigantica prior to excystment has been studied by omitting each in turn from the in vitro excystment medium, and by separating each from the period of incubation at 37°C. The results indicate that bile is less important than carbon dioxide in triggering excystment, and may serve only to increase the permeability of the cyst wall to carbon dioxide. It is speculated that activation involves initiation of carbon dioxide fixation and anaerobic metabolism due to the high concentration of carbon dioxide and low redox potential prevalent in the gut.