Fasciola gigantica: a new method for cercarial shedding from experimentally infected lymnaea cailliaudi snails. Observations on encystment of the metacercaria and accidental excitation

ABSTRACT

Lymnaea cailliaudi were collected from the field and proved to be uninfected. The snails were maintained in the laboratory and exposed experimentally to miracidia of Fasciola gigantica. Cercarial shedding was performed by three methods reported before, and another new method was developed in this study. The new method was done by apex puncture of the shell of infected snail. It has the advantage of collection of large numbers of mature cercariae in clean and small volume of fluid within few minutes. Cercariae were found mobile and unencysted for up to one week when maintained immediately after shedding at 4C. When the cercariae were taken out of the refrigerator, encystment was observed to occur rapidly before tail detachment. Accidental excystation of metacercariae was observed during microscopic examination of samples from the stored cysts in the refrigerator. This proved that heat and light are important factors initiating excystation of the parasite