Survival and infectivity of Hypoderaeum conoideum and Euparyphium albuferensis cercariae under laboratory conditions

The survival characteristics of the cercariae of Hypoderaeum conoideum and Euparyphium albuferensis (Trematoda: Echinostomatidae) at 20 degrees C and 30 degrees C are described, and the age dependency of their infectivity at 20 degrees C is studied to determine their respective transmission efficien cies. Cercarial survival was found to be age-dependent and was higher at 20 degrees C. For both cercariae, the maximum life-span was 26 h at 20 degree s C and 16 h at 30 degrees C, and their respective times to 50% mortality w ere similar at each temperature. Both cercariae seem to be well adapted to transmission in their natural habitat, though cercarial infectivity of H. c onoideum was higher than that of E. albuferensis, this being correlated wit h their prevalences in nature. The age-dependency of cercarial survival may be related to steadily diminishing endogenous energy levels, though the de lay in attaining maximum infectivity suggests that other factors not relate d to energy considerations are involved in the delimitation of the cercaria l infective period. However, this latter observation may constitute an adap tative mechanism allowing cercarial dissemination.