Viability of the Encysted Metacercariae of Echinostoma caproni Judged by Light Microscopy Versus Chemical Excystation

The purpose of this study was to determine the viability of encysted metacercariae of Echinostoma caproni stored in Locke's solution 1:1 at 4 C for 1–24 wk. Viability was judged by light microscopy (LM) based on morphological characteristics of the encysted metacercariae versus chemical excystation of the cysts in a trypsin–bile salts excystation medium. The percent viability was very similar under both methods of assessment at 4, 8, and 16 wk poststorage. At 1 and 24 wk poststorage, viability was found to be about 2× greater based on excystation than using LM. We concluded that LM alone underestimated the viability of cysts and that determination of cyst viability was more accurate under assessment by chemical excystation.