IN-VIVO AND ECTOPIC ENCYSTMENT OF ECHINOSTOMA-REVOLUTUM AND CHEMICAL EXCYSTATION OF THE METACERCARIAE

In vivo and ectopic encystment of the cercariae of Echinostoma revolut um from Lymnaea elodes snails in Indiana and chemical excystation of t he metacercariae were studied. In vivo encystment occurred in adults o f Biomphalaria glabrata and Helisoma trivolvis (Colorado strain) snail s and in neonatal and juvenile L. elodes snails. These results were ex pected because 37-collar-spined Echinostoma species show broad specifi city in their second intermediate gastropod hosts. Encysted metacercar iae of E. revolutum and Echinostoma trivolvis removed from experimenta lly infected snails and treated in a trypsin-bile salts excystation me dium at 39 C showed 30.3% excystation for the former and 55.7% for the latter at 4 hr. The ducts and openings of the paraesophageal glands o f excysted metacercariae of E. revolutum from cysts formed in snails d id not stain with neutral red. Abnormal ectopic cysts with distorted o uter walls and granular inner walls were obtained within 48 hr of plac ing E. revolutum cercariae in Locke's 1:1 plus 1% dextrose. These meta cercariae excysted rapidly in the excystation medium and their paraeso phageal,oland ducts and openings stained with neutral red. Differences in ectopic encystment and chemical excystation in vitro can be used t o distinguish these closely related species in the E. revolutum comple x.