In vitro Pairing of Echinostoma revolutum (Trematoda) Metacercariae and Adults, and Characterization of Worm Products Involved in Chemoattraction

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Abstract
In vitro pairing studies were done on chemically excysted metacercariae and on adults of E. revolutum maintained in vitro in agar-Locke''s petri dish cultures at 39 .+-. 1.degree. C for up to 24 h. Newly excysted metacercariae did not pair; immature and mature adults showed significant pairing. Adult echinostomes confined in dialysis sacs emitted excretory-secretory (ES) products which significantly attracted single echinostome adults in vitro. Only the lipophilic fraction of ES products was found to elicit attraction. Preparative TLC analysis of adult echinostomes produced 3 major bands, as follows: I (phospholipids); II (free sterols); and III (free fatty acids + triglycerides). When tested in vitro, only the free sterol fraction significantly attracted single adult echinostomes. TLC and GLC [gas layer chromatography] analyses of free sterols of E. revolutum indicated that cholesterol is the major free sterol.