In vitro pairing of Echinostoma revolutum (trematoda) metacercariae and adults, and characterization of worm products involved in chemoattraction.

In vitro pairing studies were done on chemically excysted metacercariae and on adults of Echinostoma revolutum maintained in vitro in agar-Locke's petri dish cultures at 39 +/- 1 C for up to 24 hr. Whereas newly excysted metacercariae did not pair, both immature and mature adults showed significant pairing. Adult echinostomes confined in dialysis sacs emitted excretory-secretory (EC) 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 three 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 analyses of free sterols of E. revolutum have indicated that cholesterol is the major free sterol.