Various physical and chemical factors were studied to determine their effects on the viability of encysted metacercariae of Echinostoma caproni. Viability was equated with chemical excystation in an alkaline
trypsin-
bile salts (TB) medium. Control
cysts showed excystation percentages of > 90% in TB. Excystation proved to be a more reliable criterion of
cyst viability than observations by light microscopy. Isolated
cysts and
cysts left in the snail (in situ
cysts) were studied. Generally, in situ
cysts proved more resistant to various physical and chemical treatments than did isolated
cysts.
Cysts stored for 7 days at 28 C in a Locke's 1:1
solution showed 97% excystation, suggesting that
cysts of this species would survive postal delays during shipment. Of numerous marinades tested, the one that was most harmful to isolated and in situ
cysts was
vinegar. Isolated and in situ
cysts were killed by boiling (100 C) for 1 or 3 min, but freezing
at -10 C did not kill all isolated or in situ
cysts after 24 hr. Concentrations of
potassium permanganate ranging from 300 to 1,200 mg/L killed most isolated
cysts within 5 min, but in situ
cysts survived these concentrations for 24 hr. Concentrated solutions of NaCl and
sucrose had no effect on the viability of isolated and in situ
cysts, suggesting that their use in food preparations for molluscs would not be effective in killing echinostomatid
cysts in tainted snail tissues.