Excystation and infectivity of Echinostoma caproni metacercariae after prolonged storage

This study examined excystation and infectivity of Echinostoma caproni Rich ard, 1964, metacercariae stored in Locke's solution 1:1 at 4 degreesC for u p to 12 mo or maintained in Biomphalaria glabrata (Say, 1816) snails for 3 mo. Comparisons were made with fresh encysted metacercariae obtained from B . glabrata within 14 d postinfection. Excystation was scored as the number of excysted metacercariae obtained after cyst treatment for 1 hr at 41 +/- 1 degreesC in an Earle's alkaline solution with trypsin-bile salts. The per centage excystation in trials with fresh cysts was 98.3% compared with 51.5 % for cysts stored in Locke's solution for 5 mo. Cysts stored for 8 or 12 m o did not excyst. The percentage of worm recovery in mice fed fresh cysts w as 66% compared with 13.5% in mice fed cysts stored for 5 mo. The percentag e of worm recovery in mice fed cysts that had been maintained in B. glabrat a for 3 mo was 75%. Some experiments were done with mice fed excysted metac ercariae. The percentage of worm recovery in mice fed excysted metacercaria e from fresh cysts was 44% compared with 13% in mice fed excysted metacerca riae from cysts stored in Locke's solution for 5 mo. Implications of these findings for the maintenance of encysted metacercariae of E. caproni in the laboratory are discussed.