Maintenance of Helisoma trivolvis naturally infected with Echinostoma trivolvis in spring water at 4 degrees C for 300 days.

Helisoma trivolvis (Pennsylvania strain) snails naturally infected with Echinostoma trivolvis larvae were maintained for 10 months (300 days) at 4 degrees C in artificial spring water to determine the effects of storage on parasite survival. Three of 20 snails were alive at 10 months and when isolated in spring water at 22-24 degrees C released active cercariae. The mean number of cercariae released in 2 h from each stored snail was significantly less than that from freshly collected snails. Infectivity of cercariae from stored hosts to experimentally infected, laboratory-raised Helisoma trivolvis (Colorado strain) snails was significantly less than that of cercariae from fresh hosts based on cyst recoveries in the Colorado strain of H. trivolvis within 24 h p.i. There was no significant difference in the redial number or the number of cercariae per redia in stored versus fresh snails. In conclusion, some reduction in cercarial emergence and decrease in cercarial infectivity to a second intermediate snail host occurred following storage of H. trivolvis naturally infected with E. trivolvis in ASW at 4 degrees C for 10 months.