Effects of temperature on survival, infectivity and in vitro encystment of the cercariae of Echinostoma caproni

The effects of temperature on survival, infectivity and in vitro encystment of Echinostoma caproni cercariae in artificial spring water (ASW) were studied. Effects of aging cercariae in ASW at various temperatures showed that at 23degreesC cercariae achieved 50% survival in 24 h, compared to 92 h at 12degreesC. Cercariae aged in ASW at 28 and 37.5degreesC showed 50% survival at 16 and 10 h, respectively. Cercariae aged at different temperatures for various times were used to infect juvenile Helisoma trivolvis (Colorado strain) snails maintained in ASW at 23degreesC. Index of infectivity was based on counting encysted metacercariae in the snails at 8 to 12 h post-infection. Cercariae aged at 23, 28 and 37.5degreesC showed 50% encystment at 6, 8 and 4 h, respectively. Cercariae aged at 4degreesC showed 50% encystment in 10 h and cercariae aged at 12degreesC showed 50% encystment beyond 16 h. Cercariae showed maximal longevity and infectivity in snails when aged at 12degreesC in ASW. For E. caproni, as in other digeneans, the infective period of cercariae is markedly shorter than the maximal life-span at any given temperature. Studies on in vitro encystment of E. caproni cercariae in Locke's solution:ASW (1:1) showed that encystment was optimal at 23degreesC (78% encystment) and that it declined to 44% at 28degreesC and became almost nil (0.02%) at 12 or 37.5degreesC.