The influence of environmental temperature upon transmission of the cercariae of Echinostoma liei (Digenea: Echinostomatidae)

Abstract

The survival and infectivity characteristics of the cercariae of Echinostoma liei are described for 6 different water temperatures in the range 12–40 °C. Cercarial survival steadily decreased with increasing temperature, the maximum survival time falling from 75 h at 12 °C to approximately 8 h at 40 °C. Changes in environmental temperature affected the infectivity even of freshly emitted cercariae but their most noticeable effect was upon the rate at which infectivity diminished with increasing cercarial age. Infectivity rose from zero at 12 °C to a maximum at 30 °C before declining to a low level at 40 °C. The transmission efficiency of the cercariae at each temperature was calculated as the ratio of the instantaneous per capita rates of mortality and infection respectively. The efficiency of transmission was high between 19 and 30 °C, suggesting that cercariae are well adapted for transmission at water temperatures likely to be encountered in natural habitats.