Experimental studies on the transmission dynamics of the cercariae of Echinoparyphium recurvatum (Digenea: Echinostomatidae)

SUMMARY Age-dependent survival and infectivity characteristics are described for the cercariae of Echinoparyphium recurvatum. At 18 °C the maximum life-span of the cercariae was 48 h and 50% survival occurred at 30·5 h. Infectivity of cercariae to the second intermediate host, Lymnaea peregra was maximal approximately 2 h after emission from the first intermediate host and it subsequently declined to zero at 19 h. It is suggested that the period of sub-maximal infectivity at the beginning of the cercarial life-span may represent a phase during which dispersal is an important function of the larvae. The relationship between infective stage density and establishment success was linear up to densities equivalent to 5000 cercariae/1. At higher cercarial densities the proportion of parasites establishing in second intermediate hosts declined progressively with increasing cercarial density. The mean number of parasites establishing/host increased linearly with increasing host size.