Antagonism of Echinostoma liei (Trematoda: Echinostomatidae) against the trematodes Paryphostomum segregatum and Schistosoma mansoni

Abstract

Echinostoma liei, a newly described 37-spined eehinostome from Egypt, was tested against two trematodes in paired infections in the snail host, Biomphalaria glabrata (NIH strain). E. liei, when matched with the highly predacious Brazilian echinostome Paryphostomum segregatum, was dominated by the latter's predatory rediae. Pre-existing E. liei infections were destroyed, although the P. segregatum infection was itself delayed in development by an unidentified ‘indirect antagonism’ elicited by the E. liei larvae. In concurrent exposures with the two species, or with E. liei challenge of an established P. segregatum infection, the E. liei miracidia penetrated the snail, but the infection did not become established. When E. liei and S. mansoni were paired, the former species dominated. Exposure of snails already infected with E. liei to miracidia of S. mansoni slowed growth of the latter and the schistosome sporocysts eventually disintegrated without producing cercariae. When E. liei miracidia were exposed to snails with S. mansoni infections of different ages, the echinostome became established but developed slowly. Subsequently, however, it destroyed the schistosome infection. Although E. liei is itself quickly eliminated by P. segregatum, the two species appear almost equal in anti-schistosome capacity. This can be credited in part to a deleterious or lethal effect of the E. liei-schistosome combination on the host snail, as well as to a direct anti-schistosomal effect. Greater knowledge of this host-inter-trematode balance may permit the use of trematodes to attack infected snails and their parasites in regions hyperendemic with human schistosomiasis.

Photoperiodic cercarial emergence patterns of the digeneans Echinoparyphium recurvatum and Plagiorchis sp. from a mixed infection in Lymnaea peregra

“…However, the observation is interestingly consistent with the well documented strongly antagonistic influence that the rediae of echinostomes (and those of the cathaemasid R. marini) have on other digeneans within the same host mollusc; particularly those having only sporocyst generations. The markedly antagonistic effects of rediae of echinostomes such as Paryphostomum radiatum and Echinostoma liei on larval schistosomes within the same host mollusc have been noted in detail by Heyneman et al (1972), Lie (1967) and Combes (1982). Køie (1987) has published excellent scanning electronmicrographs of a cannibalistic redia of the echinostome Mesorchis denticulatus.…”

COMMUNITY STRUCTURE: Larval Trematodes in Snail Hosts

“…Other studies by Lie, Heyneman and co-workers (44,68) established that prior infections altered the susceptibility of such snails to subsequent parasitization by other trematode species. However, rather than decreasing the likelihood of a second infection (interspecific heterologous immunity), these changes in snail defensive capabilities increase the likelihood of subsequent infections (44). Indeed, Austrobilharzia terrigalensis is an obligate secondary invader (113).…”

“…Further, one form of heterogeneity that we have not been able to assess is the repeatedly documented differential high susceptibility of previously infected snails (e.g. 44,69). This source of heterogeneity could greatly intensify the expected frequency of multiple infections.…”

Differential Parasitism of Native and Introduced Snails: Replacement of a Parasite Fauna

“…The effects on second intermediate hosts generally depend on the number of infections. Second intermediate hosts often experience a decrease in growth rate and survivorship Heyneman et al 1972;Kuris and Warren 1980) and often suffer increased susceptibility to predation (Holmes and Bethel 1972;Lafferty and Morris 1996;Lafferty 1999). One trematode species, Acanthoparyphium spinulosum, infects C. californica, by using it as both a first and second intermediate hosts.…”