Studies on Echinostomatidae (Trematoda) in Malaya. XII. Antagonism between Two Species of Echinostome Trematodes in the Same Lymnaeid Snail

Abstract

Four species of echinostome trematodes are fairly common in Lymnaea rubiginosa from rice fields in central Malaya, but none of these snails has been found infected with more than one echinostome species. Naturally infected snails shedding cercariae of one species were exposed to miracidia of a different species. Only three (5%) of 65 surviving field snails could be infected with a second species, whereas 40 (89%) of 45 laboratory-reared control snails acquired the infection when exposed in the same containers. Failure of the second species to develop is the result either of immune responses or of direct action between existing echinostome rediae and new invading sporocysts similar to that known to occur between echinostome rediae and sporocysts of various unrelated trematodes. Although it is well known that snails in nature may be infected with more than one species of trematode, several authors (Cort et al., 1937; Martin, 1955) have commented upon the relative rarity with which echinostome infections are found in combination with others. Recently, we have shown (Lie et al., 1965) that antagonistic interaction occurs when echinostome infections are experimentally induced in snails already harboring strigeid, plagiorchiid, or schistosome larvae. Similar interaction has also been observed (Lie, 1966) between sporocysts of Schistosoma mansoni (Sambon) and rediae of an unidentified Echinostoma species in the snail Australorbis glabratus (Say). This paper is a report on attempts to infect single snails with two species of echinostomes.