REVIEW The use of echinostomes to study host–parasite relationships between larval trematodes and invertebrate and cold-blooded vertebrate hosts Rafael Toledo & Carla Muñoz-Antoli & Bernard Fried Received: 10 January 2007 / Accepted: 17 January 2007 / Published online: 6 February 2007 # Springer-Verlag 2007 Abstract Echinostomes are intestinal trematodes with life cycles that are easy and inexpensive to maintain in the laboratory. For this reason, echinostomes have served for years as experimental models in different areas of parasi- tology. However, the usefulness of these trematodes in experimental parasitology has been under estimated. In this paper, we discuss the life cycles of echinostomes and the techniques used to maintain them in the laboratory. We further examine the characteristics of these trematodes that make them useful models for the analysis of larval parasite– host relationships. Echinostomes are useful for studies on the immunobiology of snails, host-finding processes of free-living larval stages, effects of larval trematode infec- tions on anuran populations, and studies on analytes in the larval trematodes and their snail intermediate hosts. Introduction Echinostomes are cosmopolitan intestinal parasitic flat- worms that invade man, domestic animals, and wildlife, and also parasitize, in their larval stages, numerous inverte- brate and cold-blooded vertebrate hosts. The life cycle of echinostomes is easy to maintain in the laboratory as larval and adult worm stages, and they have been extensively used as experimental models at all levels of organization, from the molecular to the organismic. Of particular interest is the fact that echinostomes often share some intermediate hosts with other trematodes of greater medical importance. Echinos- tomes have been used in experiments on excystation and in vitro cultivation, larval parasite–host relationships, host– parasite recognition processes, and several aspects of adult parasite–host relationships among other aspects of parasi- tology. Echinostomes (and particularly the members of the genus Echinostoma) have contributed significantly to developments in different areas of parasitology. However, their biological characteristics show that further use of these trematodes as experimental models may enable us to increase our knowledge of various aspects of the host– parasite relationships. In this paper, we analyze the use of the echinostomes for studies on the host–parasite interactions between larval trematodes and invertebrate and cold-blooded vertebrate hosts, with an emphasis on those aspects that may be important for trematodiasis of medical interest such as schistosomiasis. In this context, we briefly describe the life cycle of echinostomes and the techniques for their maintenance in the laboratory. Moreover, we review in detail some studies in which echinostomes are important to gain further insight in host–parasite interactions of larval trematodes and their intermediate hosts. Life cycle of the echinostomes Echinostome adults are cosmopolitan hermaphroditic dige- neans that live in the intestine and bile ducts of numerous vertebrate hosts, particularly aquatic or semi-aquatic birds and mammals. In the wild, the life cycle of an echinostome using intermediate and definite hosts associated with fresh water is maintained when a definitive host releases eggs into Parasitol Res (2007) 100:1177–1185 DOI 10.1007/s00436-007-0470-6 R. Toledo (*) : C. Muñoz-Antoli Departamento de Parasitología, Facultad de Farmacia, Universidad de Valencia, Av. Vicente Andrés Estellés s/n, 46100 Burjassot, Valencia, Spain e-mail: rafael.toledo@uv.es B. Fried Department of Biology, Lafayette College, Easton, PA 18042, USA