Chapter 1. The biology of the caecal trematode Zygocotyle lunata

This chapter examines the significant studies on the caecal paramphistomid Zygocotyle lunata from mainly 1941 to 2008. This digenean is one of two paramphistomid species in the family Zygocotylidae. Z. lunata has an almost global distribution being found in the wild in numerous waterfowl and various species of ruminants. It infects planorbid snails in the genera Helisoma and Biomphalaria. Because it may involve concurrent infections with Schistosoma mansoni in species of Biomphalaria snails, there is an interest in Z. lunata as a potential control agent against S. mansoni. Z. lunata may have some impact as a pathogen of birds in wildlife diseases, but its real assessment in this role is not fully understood. The cercariae of this paramphistomid when released from snails encyst on a substratum such as vegetation or the shells of aquatic invertebrates in the wild or in the laboratory on the glass or plastic of a container holding the snails. Most studies on the intra-molluscan parasitic stages are based on work from snails collected in the wild and experimental studies using laboratory-reared snails are sparse. Numerous experimental mammalian and avian hosts can be infected with the metacercarial cysts of this digenean, but quantitative experimental studies on the adult stages of this parasite using known numbers of cysts and well-defined strains of vertebrate hosts are sparse. Likewise, some studies on the immunology and pathology of this trematode have been done, but for the most part they are fragmentary and do not provide quantitative information on these topics. Published information on the molecular biology of this organism does not exist. The organism is in need of new research efforts at all levels of organization from the molecular to the community.