Echinostomiasis--a snail-borne intestinal trematode zoonosis.

Numerous echinostome trematodes are found in the intestines of birds and mammals throughout the world, and echinostomiasis in humans has been attributed to approximately 16 different species. In humans it is usually regarded as a rare intestinal parasite of little clinical importance except in heavy infections. Diagnosis of echinostomiasis is made by identification of eggs during fecal examination; however, speciation of echinostomes requires morphological study of adult worms following anthelminthic treatment. The complex life cycles of echinostomes are all linked to freshwater habitats. A mammalian or avian definitive host, one or two molluscan hosts, and one or two freshwater stages are usually required to complete the life cycle. In addition, amphibians and fish have been implicated in the transmission of some species. Prevention of human cases is dependent on eating habits, since raw or insufficiently cooked molluses, and to a lesser extent fish and amphibians, are sources of infection for humans. Human cases have been effectively, albeit accidentally, controlled by the introduction of fish which prey on the larval stages of the essential molluscan hosts.