fluke

Common name for members of the class Trematoda (phylum Platyhelminthes). All flukes of mammals (subclass Digenea) are internal parasites in the adult stage and are characterized by complex digenetic life cycles involving a snail initial host, in which larval multiplication occurs, and the release of swimming larvae (cercariae), which directly penetrate the skin of the final host (as in schistosomes), encyst on vegetation (as in Fasciola), or encyst in or on another intermediate host (as in Clonorchis and other fish-borne flukes). Flukes of lower vertebrates (order Monogenea), especially fish, are frequently monogenetic ectoparasites or gill parasites. Blood flukes live in the mesenteric-portal bloodstream and associated vesical and pelvic venous plexuses; they include Schistosoma haematobium (the vesical blood f.), S. mansoni (Manson intestinal blood f.), and S. japonicum (the Oriental blood f.). Other important flukes are Paragonimus westermani (bronchial or lung f.), Opisthorchis felineus (cat liver f.), Clonorchis sinensis (Chinese liver or Oriental f.), Heterophyes heterophyes (Egyptian or small intestinal f.), Fasciolopsis buski (large intestinal f.), Dicrocoelium dendriticum (lancet f.), Fasciola hepatica (liver or sheep liver f.), and Paramphistomum (rumen f.). [A.S. floc, flatfish]

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fluke 'flük n a flattened digenetic trematode worm broadly TREMATODE see LIVER FLUKE

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n.

any of the parasitic flatworms belonging to the group Trematoda. Adult flukes, which have suckers for attachment to their host, are parasites of humans, occurring in the liver (liver flukes; see Fasciola), lungs (see Paragonimus), gut (see Heterophyes), and blood vessels (blood flukes; see Schistosoma) and often cause serious disease. Eggs, passed out with the stools, hatch into larvae called miracidium, which penetrate an intermediate snail host. Miracidia give rise asexually to redia larvae and finally cercaria in the snail's tissues. The released cercariae may enter a second intermediate host (such as a fish or crustacean); form a cyst (metacercaria) on vegetation; or directly penetrate the human skin.

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(flk) trematode.