a helminthiasis of man and animals caused by trematodes. In man, the causative agents of trematodiases parasitize the liver, pancreas, intestines, lungs, and blood, causing various disorders. Infection usually occurs after swallowing trematode larvae with water or food. Opisthorchiasis and meta-gonimiasis are contracted by consuming infested fish, paragonimiasis by consuming infested crabs and freshwater crustaceans, and fascioliasis by consuming infested water and plants. Schisto-somiasis is contracted when the larvae of the parasites penetrate the skin during bathing.

Opisthorchiasis is found most often in Western Siberia, while paragonimiasis and metagonimiasis occur in the Far East, and schistosomiasis in tropical countries.

Treatment depends on the species of trematode. Preventive measures consist in protecting the external environment from contamination by sewage, observing rules of personal hygiene, and avoiding undercooked fish and crustaceans.

Trematodiases in animals are caused by approximately 125 species of trematodes that parasitize various organs and systems of all species of wild and domestic animals, including livestock and other vertebrates. Trematodes are distributed throughout the world. As a result of trematodiases, the growth of young animals is retarded and the quality of the livestock’s meat is lowered. It is necessary to destroy parasitized organs of infested animals, such as the liver and lungs, when the animals are slaughtered. In addition, plagues may break out among the animals. The greatest harm is caused by fascioliasis, dicroceliasis, and schistosomiasis japónica of sheep and cattle; echinochasmia-sis of swine; paramphistomiases of ruminants; prosthogonimiasis of chickens; and echinostomiases of poultry, caused by various species of trematodes.

Symptoms depend on the localization of the parasites in the body of the host, for example, the intestines, liver, pancreas, respiratory organs, or circulatory or genital systems. Treatment consists in the administration of antihelminthics. The main preventive measure is the control of mollusks, the intermediate hosts of trematodes, by means of the reclamation and periodic rotation of pastures.