Trematodes

Background

Microbiology

• Trematodes (flukes) are platyhelminths
• All have an intermediate snail host, and most have a second intermediate host before reaching humans via ingestion of the intermediate

Organism	First intermediate	Second intermediate	Distribution
Blood flukes
Schistosoma haematobium	Bulinus species	none; penetrates skin	Africa and the Middle East
Schistosoma intercalatum	Bulinus species		Central and West Africa
Schistosoma japonicum	Oncomelania species		Asia
Schistosoma mansoni	Biomphalaria species		Africa, the Middle East, and South America
Schistosoma mekongi	Neotricula species		Southeast Asia
Intestinal flukes
Echinostoma ilocanum		snails and fish	Middle and Far East
Fasciolopsis buski		water vegetables, especially watercress, bamboo, and water chestnuts	China, Thailand, India, Bangladesh, with pig reservoir
Heterphyes heterophyes		fresh-/brackish-water fish	Middle and Far East
Metagonimus yokogawai		fish	Middle and Far East
Liver flukes
Clonorchis sinensis (Chinese liver fluke)		fish	China, South Korea, Japan, Vietnam, and eastern Russia; common
Dicrocoelium dendriticum (lancet liver fluke)
Fasciola gigantica		underwater vegetation	Africa, Hawaii, western Pacific, Southeast Asia
Fasciola hepatica (sheep liver fluke)	Lymnaea species	underwater vegetation, especially watercress	Bolivia and Peru, but also Europe, South America, and Middle East, near sheep rearing areas
Metorchis conjunctus (Canadian liver fluke)
Opisthorchis felineus			Western Europe and Siberia
Opisthorchis viverrini (Southeast Asian liver fluke)		freshwater fish	Southeast Asia
Lung flukes
Paragonimus westermani	Semisulcospira species	seafood, especially crayfish or crab	China, Japan, Korea, the Philippines, and Thailand