The trematode flatworm parasite Fasciolopsis buski is the largest intestinal fluke of humans. Fasciolopsis buski is found in Asia and the Indian subcontinent, especially in areas where humans raise pigs and consume freshwater plants.
Immature eggs are discharged into the intestine and stool. Eggs become embryonated in water and release miracidia, which invade a suitable snail intermediate host. In the snail, the parasites undergo several developmental stages: sporocyst, redia, and cercaria. The cercariae are released from the snail and encyst as metacercariae on aquatic plants. The mammalian hosts become infected by ingesting metacercariae on the aquatic plants. After ingestion, the metacercariae excyst in the duodenum and attach to the intestinal wall. There they develop into adult flukes (20 to 75 mm by 8 to 20 mm) in approximately 3 months, attached to the intestinal wall of the mammalian hosts (humans and pigs). The adults have a life span of about one year. Mas-Coma et al. (2005) reviewed the biology, diagnosis, treatment, and epidemiology of fasciolopsiasis (Mas-Coma et al. 2005 and references therein).
Fasciolopsis buski is one of the largest digenean trematode flatworms infecting humans. Pigs are the only important reservoir. Fasciolopsiasis (infection with Fasciolopsis) is present in many Asian countries. Fasciolopsis buski produces a large number of eggs in humans (13,000 to 26,000, mean 16,000/worm per day). Snail hosts are limited to small planorbids of the genera Segmentina, Hippeutis, and Gyraulus. Aquatic plants eaten by humans that may help transfer F. buski include water caltrop (Trapa natans in China, Trapa bispinosa in Taiwan, and Trapa bicornis in Bangladesh and Thailand), water chestnut (Eliocharis tuberosa), water hyacinth (Eichhornia spp.), water bamboo (Zizania spp.), water lotus (Nymphaea lotus), water lily (Nymphaea spp.), watercress (Nasturtium officinale), gankola (Otelia spp.), and water morning glory (Ipomoea aquatica). Metacercarial cysts on plants are visible to the naked eye. Up to 200 cysts may be found on the surface of one water caltrop, but the usual number is about 15 to 20. Cercariae may also encyst on the water surface. (Mas-Coma et al. 2005; Chai et al. 2009)