Mmmh. Intestinal fluke worms....
This the largest of the various fluke worms that can infect the human intestine and can be found mainly in South East Asia. Ingestion happens mostly by the peeling of edible water plants with the teeth, especially the water caltrop and the water chestnut.
After the eggs are swallowed, the metacercaria (or larvae) slips out of its cystic cover and starts growing while being attached to your duodenum, taking about 3 months until it reaches its adult size of ca 7.5 cm.
The infection is most likely to be acquired in areas were pig and human faeces (mmmh...) are allowed to enter water that is used for human consumption, and the easiest way to avoid infection is boiling the water you drink or peeling fruits with your hands before eating them.
The classic signs of an infection with Fasciolopsis are having something wriggly in your poo, followed by a bout of diarrhoea. Very rarely this can end in intestinal obstruction or oedema due to protein loss.
In your gut the adult worm will produce eggs which back in the water will embryonate into miracidia, which will infect a suitable snail. During their time in a snail they will grow up into the metacercaria that will be released back into the water and swallowed by that tourist buying those nice fresh water chestnuts from that nice man behind the stall in northern vietnam.
Treatment is easy with a single dose of Praziquantl 15mg/kg
Nature. It can be quite yucky, ay?
Dion R. Bell, Tropical Diseases, 4th Edition, Blackwell Science, Pp 246 - 247