The flukes living in the intestinal tract include Fasciolopsis buski, Heterophyes and Metaganimus spp., and Nanophyetus salmoncola. Also, there are several species of the genus Echinostoma which can be found in the small intestine.
As mentioned previously, all flukes have a snail as an intermediate host. This snail lives in the water, so water is also a common theme in the lives of the flukes. The image to the right shows the life cycle of F. buski, but the other intestinal flukes are similar, differing only in the second intermediate host or other site where the definitive host acquires the metacercarial form. Their life cycles can be summarized as the following:
1. Eggs are released into the water.
2. Eggs release a larval form known as miracidium. The miracidia (pl.) invade a specific snail host (Each species has its own snail host species.)
3. Within the snail, three larval forms mature: sporocysts - rediae - cercariae.
4. The cercariae exit the snail and encyst as metacercariae on either aquatic vegetation or fish.
5. The mammalian host (human in these cases) ingests the metacercariae while eating the plant or fish.
6. The metacercariae excyst in the intestinal tract, attach via suckers and grow into an adult. The adults are hermaphroditic and produce eggs which are then found in the feces.
