Some adult flukes occupy various sites in the biliary system and liver. These include Fasciola hepatica, Clonorchis spp. ,and Opistorchis spp. Their life cycles are very similar to those living in the intestinal tract. The image to the right (top) depicts the life cycle of Fasciola hepatica. Similar to the intestinal trematodes, the metacercaria larvae also encyst on aquatic vegetation. Humans are not the only hosts of this organism; ruminants commonly get Fasciola. The Clonorchis life cycle differs in that the metacercariae usually encyst on fish, and humans get it from eating undercooked fish.
A similar life cycle seen on the bottom right is exhibited by Paragonimus spp. However, the adult lives in the parenchyma of the lungs, and can often stray to other organs or sites in the body. Another exception is that once the metacercariae are swallowed, they must migrate from the intestines across the diaphragm and into the lungs. Although it lives in the lungs, the eggs can sometimes be seen in the feces when sputum is coughed up and swallowed. Thus, the specimen of choice is sputum. A direct examination of the sputum is often used when Paragonimus is suspected.
