The Life Cycle of a Liver Fluke in a Human

By Michelle Rosa Raybeck
Liver flukes can enter the human body through raw fish.
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Liver flukes are flat worms that take up residence in the human liver. They suck blood, lay eggs and grow until they begin to cause potentially serious health problems. These parasites have a complex life cycle in which they pass through several intermediate hosts before being ingested and lodging in the a human.

Trematodes

Liver flukes are trematodes, a class of flat-bodied parasitic worms. In general, the life cycle begins as an egg. Even one egg can spawn hundreds of immature flukes (miracidia). Snails ingest the eggs, which then hatch inside the snail's gut; the miracidia burrow out and swim freely as cercaria.

Intermediate Host

The cercaria of the fluke Clonorchis sinensis, also known as the Chinese liver fluke, burrow through a fish's skin. Within the fish's tissues they become enclosed in a cyst and remain there as metacercaria. If the fish is ingested raw or undercooked, the metacercaria get into the stomach and intestine, where gastric juices release them from their cysts. Then they migrate through the stomach wall, into the liver and take up residence in the bile ducts, where they mature into flukes. In parts of the world where raw fish is a major component of the local diet, the majority of people have flukes, but of these, only about a quarter develop health problems.

Fasciola Hepatica

The large liver fluke, fasciola hepatica, gets into the human digestive system through certain water vegetables such as cress and water chestnuts. Fasciola hepatica can grow to 13 mm by 30 mm and can easily and intermittently block the bile ducts. Liver flukes can live and multiply inside the human liver for as long as 30 years. Their eggs pass out of the body in feces; the number of eggs per gram of feces is one way in which doctors determine the severity of a liver fluke infection.

Health Problems

Liver flukes cause digestive and liver symptoms, including vomiting, diarrhea, jaundice (yellowing of the eyes and skin), enlarged liver, liver stones, abdominal pain and may cause internal infections. Liver flukes have also been linked with certain types of liver cancer. The problems become chronic once the flukes reach their mature stage. Many people just live with the symptoms until they are sick enough to seek treatment, in which case there may be lasting complications associated with liver disease and liver cancer. A prescription medication called Praziquantel may kill the flukes before they can do lasting damage. Adult flukes do not leave the body; they just do lasting tissue damage.

Treatment

Good sanitary habits are the best way to prevent parasites, but if you do contract liver flukes, you must do a thorough cleaning of your home and other environments. You and your entire family must be treated. The purpose of all this sanitation and family treatment is to prevent the eggs and cysts from spreading to other hosts. Besides Praziquantel, your doctor has an array of prescription antiparasitic medications among which to choose. Always tell your doctor what medications and dietary supplements you are taking in order to avoid drug interactions.