Fascioliasis (Fasciola Infection)
Fascioliasis is an infectious disease caused by the trematodes Fasciola gigantica and the Fasciola hepatica. The Fasciola flatworms are parasites that are carried by herbivores which can infect humans.
The lifecycle of the Fasciola parasites begin as immature eggs that discharge into the biliary ducts and then the stool. When expelled into water, the eggs are embryonated and release miracidia. The miracidia enter snails. Appropriate snail hosts include a number of species from the genus Lymnae. The snails act as intermediate hosts while the miracidia mature into cercariae. The cercariae leave the snails for water plants and various aquatic surfaces to encyst as metacercariae. When mammals consume aquatic plants with the metacercariae, they become infected. Human infection occurs from accidental ingestion of metacercariae from freshwater plants such as watercress.
Inside the mammal host, the metacercariae excyst in the duodenum, traveling to the wall of the intestines, the peritoneal cavity, as well as the parenchyma of the liver into the biliary ducts. There, the metacercariae mature into adulthood. Full maturation may take up to four months inside a human host. The fasciola hepatica favors herbivore hosts but can infect a multitude of animals.
Fascioliasis is found all over the world. Infections with Fasciola hepatica are common to areas with cattle and sheep farming and areas where watercress is eaten. Such areas may include Asia, Europe, and the Middle East. Fasciola gigantica infection can impact Hawaii, Asia, and Africa.
Symptoms of the acute phase of Fascioliasis include hepatomegaly, diarrhea, eosinophilia, abdominal pain, fever, urticaria, and vomiting. Such symptoms can last for months and are caused by the movement of the immature flatworms through the hepatic parenchyma. During the chronic phase of the disease, symptoms may include inflammation as well as biliary obstruction. At this stage, symptoms can be harder to detect but ectopic locations of infections can occur. Common areas include the lungs, the intestinal wall, pharyngeal mucosa, and subcutaneous tissue.
Diagnosis of Fascioliasis requires microscopy to identify eggs during the chronic stage of the disease. Stool samples may be required or samples from biliary or duodenal drainage. The eggs are identical to those of the Fasciolopsis buski. Eggs may be present in stool but rather than from infection, the cause may be the consumption of infected livers with eggs in them. This is known as False Fascioliasis or Pseudofascioliasis. Misdiagnosis can be prevented by not consuming liver before a stool exam. During the earlier stages of the disease, antibody detection can also be used. Treatment for Fascioliasis includes the drugs triclabendazole or bithionol. Praziquantel, which is helpful against other Fasciola infections, may not work on Fasciola hepatica infections.