People are infected when they swallow cysts containing fluke larvae in raw, undercooked, dried, salted, or pickled freshwater fish or on contaminated watercress.
Depending on the infecting species and intensity of infection, people may have fever, chills, abdominal discomfort or pain, jaundice, itching, diarrhea, and weight loss.
Doctors diagnose the infection when they see fluke eggs in a person's stool or in the contents of the intestine.
Depending on the type of fluke, drugs such as praziquantel, albendazole, or triclabendazole can eliminate them.
Flukes are parasitic flatworms. There are many species of flukes. Different species tend to infect different parts of the body. Liver fluke infections occur in Europe, Africa, eastern Asia, and South America but are rare in the United States. (See also Overview of Parasitic Infections.)
Flukes that cause infections of the liver include
Clonorchis sinensis (Chinese or oriental liver fluke), which causes clonorchiasis
Opisthorchis viverrini (Southeast Asian liver fluke) and O. felineus (cat liver fluke), which cause an infection that resembles clonorchiasis
Fasciola hepatica (the common liver fluke or sheep liver fluke), which causes fascioliasis and typically infects sheep and cattle
The life cycle of flukes is complex. People can get liver fluke infections when they swallow cysts containing immature flukes (larvae) of the following:
Clonorchis sinensis and Opisthorchis in raw, undercooked, dried, salted, or pickled freshwater fish; Clonorchis sinensis also sometimes in freshwater shrimp
Fasciola hepatica or Fasciola gigantica in cysts on watercress or other water plants growing in water contaminated by eggs in sheep or cattle dung
After the cysts of Clonorchis sinensis and Opisthorchis are swallowed, the larvae leave the cysts in the intestines and travel back up the intestine and enter the bile duct (the tube that carries bile from the liver and gallbladder to the intestine). Then they go up the bile duct into the liver or sometimes the gallbladder. There, they develop into adults and produce eggs. Adults can live 20 to 30 years if untreated. Eggs are passed in the stool and ingested by snails. Infected snails release immature flukes that can swim (called cercariae). Cercariae released from infected snails form cysts in various freshwater fish or shrimp.
After the cysts of Fasciola hepatica or Fasciola gigantica are swallowed, they reach the intestine and release immature larvae. The larvae move through the wall of the intestine into the abdominal cavity and liver, then to the bile ducts. There, they develop into adult flukes, which produce eggs. Eggs are passed in stool. In water, the eggs release larvae, which penetrate snails. Infected snails release immature flukes (cercariae), which form cysts on watercress and other water plants.
At first, liver flukes may cause no symptoms, or depending on the type and severity of the infection, they may cause fever, chills, abdominal pain, liver enlargement, nausea, vomiting, and hives. Fasciola flukes are more likely to cause these symptoms.
Over time, if adult flukes block enough of the bile duct inside or outside the liver, people may develop yellowing of the skin and whites of the eyes (jaundice), itching, diarrhea, and weight loss. Sometimes the flukes damage the liver, causing scarring (fibrosis). Other complications include bacterial infections of the bile ducts, gallstones, and pancreatitis.
Occasionally, liver flukes infect the wall of the intestine, the lungs, the skin, or the throat.
Years later, infected people may develop cancer of the biliary ducts (cholangiocarcinoma). This cancer has occurred in Vietnam veterans, who may have eaten raw or undercooked fresh water fish carrying liver flukes while serving in Southeast Asia. Whether liver fluke infection contributed to the cancer's development in Vietnam veterans is uncertain.
Doctors diagnose Clonorchis, Opisthorchis, or Fasciola infections when they see fluke eggs in a person's stool (feces) or in the contents of the person's intestines. However, finding eggs in stool may be difficult.
In the early stages of Fasciola hepatica infection, blood tests can be done to check for antibodies to the flukes. Antibodies may be detected in blood weeks before eggs are present in the stool. (Antibodies are proteins produced by the immune system to help defend the body against attack, including that by parasites.) Tests are also done to measure levels of eosinophils (a type of white blood cell) in the blood. The number of eosinophils may increase in people with a fluke infection.
Imaging tests of the liver, such as ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), endoscopic retrograde cholangiopancreatography (ERCP), or cholangiography, may be done to check for damage to the liver and bile ducts. Occasionally, doctors see adult flukes in the bile duct when they examine the inside of the digestive tract with a viewing tube (endoscope) passed through the mouth.
Thoroughly cooking freshwater fish or shrimp from areas where Clonorchis and Opisthorchis infections occur helps prevent liver fluke infections. Raw, dried, salted, or pickled freshwater fish or shrimp from these areas should not be eaten. Raw watercress and other water plants should not be eaten in areas where sheep or cattle may be infected with Fasciola.
Liver fluke infections are treated with a drug that eliminates flukes from the body. These drugs include
If the flukes block the bile ducts, surgery may be necessary.