What are Liver flukes?
Liver flukes are parasitic flatworms that infect the liver and bile ducts. The main liver flukes that infect humans belong to the genera Clonorchis, Opisthorchis and Fasciola. They have different geographic distributions and are acquired through different foods.
Clonorchis and Opisthorchis are mainly acquired by eating raw or undercooked freshwater fish containing the parasite's larvae. Fasciola, which causes fascioliasis, is usually acquired by eating raw freshwater plants such as watercress contaminated with parasite larvae, or through contaminated water.
Liver fluke infections occur mainly in parts of Asia, Africa, Latin America and other areas where the parasites' animal hosts and freshwater environments are present. The World Health Organization (WHO) estimates that at least 2.4 million people are infected with fascioliasis in more than 70 countries worldwide, with several million more people at risk.
For Australian travellers, infection is most relevant when travelling in endemic areas and eating raw or inadequately cooked freshwater fish or uncooked freshwater plants. Chronic infection with Clonorchis sinensis or Opisthorchis viverrini can cause long-term inflammation and damage to the bile ducts and is associated with an increased risk of bile duct cancer, referred to as a cholangiocarcinoma.
FAQs
Can I get liver flukes from eating sushi?
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The risk depends on the type of fish and where it comes from. Liver flukes such as Clonorchis and Opisthorchis are associated specifically with freshwater fish, rather than marine fish. Raw, lightly salted, smoked or pickled freshwater fish can still contain infectious parasites.
Which destinations are most relevant for Australian travellers?
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Clonorchis species occur mainly in parts of China, Korea, Taiwan and northern Vietnam, while Opisthorchis viverrini occurs mainly in northeast Thailand, Laos, Cambodia and parts of Vietnam. Opisthorchis felineus occurs in parts of Europe and Russia. Fasciola has a much wider distribution, including parts of Latin America, the Middle East and other regions.
I ate raw freshwater fish overseas. Do I need a test?
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Not necessarily. Routine testing is not recommended for people without symptoms simply because they have travelled to an endemic area. However, tell your doctor about the exposure if you develop persistent abdominal symptoms, jaundice or other compatible symptoms after travel.
Can liver flukes cause cancer?
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Some long-term infections with Clonorchis sinensis and Opisthorchis viverrini are associated with an increased risk of cholangiocarcinoma, a cancer of the bile ducts. This is a complication of chronic infection rather than a common outcome for travellers.
Is there a vaccine available for liver flukes?
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There is currently no vaccine available to prevent liver fluke infection in humans. Travellers can reduce their risk by avoiding raw or undercooked freshwater fish and uncooked freshwater plants in areas where liver flukes occur.
What to Know
Symptoms of Liver flukes
Many liver fluke infections cause no symptoms, particularly when the number of parasites is small. When symptoms occur, they can include indigestion, nausea, abdominal pain, diarrhoea, constipation, fever, an enlarged liver and jaundice. Symptoms may result from inflammation or blockage of the bile ducts.
Fasciola infection can cause an acute illness with fever, abdominal pain, nausea, vomiting, an enlarged liver and abnormal liver tests. Symptoms may occur during the migration of immature worms through the liver and can develop months later when adult worms reach the bile ducts.
Long-term Clonorchis and Opisthorchis infection can cause chronic inflammation and damage to the bile ducts. Infections with C. sinensis and O. viverrini are associated with cancer of the bile duct, referred to as cholangiocarcinoma.
Diagnosis and treatment of Liver flukes
Diagnosis depends on the type of liver fluke and the timing and nature of the exposure. Stool testing can identify parasite eggs and may require more than one sample. Blood tests, ultrasound, CT or MRI may also be used depending on the suspected infection and clinical findings.
Tell your doctor if you have travelled to an area where liver flukes occur and have eaten raw or undercooked freshwater fish or freshwater plants. This travel and dietary history can help guide testing.
Treatment depends on the species with various antiparasitic medications available for the different types of liver flukes. Treatment should be prescribed by a doctor after the suspected infection has been assessed.
Prevention of Liver flukes
The most effective way for travellers to prevent liver fluke infection is to avoid raw or undercooked freshwater fish in areas where Clonorchis or Opisthorchis occur. Lightly salted, smoked or pickled freshwater fish may also contain infectious parasites.
Fasciola infection can be prevented by avoiding raw watercress and other freshwater plants in areas where the parasite occurs. Use safe drinking water and avoid consuming uncooked freshwater plants unless you are confident they have been safely prepared.
Australian Government travel advice recommends researching food and water risks before travelling and avoiding uncooked or undercooked food in destinations where foodborne infections are common. Discuss your itinerary and planned activities with a travel doctor before departure, particularly if you plan to eat local or traditional foods involving raw freshwater fish or plants.