Liver Fluke

Liver fluke is an infection caused by parasitic flatworms (trematodes) that primarily affect your liver and bile ducts. These parasites are usually acquired by eating raw or undercooked fish, or contaminated aquatic plants. While some people have no symptoms, others may experience abdominal pain, fever, or jaundice, and chronic infection can lead to serious liver damage.

What is Liver Fluke?

Liver fluke is a parasitic infection caused by tiny flatworms, known as trematodes, that settle in your liver and the small tubes (bile ducts) that carry bile. These parasites can cause inflammation and damage, potentially leading to serious health problems if left untreated, though many people with mild infections may not experience any symptoms.

Liver flukes are a type of parasitic worm that can infect humans and animals. There are two main groups of liver flukes that commonly affect people: the sheep liver fluke (*Fasciola hepatica*) and the oriental liver flukes (*Clonorchis sinensis*, *Opisthorchis viverrini*, and *Opisthorchis felineus*). These parasites have complex life cycles involving snails as intermediate hosts. Humans become infected when they accidentally consume the larval stage of the fluke, which then travels to the liver. Once in the liver, the flukes mature and can live for many years, causing ongoing irritation and damage to the liver and bile ducts. The infection can range from mild, with no noticeable symptoms, to severe, leading to significant liver disease. The type of symptoms and their severity often depend on the number of flukes present and how long the infection has been active. Chronic infections, especially with oriental liver flukes, are linked to an increased risk of certain cancers.

Symptoms

Many people with a liver fluke infection, especially mild cases, may not experience any symptoms at all. When symptoms do occur, they can vary depending on the stage of the infection and the number of parasites, often including abdominal pain, fever, and digestive issues.

Symptoms of liver fluke infection can be divided into acute (early) and chronic (long-term) phases. In the acute phase, which occurs in the first few months after infection, you might experience general symptoms as the parasites migrate through your body. These can include fever, chills, skin rash, and an enlarged liver (hepatomegaly) that may be tender to the touch. As the infection progresses into the chronic phase, the flukes settle in the bile ducts. This can lead to more specific symptoms related to liver and digestive function. You might experience persistent abdominal pain, often in the upper right side of your abdomen, along with nausea, vomiting, and diarrhea. Some people also experience weight loss. More severe chronic symptoms can include jaundice (yellowing of the skin and eyes) due to blocked bile ducts, inflammation of the bile ducts (cholangitis), and the formation of gallstones. Over time, chronic inflammation can lead to significant liver damage and, in the case of oriental liver flukes, an increased risk of bile duct cancer (cholangiocarcinoma).

Causes & risk factors

Liver fluke infections are caused by consuming raw or undercooked freshwater fish or aquatic plants contaminated with the parasite larvae. The primary risk factors involve dietary habits and living in or traveling to regions where these parasites are common.

The cause of liver fluke infection is the ingestion of the larval stage of the parasite, called metacercariae. These larvae are typically found encysted on raw or undercooked freshwater fish, or on certain aquatic plants like watercress. The specific source depends on the type of liver fluke. For oriental liver flukes (*Clonorchis* and *Opisthorchis* species), the main cause of infection is eating raw or undercooked freshwater fish. The larvae are released from the fish in your digestive system and then travel to your bile ducts. For the sheep liver fluke (*Fasciola hepatica*), infection usually occurs from eating raw aquatic plants, such as watercress, that have been contaminated with the parasite larvae. Risk factors for liver fluke infection include living in or traveling to areas where these parasites are common (endemic areas), particularly in parts of Asia, Europe, South America, and Africa. Consuming traditional dishes that feature raw or undercooked freshwater fish, or eating raw aquatic vegetables from contaminated sources, significantly increases your risk. Poor sanitation and agricultural practices that allow parasite eggs to contaminate water sources also contribute to the spread of these infections.

How it's diagnosed

Diagnosing liver fluke infection typically involves identifying parasite eggs in your stool samples or detecting antibodies in your blood. Imaging tests may also be used to visualize the flukes or assess any damage they have caused to your liver and bile ducts.

Your doctor will usually start by asking about your symptoms, travel history, and dietary habits, especially if you have consumed raw fish or aquatic plants. The most common way to diagnose a liver fluke infection is by examining a stool sample under a microscope to look for the parasite's eggs. Multiple stool samples may be needed to increase the chance of finding eggs. Blood tests can also be helpful. A blood test may show an increased number of a type of white blood cell called eosinophils (eosinophilia), which often indicates a parasitic infection. Specific antibody tests can detect your body's immune response to the flukes, indicating exposure to the parasite. These tests are particularly useful in the early stages of infection before eggs are consistently shed in stool. In some cases, imaging tests may be performed to look for signs of flukes or damage to the liver and bile ducts. These can include ultrasound, computed tomography (CT) scans, or magnetic resonance imaging (MRI). A more specialized procedure called endoscopic retrograde cholangiopancreatography (ERCP) might be used to directly visualize the bile ducts, remove adult flukes, or relieve blockages caused by the infection.

Treatment options

Treatment for liver fluke infection involves specific anti-parasitic medications designed to kill the flukes. The choice of medication depends on the type of liver fluke causing the infection, and in some cases, surgery may be necessary to address complications.

The primary treatment for liver fluke infections is medication. The specific drug used depends on the type of liver fluke identified. For infections caused by oriental liver flukes (*Clonorchis sinensis* and *Opisthorchis* species), the medication of choice is praziquantel. This drug works by paralyzing the worms, allowing your body to clear them. For infections caused by the sheep liver fluke (*Fasciola hepatica*), the recommended treatment is triclabendazole. This medication is highly effective against *Fasciola* species. Your doctor will prescribe the appropriate medication and dosage based on your diagnosis and overall health. In cases where the infection has led to complications, such as severe bile duct blockage, gallstones, or significant liver damage, additional treatments may be necessary. This could include surgical procedures to remove blockages or gallstones, or to address other structural problems caused by the flukes. It is important to complete the full course of medication as prescribed by your doctor to ensure all parasites are eliminated.

Recovery & outlook

With appropriate and timely treatment, the outlook for most people with liver fluke infection is generally good, leading to full recovery. However, long-term complications, such as liver damage or bile duct cancer, can occur if the infection is chronic or left untreated.

For most people, especially those with mild or acute infections who receive prompt treatment, the recovery from liver fluke infection is usually complete. The anti-parasitic medications are generally effective at killing the flukes, and symptoms often resolve within a few weeks to months after treatment. Your doctor may recommend follow-up stool tests to confirm that the parasites have been successfully eliminated. However, the outlook can vary depending on several factors, including the type of fluke, the severity and duration of the infection, and whether any complications have developed. If the infection has been chronic and has caused significant damage to the liver or bile ducts, such as extensive scarring (fibrosis) or the formation of gallstones, these issues may require ongoing management or additional interventions. It is important to be aware that chronic infection with oriental liver flukes (*Clonorchis* and *Opisthorchis* species) is a known risk factor for developing bile duct cancer (cholangiocarcinoma). While successful treatment can eliminate the parasites, the risk of this cancer may persist, especially if the infection was long-standing. Regular medical follow-up may be advised for individuals with a history of chronic liver fluke infection to monitor for any long-term complications.

When to see a doctor

You should see a doctor if you suspect you have been exposed to liver flukes, especially if you have traveled to endemic areas or consumed raw fish or aquatic plants. Seek immediate medical attention if you develop severe abdominal pain, high fever, yellow skin or eyes (jaundice), or dark urine.

It is important to consult a doctor if you have any reason to believe you might have a liver fluke infection. This includes if you have recently traveled to regions where liver flukes are common and have eaten raw or undercooked freshwater fish or aquatic plants. Even if your symptoms are mild or non-existent, early diagnosis and treatment can prevent long-term complications. Seek medical attention promptly if you experience symptoms such as persistent abdominal pain, especially in the upper right side, unexplained fever, chills, or digestive issues like nausea, vomiting, or diarrhea. These symptoms could indicate an active infection that requires treatment. Additionally, certain symptoms warrant immediate medical evaluation as they can signal more serious complications. These include severe abdominal pain, a high fever, yellowing of your skin or the whites of your eyes (jaundice), dark urine, or light-colored stools. These signs could indicate significant bile duct blockage or liver inflammation, which require urgent medical care.

Frequently asked questions

How do liver flukes get into the body?

Liver flukes enter your body when you eat raw or undercooked freshwater fish, or raw aquatic plants like watercress, that contain the parasite's larval cysts (metacercariae). These larvae then travel from your digestive system to your liver and bile ducts.

Can liver fluke infection be prevented?

Yes, liver fluke infection can be prevented by thoroughly cooking all freshwater fish before eating it. You should also avoid eating raw aquatic plants, such as watercress, especially from areas where the parasite is common. Practicing good hygiene and ensuring proper sanitation can also help reduce risk.

Is liver fluke contagious from person to person?

No, liver fluke infection is not directly contagious from person to person. The parasite requires intermediate hosts, specifically snails and then fish or aquatic plants, to complete its life cycle and become infectious to humans. You cannot catch it from someone who is infected.

What is the difference between sheep liver fluke and oriental liver fluke?

The main difference lies in how they are acquired and the specific species of parasite. Sheep liver fluke (*Fasciola hepatica*) is typically acquired from contaminated aquatic plants, while oriental liver flukes (*Clonorchis sinensis*, *Opisthorchis viverrini*, *Opisthorchis felineus*) are usually acquired from raw or undercooked freshwater fish. They also respond to different medications for treatment.

How long can liver flukes live in a person?

Liver flukes can live for many years inside a person's body if the infection is left untreated. Some species can survive for decades, continuously causing inflammation and potential damage to the liver and bile ducts over time.

Can liver fluke cause cancer?

Yes, chronic infection with oriental liver flukes (*Clonorchis sinensis* and *Opisthorchis* species) is a known risk factor for developing bile duct cancer (cholangiocarcinoma). The long-term inflammation caused by these parasites can lead to changes in the cells that increase cancer risk.

Sources

• MedlinePlus — Liver Fluke
• Mayo Clinic — Liver Fluke
• Cochrane Library — Liver Fluke