What is Chinese Liver Fluke Infection?
Clonorchis sinensis, also known as the Chinese or Oriental liver fluke, is a type of parasitic worm commonly found in East Asia, including Korea, China, and Vietnam, and even in the far east regions of Russia. This parasite is typically found in mammals that eat fish, especially cats and dogs in areas where the parasite is widespread. However, humans can also get infected by eating contaminated fish.
Once inside a human host, Clonorchis sinensis can live for years in the bile ducts, the tubes that carry bile from the liver. Here, they can cause a range of health problems including inflammation of the gallbladder, infection of the bile ducts, and even bile duct cancer. This becomes a significant concern especially for Asian immigrants who have moved from regions where the parasite is common, as they can experience symptoms years after their initial infection.
This parasite poses a significant public health concern in some Asian regions, where over 200 million people are at risk of infection.
What Causes Chinese Liver Fluke Infection?
Clonorchiasis is usually caused by eating fish infected with C. sinensis. This tends to happen in certain parts of the world, particularly East Asia.
Here’s how the lifecycle of C. sinensis works:
The eggs of C. sinensis are released into water through feces. These eggs are then eaten by freshwater snails. Inside the snails, the eggs hatch into larvae that go through several stages of development. These larvae, called cercariae, then leave the snail and swim in the water until they find a freshwater fish. The larvae settle in the fish’s flesh, where they continue to grow into another stage called metacercariae.
When a person or another mammal eats the infected fish, the metacercariae inside the fish turn into juvenile flukes in the mammal’s small intestine. The flukes then grow into adults inside the bile ducts of the liver. It can take up to a month for them to fully grow. The whole cycle, from egg to adult, can take up to three months.
Various types of snails play a crucial role in this process as intermediate hosts. These snails are commonly found in local water bodies, including ponds, lakes, and rice fields. Eating raw or undercooked freshwater fish, particularly those from the Cyprinidae family, can lead to infection. Utensils and food contaminated with metacercariae can also potentially cause infection. This type of transmission is particularly common among children and women.
Risk Factors and Frequency for Chinese Liver Fluke Infection
C. sinensis is a disease largely found in Eastern parts of the world, including East Asia and parts of Russia. It used to be common in Japan as well but disappeared after World War II because of agricultural modernization changes. The risk of spreading this disease to other countries increases with travel or migration from areas where the disease is common.
Currently, it’s estimated that around 15 to 20 million people are infected with C. sinensis, with 13 million of these cases in China. This is a significant increase from the 1990s when only 7 million infections were estimated. As many as 200 million people could potentially be at risk of being infected with this disease because of the frequent consumption of undercooked fish. This is why the World Health Organization (WHO) classifies C. sinensis as one of the most neglected tropical diseases worldwide.
- Consumption of big fish, even when less contaminated, can lead to a build-up of the disease in the human bile ducts due to repeated exposure.
- Over 31 types of fish and shrimp, many of which are commonly consumed by humans, are known to carry C. sinensis.
A recent study found C. sinensis eggs in nearly 20% of stool samples from 500 school children aged 10 to 17 years in Hunan – one of the most highly affected areas of southeastern China. Other areas with high infection rates in China include the Guangdong province, near Hong Kong and Macau, and the Guangxi province.
While men often better understand the existence and risk of the disease, there are still misconceptions, like believing alcohol can prevent infection or that eating raw fish is healthy. In terms of infections, males are generally more affected than females, with infection rates rising with age, peaking in the 50s. Other ways of infection include contamination of food and cooking utensils, as cooked and uncooked food often isn’t separated. This is a common way the disease spreads among children and women.
Signs and Symptoms of Chinese Liver Fluke Infection
Infection with liver flukes, a type of worm, can cause various symptoms based on how many worms are present and how long the infection lasts. The more worms and the longer the infection, the more symptoms a person might have. After eating infected fish, symptoms may appear within 10 to 30 days and last for 2 to 4 weeks. People with a lot of worms may have long-term symptoms due to damage to their bile ducts.
Initially, a person with few worms is likely to have no symptoms. But, individuals with a large number of parasites might experience symptoms like yellowing of the skin, pain in the upper right portion of the stomach, nausea, vomiting, loss of appetite, tiredness, and fever. Besides, chronic infection with liver flukes can cause symptoms related to the liver and bile ducts. The presence of gallstones is common and is likely influenced by the parasite.
- Yellowing of the skin
- Upper right stomach pain
- Nausea
- Vomiting
- Loss of appetite
- Tiredness
- Fever
- Gallstones
The parasite has been associated with changes in the gallbladder wall that result in fewer contractions and subsequent build-up of certain chemicals on the parasitic eggs. Moreover, certain conditions like pancreatitis and liver abscesses are seen frequently in individuals with this infestation. Continuous obstruction and tightening of the bile ducts can lead to bile buildup and recurring infections. Liver cancer is another complication of long-term inflammation. In children, a high number of parasites can potentially lead to delayed development due to continuous diarrhea, lack of proper nutrition, and anemia.
Testing for Chinese Liver Fluke Infection
Doctors often diagnose C. sinensis – a small liver fluke parasite – by looking for its eggs in a patient’s stool. Finding these eggs can also give an idea about how serious the infection is. However, it’s noteworthy that absence of these eggs in feces does not confirm absence of infection; especially in cases where the bile ducts are blocked. In such scenarios, doctors can directly detect these parasites in fluids aspirated from the small intestine (duodenal) or bile secretions collected during a procedure called endoscopic retrograde cholangiopancreatography (ERCP).
There are other diagnostic methods as well. A direct fecal smear test using a technique called Kato-Katz method can show the eggs, whose visibility depends on the severity of infection. Sometimes, however, it’s difficult to tell the eggs of Clonorchis sinensis apart from another similar-looking parasite called Opisthorchis viverrine – that’s when doctors consider the patient’s geographical exposure to these parasites.
There’s another reliable method – the formalin-ether centrifuge sedimentation – which can concentrate these eggs in the feces in a way that’s more efficient than the Kato-Katz method, particularly in low-intensity cases. Blood tests like enzyme-linked immunosorbent assay (ELISA) are common and useful in diagnosing C. sinensis. Polymerase chain reaction (PCR) tests are another strong diagnostic tool, but might not be always available.
Doctors also use imaging techniques such as ultrasound, CT scans, and MRIs to track the location, advancement, and extent of the infection. While generally useful, these tools do have some limitations. For example, ultrasound can pick up signs of infection like widened bile ducts in the liver, but this by itself is not enough for a diagnosis and also depends significantly on the skill of the operator. However, CT scans can provide more detailed images to help doctors determine a diagnosis, especially by comparing larger unaffected bile ducts to the smaller ones that are typically affected. MRI imaging provides additional help in detecting C. sinensis; one classic sign on an MRI is the appearance of “too many intrahepatic ducts”, which suggests blockage of these smaller bile ducts due to the parasite.
Please note that despite recent technological advances, diagnosis of C. sinensis can often be challenging due to lack of tools and training in the impacted areas.
Treatment Options for Chinese Liver Fluke Infection
Praziquantel is the most effective treatment for clonorchiasis, a type of parasitic infection. The World Health Organization recommends doses of 25 mg/kg taken orally three times a day for 2 to 3 days, or a single dose of 40mg/kg. This treatment has a success rate of over 90%. Depending on the region, the recommended dosage may vary. In some places, larger doses, like 75 mg/kg of Praziquantel, are given twice within 48 hours. If the infection is severe or eggs are still found in the feces after initial treatment, another round of medication is necessary. Side effects of Praziquantel can include abdominal discomfort, vomiting, and headaches.
It’s important to remember that even with successful treatment, the bile duct’s recovery might take weeks and symptoms can persist. This fact, combined with the common issue that many people unknowingly host the parasite because symptoms are vague, led to studies in heavily-infected areas involving mass treatments with Praziquantel. These studies showed promising results, including a significant drop in infection rates from 59.5% in 2001 to 7.5% in 2004.
An alternative treatment involves albendazole, taken at 10mg/kg for 5 to 7 days. Because it’s common for the infection to spread within households or close contact groups due to shared food or contact with infected surfaces, family members and close contacts should also be tested.
Recent research also suggests tribendimidine, a new drug with a promising cure rate and side effect profile, as another treatment option. There’s also ongoing work to develop a vaccine, although it has only been tested in animals so far.
What else can Chinese Liver Fluke Infection be?
When ruling out other potential health issues before making a diagnosis, doctors often consider several other conditions that have similar symptoms. In this case, they could be considering:
- Acute hepatitis, which is a severe, sudden inflammation of the liver
- Cholecystitis, or inflammation of the gallbladder
- Choledocholithiasis, or stones in the bile duct
- Cholangiocarcinoma, a type of liver cancer that affects the bile ducts
- Primary sclerosing cholangitis, a disease that damages the bile ducts
- Primary biliary cholangitis, a disease that slowly destroys the liver’s bile ducts
- Other parasitic infections, such as schistosomiasis, fascioliasis, and ascariasis, which affect various organs and can cause a wide range of symptoms.
Doctors use detailed tests to evaluate these various possibilities and to arrive at the most accurate diagnosis.
What to expect with Chinese Liver Fluke Infection
One way of predicting the severity of an infection is by counting the number of eggs found in the feces. The more eggs found, the more severe the infection is likely to be. Many people don’t initially realize they’re infected, as they either don’t show any symptoms or the symptoms they do show are fairly vague.
The sooner the treatment for the infection starts, the better. If the treatment is delayed, it can take up to 12 weeks for the damage to the bile duct to heal, and if the infection is severe or lasts a long time, some of this damage might be permanent.
The symptoms of this infection can be easy to miss which can lead to the worms infecting for many years unnoticed. If complications such as inflammation of the gallbladder or bile duct, or liver abscesses occur, treating the symptoms usually helps. A type of bile duct cancer, called cholangiocarcinoma, has a poor prognosis though, with most people surviving less than 30 months.
Possible Complications When Diagnosed with Chinese Liver Fluke Infection
In 2009, the international agency for cancer research identified C. sinensis, a type of parasite, as a cause of cancer. The parasites live in the bile ducts of the liver. They can lead to blockages, inflammation, and scarring, potentially leading to a type of cancer called cholangiocarcinoma (CCA). One study even suggested that C. sinensis could contribute to liver cancer. This risk increases if the patient also has hepatitis B (HBV) and/or struggles with alcohol. Because the early symptoms are often subtle and overlooked for years, harmful changes in the body, such as the growth and scarring of bile ducts, can lead to dangerous growths without being detected.
A long-lasting infection also raises the risk of narrowing bile ducts. Along with blockages caused by the parasite, this can lead to repeated infections of the bile ducts, inflammation of the pancreas, and abscesses in the liver. If a person is infected with C. sinensis, they are at a higher risk for both intrahepatic (within the liver) and extrahepatic (outside the liver) CCA. Additionally, children with a high number of parasites might face developmental problems due to consistent diarrhea, malnourishment, and anemia.
Common Risks:
- Cholangiocarcinoma (CCA)
- Liver cancer, especially in combination with HBV and/or alcohol use
- Narrowing of the bile ducts
- Repeated bile duct infections
- Inflammation of the pancreas
- Liver abscesses
- Intrahepatic and extrahepatic CCA
- Developmental problems in children due to diarrhea, malnourishment, and anemia
Preventing Chinese Liver Fluke Infection
To prevent the spread of C. sinensis infection, it’s crucial to focus on educating people and ensuring food is prepared correctly. This is particularly important in areas where the infection is common. Public awareness campaigns, health guide booklets, and education in schools are some of the ways in which people are taught about the importance of properly preparing food and avoiding the consumption of undercooked or raw fish. It’s also important to separate farm animals from nearby fish farms and to know the symptoms of the infection. Significant cultural changes, such as moving farm animals away from water sources and reducing the consumption of raw fish, need to be made. Implementing these changes can help lower the infection rates of C. sinensis.