Digestive Health
Diseases & Conditions
Contributed byMaulik P. Purohit MD MPHNov 15, 2019

What are the other Names for this Condition? (Also known as/Synonyms)

  • Chinese Liver Fluke Disease
  • Clonorchis Sinensis Infection
  • Oriental Liver Fluke Disease

What is Clonorchiasis? (Definition/Background Information)

  • Clonorchiasis is an infection caused by a parasitic worm, the Chinese liver fluke, or scientifically called Clonorchis sinensis (also known as Opisthorchis sinensis). The term “fluke” means flatfish, since these parasites are flat
  • The parasite has various stages (life cycle), before it develops into a fully-grown worm
    • At the very early stage, it moves from water (environment) into the body of a mollusk, such as a snail. Following this, it leaves the mollusk body and enters into a freshwater fish, such as a smelt
    • Humans ingest the parasite when they eat the raw, partially-cooked, salted, or under-processed fish. More commonly, dogs, cats, pigs, and rats eat the freshwater fish and easily ingest the parasite
    • Once in the body of humans, it resides and grows into an adult worm, measuring up to 1.5 cm in size in the liver bile ducts
    • The adult worm lays and hatches its eggs, which gets passed into the intestine from the bile duct and come out through stool, into the environment. In this manner, the life-cycle of the parasite continues
    • The parasitic worm can live in the bile duct or the liver for 20-30 years     
  • Clonorchiasis, or the Chinese Liver Fluke Disease, is common in China, Vietnam, Korea, East Asia, Japan, and Russia, due to the practice of eating raw, freshwater fish
  • In humans, the acute infectious stage is usually asymptomatic. In chronic infections, bile duct and liver abnormalities, such as abdominal pain (especially on the right side near the rib cage), are common. It may also cause inflammation of the liver
  • If chronic infection is left untreated, it may lead to bile duct cancer (cholangiocarcinoma)

Who gets Clonorchiasis? (Age and Sex Distribution)

  • Any individual consuming raw, uncooked, or unprocessed freshwater fish in the endemic regions, where the parasite is prevalent, is at risk for Clonorchiasis. Individuals of any race or ethnicity may be affected
  • People, who consume imported, undercooked, or pickled freshwater fish, containing the parasitic cysts of Clonorchis sinensis, are likely to be infected with Clonorchiasis
  • The condition, though, commonly affects males over 40 years of age, mainly because raw fish consumption along with chronic alcohol intake and smoking are more typically seen among this group. Very rarely do children get infected with Clonorchiasis
  • The Chinese Liver Fluke Disease is generally observed in people of certain Asian countries such as Korea, China, Taiwan, Vietnam, Japan, and eastern Russia. In non-endemic areas such as the US, it is more common among Asian immigrants

What are the Risk Factors for Clonorchiasis? (Predisposing Factors)

The risk factors of Clonorchiasis include:

  • People who eat freshwater fish that is raw, undercooked, pickled, or unprocessed (even if imported), containing the parasitic worms are at a high risk of contracting Clonorchiasis
  • Living near freshwater water bodies, such as rivers, ponds, or lakes, in the endemic regions of Korea, China, Taiwan, Vietnam, or Japan, where these parasites are highly prevalent and consuming raw fish

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases ones chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Clonorchiasis? (Etiology)

  • Clonorchiasis is a foodborne infection caused by Clonorchis sinensis or Chinese liver fluke, a parasitic worm which grows and resides in the bile ducts of the liver in humans and fish-eating mammals. It is acquired by eating freshwater fish containing the fluke larvae
  • The eggs of Clonorchis sinensis are taken in by snails that live in the freshwaters. These eggs hatch and the infected snails release microscopic larvae that enter freshwater fish (a carp-like fish that serves as an intermediate host). Humans (or mammals), who are the final hosts, are infected when they eat raw or undercooked fish containing the cysts
  • On entering the human body, the cyst travels to the intestine and then moves to the liver and resides in the bile ducts, where they grow into adult worms. The adult worm lays and hatches eggs that is passed on to the intestine and then into the feces

What are the Signs and Symptoms of Clonorchiasis?

Most individuals infected with Clonorchiasis do not present any symptoms. Individuals infected for a long time (chronic) may get serious illness. A long-standing inflammation or re-infection of the bile ducts could lead to scarring of the bile duct, and inflammation of the liver.

The signs and symptoms of Clonorchiasis may include:

  • Abdominal pain, nausea, and diarrhea
  • Any pathology (infection) of the bile duct and adjacent organs can cause abdominal pain (particularly under the rib cage to the right), jaundice, fever, or chills
  • Biliary stone formation (cholelithiasis): Inflammation and scarring of the bile ducts leads to stasis (decreased flow) of bile, which may to lead to the formation of stones
  • Due to bile stones and narrowing changes, the affected individuals may get the following:
    • Jaundice
    • Intermittent biliary duct obstruction can cause abdominal pain (biliary colic)
    • Cholangitis - infection and inflammation of the bile duct
    • Cholecystitis - infection and inflammation of the gall bladder        
  • Pancreatitis (inflammation of the pancreas) due to obstruction of the tube (duct) that is common to the liver bile duct and pancreas

How is Clonorchiasis Diagnosed?

The following tests and procedures may be used to diagnose Clonorchiasis:

  • Thorough evaluation of the individual’s medical history and a complete physical examination, especially of the abdomen
  • During history taking the physician may want to know the following:
    • When the symptoms began and whether they are becoming worse
    • Information on dietary habits (especially raw fish consumption), travel history, and places of residence       
  • The diagnosis of Clonorchiasis or opisthorchiasis (a similar condition) is suspected when the individual is accustomed to consuming raw fish and has signs and symptoms pertaining to the right side of the abdomen
  • Consultation with a gastroenterologist and or infectious disease specialist may be necessary
  • Blood tests:
    • Complete blood count may show eosinophilia - increased levels of white blood cell eosinophils in the peripheral blood. It is usually seen with parasitic infections
    • Tests for checking antibody levels for the parasite
  • Examination of a stool sample may be undertaken to detect the presence of the eggs of Clonorchis sinensis to confirm diagnosis
  • Imaging tests may be performed to look for disease activity in the bile duct, liver, gallbladder, or pancreatic duct
    • Ultrasound, CT, or MRI scans of the liver, gallbladder, biliary and pancreatic ducts may be taken
    • Endoscopic retrograde cholangiopancreatography (ERCP) may be done to check for abnormalities in the biliary and pancreatic ducts             

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Clonorchiasis?

The complications of Clonorchiasis could include:

  • Scarring of the bile duct or gallstone formation that could lead to diseases such as
    • Cholecystitis (infection of the gallbladder)
    • Cholangitis (infection of the biliary duct)             
  • Hepatitis (inflammation of the liver)
  • Cholangiocarcinoma - cancerous growth in one of the duct that carries bile from the liver to the small intestines

How is Clonorchiasis Treated?

The treatment options of Clonorchiasis include:

  • The World Health Organization (WHO) recommends anti-worm medication praziquantel for infected individuals. Praziquantel may be given to individuals as a preventative measure; to individuals who have no signs of the disease, but live in the endemic regions
  • Surgery may be required, if obstruction of the bile duct persists, despite treatment with praziquantel to remove the worms and/or stones
  • Treatment of complications as required with intravenous antibiotics and through surgical intervention

How can Clonorchiasis be Prevented?

The preventative measures of Clonorchiasis include:

  • Educating the community is the most important and effective tool in preventing Clonorchiasis
  •  Avoidance of raw or undercooked freshwater fish consumption. However, it has been observed that some individuals do not stop the habit, despite understanding the consequences
  • Clonorchiasis can be prevented by freezing fish (Centers for Disease Control and Prevention recommendation) using one of the strategies:
    • At -4⁰F or below for 7 days
    • At -31⁰F or below until solid and then storing at -31⁰F or below for 15 hours
    • At -31⁰F or below until solid and then storing at -4⁰F or below for 24 hours           
  • Cooking fish adequately to an internal temperature of at least 145⁰ F
  • Reducing the use of night soil, a fertilizer contaminated with human feces, which is used in some places to fertilize fish ponds to increase fish production. This practice must be strictly eliminated to prevent Clonorchiasis

What is the Prognosis of Clonorchiasis? (Outcomes/Resolutions)

A proper and timely diagnosis and treatment can lead to a good prognosis. Early diagnosis may prevent long-term complications of Clonorchiasis such as cholangiocarcinoma.

Additional and Relevant Useful Information for Clonorchiasis:

  • Clonorchiasis has been reported in the US among some immigrant population. Suspicion for Clonorchiasis should be high in immigrants from Asia, who present with bile duct disorders
  • Opisthorchiasis is another disease, in which the parasite has a similar life-cycle and clinical presentation. Opisthorchiasis infection is common in Russia and Eastern Europe
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Maulik P. Purohit MD MPH picture
Approved by

Maulik P. Purohit MD MPH

Assistant Medical Director, Medical Editorial Board, DoveMed Team


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