Flukes are parasitic flatworms that infect various parts of the body (eg, blood vessels, gastrointestinal tract, lungs, liver) depending on the species.
Clonorchis is endemic in East Asia (China, South Korea, northern Vietnam, Taiwan, and parts of Russia), and infection occurs elsewhere among immigrants and people eating raw or undercooked fish, or sometimes shrimp, from endemic areas. The number of people infected with C. sinensis is growing, from an estimated 7 million in the 1990s to 15 million worldwide in the 2000s.
Pathophysiology of Clonorchiasis
Adult forms of C. sinensis live in the bile ducts. Eggs are passed in the stool and ingested by snails. Cercariae (free-swimming larvae) released from infected snails subsequently infect a variety of freshwater fish and shrimp. Humans become infected by eating raw, undercooked, dried, salted, or pickled fish, or less commonly freshwater shrimp, containing encysted metacercariae (resting or maturing stage). Metacercariae are released in the duodenum, enter the common bile duct through the ampulla of Vater, and migrate to smaller intrahepatic ducts (or occasionally the gallbladder and pancreatic ducts), where they mature into adults in about 1 month. The adults may live ≥ 25 years and grow to about 10 to 25 mm by 3 to 5 mm. Some U.S. Vietnam veterans have had serologic evidence of exposure to liver fluke infection when tested 5 decades after the war ended, but none had detectable liver fluke parasites by fecal examination ( 1 Symptoms and signs references Clonorchiasis is infection with the liver fluke Clonorchis sinensis. Infection is usually acquired by eating undercooked freshwater fish. Most infections are asymptomatic, but when present... read more ).
Symptoms and Signs of Clonorchiasis
Light trematode infections are usually asymptomatic; symptoms typically occur in patients with a greater worm burden and longer duration of infection. In the acute phase, heavier infections can cause fever, chills, epigastric pain, tender hepatomegaly, mild jaundice, and eosinophilia. Later, diarrhea may occur. Symptoms usually last for 2 to 4 weeks.
Chronic cholangitis in heavy infections may progress to atrophy of liver parenchyma and portal fibrosis Hepatic Fibrosis Hepatic fibrosis is overly exuberant wound healing in which excessive connective tissue builds up in the liver. The extracellular matrix is overproduced, degraded deficiently, or both. The trigger... read more . Jaundice may occur if a mass of flukes obstructs the biliary tree.
Other complications include suppurative cholangitis, cholelithiasis, pancreatitis, and, late in the course, cholangiocarcinoma Cholangiocarcinoma Primary liver cancer is usually hepatocellular carcinoma. The first manifestations of liver cancer are usually nonspecific, delaying the diagnosis. When diagnosed at advanced stages, prognosis... read more (bile duct cancer [ 2 Symptoms and signs references Clonorchiasis is infection with the liver fluke Clonorchis sinensis. Infection is usually acquired by eating undercooked freshwater fish. Most infections are asymptomatic, but when present... read more ]). Vietnam veterans who develop cholangiocarcinoma may have been infected with Clonorchis sinensis or Opisthorchis viverrini while they served in Southeast Asia ( 1 Symptoms and signs references Clonorchiasis is infection with the liver fluke Clonorchis sinensis. Infection is usually acquired by eating undercooked freshwater fish. Most infections are asymptomatic, but when present... read more ). The risk of cholangiocarcinoma is increased in parts of South East Asia and mortality is more common in men aged 40 to 65 years.
Symptoms and signs references
1. Psevdos G, Ford FM, Hong S-T: Screening US Vietnam veterans for liver fluke exposure 5 decades after the end of the war. Infectious Diseases in Clinical Practice 26(4):208–210, 2018. doi: 10.1097/IPC.0000000000000611
2. Xia J, Jiang SC, Peng HJ: Association between liver fluke infection and hepatobiliary pathological changes: A systematic review and meta-analysis. PLoS One 10 (7):e0132673, 2015. doi: 10.1371/journal.pone.0132673 eCollection 2015.
Diagnosis of Clonorchiasis
Microscopic examination of stool
Diagnosis of clonorchiasis is by finding eggs in the feces or duodenal contents. Eggs typically become detectable in the stool only 3 to 4 weeks after infection. The eggs are difficult to distinguish from those of Opisthorchis. Occasionally, the diagnosis is made by identifying adult flukes in surgical specimens or by doing percutaneous transhepatic cholangiography.
Other tests are nondiagnostic but may be abnormal; alkaline phosphatase and bilirubin may be elevated. High levels of circulating eosinophils and serum IgE are also common. Eosinophilia distinguishes liver fluke infection from acute viral hepatis Overview of Acute Viral Hepatitis Acute viral hepatitis is diffuse liver inflammation caused by specific hepatotropic viruses that have diverse modes of transmission and epidemiologies. A nonspecific viral prodrome is followed... read more .
A plain abdominal x-ray occasionally shows intrahepatic calcification. Hepatic ultrasonography, CT, MRI, endoscopic retrograde cholangiopancreatography (ERCP), or cholangiography may show ductal irregularities and evidence of scarring.
Ultrasound screening for periductal fibrosis in high risk patients (male, >50 years old) in endemic areas can improve early detection of cholangiocarcinoma and thus survival rate ( 1 Symptoms and signs references Clonorchiasis is infection with the liver fluke Clonorchis sinensis. Infection is usually acquired by eating undercooked freshwater fish. Most infections are asymptomatic, but when present... read more ).
1. Chamadol N, Khuntikeo N, Thinkhamrop B, et al: Association between periductal fibrosis and bile duct dilatation among a population at high risk of cholangiocarcinoma: a cross-sectional study of cholangiocarcinoma screening in Northeast Thailand. BMJ Open 9(3):e023217, 2019. doi: 10.1136/bmjopen-2018-023217 Erratum in: BMJ Open 9(5):e023217corr1, 2019. PMID: 30898798; PMCID: PMC6475358.
Treatment of Clonorchiasis
Praziquantel or albendazole
Treatment of clonorchiasis is with one of the following:
Praziquantel 25 mg/kg orally 3 times a day for 2 days
Albendazole 10 mg/kg orally once a day for 7 days
Biliary obstruction may require surgery.
Prevention involves thoroughly cooking freshwater fish and shrimp from endemic waters and not eating it raw, pickled, or wine-soaked. In endemic areas, mass treatment with praziquantel reduced clonorchiasis burden ( 1 Treatment reference Clonorchiasis is infection with the liver fluke Clonorchis sinensis. Infection is usually acquired by eating undercooked freshwater fish. Most infections are asymptomatic, but when present... read more ). Family members of infected people should be evaluated for infection with stool microscopy and blood count for eosinophilia.
1. Choi MH, Park SK, Li Z, et al: Effect of control strategies on prevalence, incidence and re-infection of clonorchiasis in endemic areas of China. PLoS Negl Trop Dis 4(2):e601, 2010. doi:10.1371/journal.pntd.0000601