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 the Far East, especially in Korea, Japan, Taiwan, and southern China, and infection occurs elsewhere among immigrants and people eating raw or undercooked fish, or sometimes shrimp, from endemic areas.
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).
Light trematode infections are usually asymptomatic. In the acute phase, heavier infections can cause fever, chills, epigastric pain, tender hepatomegaly, mild jaundice, and eosinophilia. Later, diarrhea may occur.
Chronic cholangitis in heavy infections may progress to atrophy of liver parenchyma and portal fibrosis. 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 (bile duct cancer ). Vietnam veterans who develop cholangiocarcinoma may have been infected with C. sinensis or Opisthorchis viverrini while they served in Southeast Asia (1).
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 is by finding eggs in the feces or duodenal contents. 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, bilirubin, and eosinophil counts may be elevated.
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.
Treatment of clonorchiasis is with one of the following:
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.