Flukes are parasitic flatworms that infect various parts of the body (eg, blood vessels, gastrointestinal tract, lungs, liver) depending on the species.
Opisthorchiasis due to O. viverrini occurs mainly in northeast Thailand, Laos, and Cambodia; O. felineus occurs mainly in Europe and Asia, including the former Soviet Union.
The life cycle of Opisthorchis requires both snails and fish. Human disease resembles clonorchiasis and is acquired by eating raw or undercooked freshwater fish that contains infectious metacercariae (encysted stage). Dogs, cats, and other fish-eating mammals are also definitive hosts. After ingestion, metacercariae excyst and ascend through the ampulla of Vater into the biliary ducts, where they attach to the mucosa and mature. Adult flukes grow to 5 to 10 mm by 1 to 2 mm (O. viverrini) or 7 to 12 mm by 2 to 3 mm (O. felineus).
Most infections are subclinical. Symptoms of opisthorchiasis include vague gastrointestinal discomfort, diarrhea, and constipation. In chronic infection, symptoms may be more severe; hepatomegaly and undernutrition may be present. Rare complications include cholecystitis, cholangitis, and cholangiocarcinoma (bile duct cancer ). Vietnam veterans who develop cholangiocarcinoma may have been infected with O. viverrini or Clonorchis sinensis while they served in Southeast Asia (2).
Diagnosis of opisthorchiasis is by finding eggs in the feces. Ultrasonography, CT, MRI, cholangiography, or endoscopic retrograde cholangiopancreatography (ERCP) may show biliary tract abnormalities.
The treatment of choice for opisthorchiasis is one of the following:
Infection can be prevented by cooking freshwater fish.
1. 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.
2. 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.