Eggs measure 19-29 um long by 12-17 um wide. They have a knob at the abopercular end that may be prominent, inconspicuous, or absent.
Opisthorchiasis results from the liver flukes O. felineus and O. viverrini invading the biliary ducts of the human host as indicated in the diagram above.
First, a history of eating raw, pickled, or poorly cooked fish should be obtained.
Diagnosis is made on the detection of eggs in the patient's stool. Fewer than 100 eggs per gram of feces is considered evidence of mild infection and more than 30,000 eggs per gram is considered to indicate severe infection.
If eggs are not detected, examination of duodenal drainage aspiration may detect eggs. This procedure requires hospitalization and is usually indicative of severe infection as the flukes could be blocking ducts to such an extent that eggs cannot be passed on into the stool.
Indirect evidence of Opisthorchiasis in the bile ducts can be obtained by using radiologic techniques. Non-invasive ultrasonography has largely replaced the invasive procedure of obtaining duodenal drainage. Computed tomography can also be used to diagnose Opisthorchiasis.
The enzyme-linked immunosorbent assay (ELISA) remains the most appropriate immunodiagnostic technique for detecting Opisthorchiasis. Interestingly, one study found that the antibody titer to the Opisthorchis antigen was proportional to the changes in the liver detected through ultrasound. This makes ELISA a good predictor of the development of cholangiocarcinoma.