Case #527 – November, 2020

56-year-old Korean immigrant sought medical attention for non-specific abdominal pain and mild, intermittent diarrhea. A stool specimen was collected and sent for ova and parasite (O & P) examination. Figures A and B show what was detected in low numbers on a wet-mount preparation following fecal concentration. The objects of interest average 30 micrometers in length. What is your diagnosis? Based on what criteria?

Figure A

Figure B

This was a case of clonorchiasis caused by Clonorchis sinensis or opisthorchiasis caused by Opisthorchis viverrini. Morphologic features shown included:

Oval shaped, embryonated operculate eggs within the size range for both C. sinensis and O. viverrini (C. sinensis 27-35 µm and 19-30 µm for O. viverrini).
Visible opercular “shoulders.”
Small abopercular knob.
Presence of a differentiated miracidium.

The eggs of C. sinensis, O. viverrini, and O. felineus are practically indistinguishable by morphology alone, which necessitates the examination of adult flukes or molecular techniques to accurately diagnose the cause of the infection. Geographically, C. sinensis is most common throughout Asia north of Thailand and the Philippines (including India). However, O. viverrini is the predominant liver fluke in Thailand, Laos, and Cambodia. The geographic location of this specimen suggests a likely diagnosis of C. sinensis rather than O. viverinni. Opisthorchis felineus can be excluded as it is found only in Northern Asia (Russia and Mongolia) and west into Central Europe. Eggs of minute intestinal flukes, especially Haplorchis spp., are also sometimes misidentified as Opisthorchiid eggs; definitive confirmation in some endemic areas requires recovery of adult flukes and/or genetic sequencing.