Answer to Case 498

Answer: Taenia sp. eggs. I forgot to mention that the stool specimen came from a human patient. Therefore, the main considerations are Taenia solium and Taenia saginata. If the patient acquired infection in Asia, then Taenia asiatica should also be considered. You cannot differentiate the 3 species based on the egg alone, instead, morphologic features of the adult worm (T. saginata/T. asiatica vs. T. solium) and molecular testing (T. saginata vs. T. asiatica) are needed. The photographs and video beautifully highlight the key diagnostic features:

As a side note, the eggs of Echinococcus species have a very similar appearance but would be found in the stool of infected dogs and other canids, and NOT in human stool.

Thanks again to Heather in my lab for the beautiful photos and video!