What is the common diagnostic feature for Diphyllobothrium latum in stool?

• A. Large, operculated eggs roughly 58–70 μm by 40–50 μm.
• B. Small, non-operculated eggs about 20 μm.
• C. Rhabditiform larvae in stool.
• D. Proglottids in stool.

Answer: (A)

The main concept here is that Diphyllobothrium latum is diagnosed most reliably by its distinctive eggs seen in stool. These eggs are large and have a lid-like opening called an operculum on one end, with a typical size around 58–70 μm long by 40–50 μm wide. That operculated, relatively large egg morphology is characteristic of this tapeworm and helps distinguish it from other intestinal parasites. While proglottids can be found for various tapeworms, and other organisms may produce different egg sizes or lack an operculum, the combination of large size and operculated eggs is the best diagnostic clue for Diphyllobothrium latum.