Unembryonated eggs with an inconspicuous operculum, a small knob on the end opposite the operculum, and a size around 65 to 75 μm were seen in the stool of a traveler who often eats raw fish. What is the most likely identification?

Unembryonated eggs with an inconspicuous operculum, a small knob on the end opposite the operculum, and a size around 65 to 75 μm were seen in the stool of a traveler who often eats raw fish. What is the most likely identification?

• A. Fasciola hepatica
• B. Diphyllobothrium latum
• C. Paragonimus westermani
• D. Clonorchis sinensis

Answer: (B)

Recognize a fish-tapeworm egg by its size, shape, and opercular features, along with the exposure history. The described eggs are unembryonated, about 65–75 μm long, oval, with an inconspicuous operculum and a small knob at the end opposite the operculum. This combination is classic for Diphyllobothrium latum, the fish tapeworm acquired from eating raw or undercooked freshwater fish. The size fits D. latum and the abopercular knob helps distinguish it from other trematode/cestode eggs. Larger eggs like Fasciola hepatica are not associated with raw fish consumption and are bigger; Paragonimus westermani eggs are typically linked to crustaceans and often found in sputum or stool with a different shell and prominence of the operculum; clonorchis sinensis eggs are much smaller. Therefore, the most likely identification is Diphyllobothrium latum.

Recognize a fish-tapeworm egg by its size, shape, and opercular features, along with the exposure history. The described eggs are unembryonated, about 65–75 μm long, oval, with an inconspicuous operculum and a small knob at the end opposite the operculum. This combination is classic for Diphyllobothrium latum, the fish tapeworm acquired from eating raw or undercooked freshwater fish. The size fits D. latum and the abopercular knob helps distinguish it from other trematode/cestode eggs. Larger eggs like Fasciola hepatica are not associated with raw fish consumption and are bigger; Paragonimus westermani eggs are typically linked to crustaceans and often found in sputum or stool with a different shell and prominence of the operculum; clonorchis sinensis eggs are much smaller. Therefore, the most likely identification is Diphyllobothrium latum.