What is the hallmark histological feature used to differentiate Schistosoma mansoni eggs found in stool?

• A. Terminal spine on the egg
• B. Lateral spine on the egg
• C. Double operculum
• D. No spine on the egg

Answer: (B)

The feature being tested is how the egg morphology of Schistosoma species distinguishes them under microscopy. Schistosoma mansoni eggs in stool are characterized by a prominent lateral spine on the side of the egg. This lateral spine is the key identifying mark that sets S. mansoni apart from other Schistosoma species, such as S. haematobium, which has a terminal (posterior) spine and is typically associated with urine samples. Some other flukes may have different features like opercula or no spines, so those patterns do not describe S. mansoni eggs found in stool. Thus, the lateral spine on the egg is the hallmark feature.