Which parasite produces eggs characterized by a large lateral projection?

• A. Schistosoma haematobium
• B. Fasciolopsis buski
• C. Schistosoma mansoni
• D. Paragonimus westermani

Answer: (C)

Egg morphology of schistosomes is a key identifying feature, and the position of the spine on the egg helps differentiate species. A large spine located on the side of the egg—the lateral spine—is characteristic of Schistosoma mansoni. This prominent lateral spine sets it apart from other schistosomes, such as Schistosoma haematobium, which has a terminal (tip) spine, and Schistosoma japonicum, which has a small, less conspicuous spine. Other trematode eggs, like those of Fasciolopsis buski and Paragonimus westermani, typically show an operculum rather than a lateral spine. Thus, the presence of a large lateral spine on the egg points to Schistosoma mansoni.