Biomphalaria snail — DTM&H MCQ
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Correct answer: B — Biomphalaria snail
The correct answer is B, Biomphalaria snail. Intestinal schistosomiasis with hepatosplenic involvement in Brazil is caused by Schistosoma mansoni, and Biomphalaria species are the only planorbid snails that act as intermediate hosts for this fluke. Miracidia released from human faeces infect Biomphalaria in freshwater streams, develop into cercariae, and these then re-infect humans percutaneously, closing the transmission cycle. The geography (Brazil), clinical picture (intestinal disease with hepatosplenomegaly from portal fibrosis) and snail family sampled (planorbid) all point specifically to S. mansoni and its Biomphalaria host, not to the urinary schistosome or other trematode hosts. Why the other options are wrong: D. Cyclops copepod: this crustacean is the intermediate host for Dracunculus medinensis (guinea worm) and some Diphyllobothrium species, not for any schistosome. E. Lymnaea snail: this is the intermediate host for Fasciola hepatica (liver fluke), a food borne trematode unrelated to schistosome transmission. C. Achatina snail: this large land snail transmits Angiostrongylus cantonensis (rat lungworm), causing eosinophilic meningitis, not schistosomiasis. A. Bulinus snail: this is the correct intermediate host for Schistosoma haematobium, which causes urinary tract disease (haematuria, bladder pathology), not intestinal or hepatosplenic disease. Key point: match the schistosome species to its snail host by clinical syndrome and geography, Biomphalaria for intestinal S. mansoni (hepatosplenic disease, the Americas and Africa) versus Bulinus for urinary S. haematobium.
Reference: NaTHNaC (travelhealthpro.org.uk), Schistosomiasis Factsheet, National Travel Health Network and Centre, UK: https://travelhealthpro.org.uk/factsheet/28/schistosomiasis