Schistosomiasis intermediate host — DTM&H MCQ

Correct answer: A — Biomphalaria snail

The correct answer is A, Biomphalaria snail. Biomphalaria species are the obligatory freshwater intermediate hosts for Schistosoma mansoni, in which miracidia develop into cercariae before infecting humans through skin contact with contaminated water. Schistosome species show strict snail host specificity, and this species snail relationship underpins targeted vector control (mollusciciding with niclosamide, habitat modification) in endemic programmes such as those in Tanzania. Recognising which snail genus corresponds to which schistosome species is essential for interpreting transmission foci and designing control interventions correctly. Why the other options are wrong: C. Bulinus snail: this genus transmits S. haematobium (and S. intercalatum/S. guineensis), the cause of urinary schistosomiasis, not S. mansoni. D. Thiara snail: this genus is associated with other trematode life cycles (such as certain paragonimiasis-related snails in some regions) and is not a recognised schistosome intermediate host. B. Oncomelania snail: this is the intermediate host for S. japonicum, found in East Asia, an entirely different geographic and epidemiological niche to S. mansoni in Tanzania. E. Lymnaea snail: this genus is the intermediate host for Fasciola hepatica (liver fluke), a distinct trematode with a different life cycle and definitive host range, not for any human Schistosoma species. Key point: Match the schistosome species to its unique snail genus, Biomphalaria for S. mansoni, Bulinus for S. haematobium, Oncomelania for S. japonicum, since control programmes are targeted by this species-specific snail vector.

Reference: NaTHNaC (National Travel Health Network and Centre), TravelHealthPro Schistosomiasis Factsheet: 'S. mansoni miracidia infect Biomphalaria snails, S. haematobium miracidia require Bulinus snails and S. japonicum prefers Oncomelania species.' https://travelhealthpro.org.uk/factsheet/28/schistosomiasis