S. haematobium and bladder cancer — DTM&H MCQ

Correct answer: D — Schistosoma haematobium chronic infection

The correct answer is D, Schistosoma haematobium chronic infection. In Egypt and the wider Nile Delta, S. haematobium is endemic, and adult worm pairs reside in the vesical venous plexus, depositing eggs in the bladder wall that provoke chronic granulomatous inflammation, fibrosis and squamous metaplasia over decades. This sustained irritation and metaplastic change, compounded by endogenous nitrosamine formation from bacterial superinfection, is the recognised mechanism driving squamous cell carcinoma of the bladder, distinct from the transitional (urothelial) cell carcinoma seen with industrial or smoking-related bladder cancer in the UK. The freshwater swimming history in the Nile Delta is the classic exposure risk for cercarial penetration of skin, and IARC classifies chronic S. haematobium infection as a Group 1 carcinogen for bladder cancer. Why the other options are wrong: A. Schistosoma mansoni chronic infection: this species causes intestinal and hepatosplenic schistosomiasis via the mesenteric venous plexus, not urogenital disease, so it is not linked to bladder squamous cell carcinoma. B. Human papillomavirus infection: HPV is implicated in cervical, anogenital and some head and neck squamous cancers, but it is not an established cause of bladder squamous cell carcinoma, and there is no reference to sexual exposure in this stem. C. Opisthorchis viverrini chronic infection: this liver fluke, acquired from undercooked freshwater fish in Southeast Asia, causes cholangiocarcinoma, not bladder cancer, and is geographically and exposure-wise irrelevant here. E. Aristolochic acid exposure: this herbal nephrotoxin causes aristolochic acid nephropathy and upper urinary tract urothelial carcinoma, linked to Chinese herb nephropathy and Balkan endemic nephropathy, not freshwater exposure in Egypt. Key point: chronic S. haematobium infection from freshwater exposure in endemic areas like the Nile Delta causes bladder squamous cell carcinoma via egg-induced chronic inflammation and squamous metaplasia, unlike the urothelial carcinoma typical of Western risk factors.

Reference: NaTHNaC (National Travel Health Network and Centre), Schistosomiasis factsheet, travelhealthpro.org.uk, https://travelhealthpro.org.uk/factsheet/28/schistosomiasis