Schistosomiasis treatment — DTM&H MCQ

Correct answer: B — Praziquantel

Praziquantel (option C) is correct because it is the drug of choice for treating established schistosomiasis, which is what this traveller has: positive serology with eosinophilia 10 weeks after freshwater exposure indicates that adult worms have matured and are producing the antigenic stimulus driving seroconversion, even though stool and urine microscopy remain negative (egg excretion is often intermittent or not yet established). Praziquantel acts on the adult fluke tegument, causing calcium influx, spastic paralysis and worm death, but it has little activity against immature schistosomulae, which is why treatment is timed to (or repeated after) 6 to 8 weeks post-exposure to allow worm maturation, a window that has clearly passed here. A single dose (or split doses) of praziquantel is therefore given even in seronegative-microscopy, seropositive, asymptomatic travellers with a compatible freshwater exposure history, as recommended in UK and international travel medicine practice. Why the other options are wrong: E. Diethylcarbamazine: this is used for filarial infections (e.g. loiasis, lymphatic filariasis) and has no activity against Schistosoma species. A. Albendazole: this is a benzimidazole active against soil-transmitted helminths and some tissue nematodes/cestodes, not against schistosome flukes. C. Ivermectin: this targets nematodes (e.g. strongyloidiasis, onchocerciasis) via glutamate-gated chloride channels, a mechanism irrelevant to trematodes like Schistosoma. D. Metronidazole: this treats protozoal and anaerobic bacterial infections (e.g. giardiasis, amoebiasis, bacterial vaginosis) and has no antischistosomal effect. Key point: treat presumptively with praziquantel once serology is positive and sufficient time (at least 6 to 8 weeks) has elapsed for worm maturation, even if microscopy for eggs is negative.

Reference: Joint Formulary Committee, British National Formulary (BNF): Praziquantel, indications and dose in schistosomiasis, https://bnf.nice.org.uk/drugs/praziquantel/