Intestinal schistosomiasis — DTM&H MCQ

Correct answer: A — Praziquantel

C, Praziquantel, is correct because the vignette describes intestinal (hepatosplenic) schistosomiasis caused by Schistosoma mansoni, and praziquantel is the drug of choice for all Schistosoma species. The clinical picture (occupational freshwater exposure in an East African fisherman, bloody diarrhoea, hepatosplenomegaly, marked eosinophilia) together with the pathognomonic finding of ova with lateral spines on stool microscopy is diagnostic of S. mansoni. Praziquantel acts on the adult schistosome tegument, causing calcium influx, paralysis and death of the worm, and cures the infection with a short single-day course, making it the recommended first line agent by UK and WHO tropical medicine authorities. Why the other options are wrong: D. Ivermectin: this is used for strongyloidiasis, filarial disease and scabies, not for trematode (fluke) infections; it has no useful activity against Schistosoma species. B. Metronidazole: this treats protozoal infections such as amoebiasis and giardiasis, but has no activity against helminths, and would not address the eosinophilia or lateral spined ova seen here. E. Albendazole: this is effective against soil transmitted helminths (roundworm, hookworm, whipworm) and some tissue nematodes, but it is not effective against schistosomes. C. Chloroquine: this is an antimalarial with no anthelminthic action, and would be entirely inappropriate given the parasitological findings, which point away from malaria. Key point: lateral spined ova on stool microscopy identify Schistosoma mansoni, and praziquantel is the treatment of choice for all schistosome infections.

Reference: BNF (NICE), Praziquantel drug monograph, indications and dose in schistosomiasis, https://bnf.nice.org.uk/drug/praziquantel.html