Giardiasis — DTM&H MCQ

Correct answer: A — Tinidazole or metronidazole

The correct answer is A, tinidazole or metronidazole. This traveller has classic giardiasis: chronic bloating and foul smelling, non bloody diarrhoea with weight loss following ingestion of untreated stream water, and normal eosinophils, which argues against a helminth cause. Giardia lamblia is a protozoan that colonises the small bowel and causes malabsorptive, fatty, offensive stools rather than invasive bloody diarrhoea, and it does not provoke a significant eosinophilia. Nitroimidazoles (tinidazole, or metronidazole where tinidazole is unavailable) are the first line agents, achieving high parasitological cure rates, with tinidazole favoured for its single dose convenience and comparable or superior efficacy to multi day metronidazole. Why the other options are wrong: E. Ivermectin: used for Strongyloides, scabies and some filarial infections; these typically cause peripheral eosinophilia, which is absent here, and ivermectin has no activity against Giardia. C. Fluconazole: an antifungal with no role in protozoal gut infection; there is no clinical picture here suggesting fungal disease. D. Ciprofloxacin: appropriate for bacterial dysentery or traveller's diarrhoea with blood or systemic sepsis, such as Shigella or Campylobacter, not for the non bloody, chronic, malodorous pattern typical of giardiasis, and Giardia is intrinsically resistant to fluoroquinolones. B. Praziquantel: treats trematodes and cestodes such as schistosomiasis or tapeworms, which usually cause eosinophilia and a different exposure history (freshwater bathing, not just drinking). Key point: Chronic foul smelling, non bloody diarrhoea with bloating after untreated water exposure, without eosinophilia, points to giardiasis, treated with tinidazole or metronidazole.

Reference: BNF, Metronidazole and Tinidazole, Indications: Giardiasis, National Institute for Health and Care Excellence / BNF, https://bnf.nice.org.uk/drugs/tinidazole/