Question
Giardia lamblia.
Answer
Giardia lamblia (G. intestinalis/G. duodenalis) is a flagellated protozoan parasite, one of the most common causes of parasitic diarrhoea worldwide, particularly affecting children and travellers.
Transmission: faecal-oral route, ingestion of the resistant cyst form in contaminated water (resistant to standard chlorination) or food, or direct person-to-person contact.
Morphology: the motile trophozoite is pear-shaped with two nuclei giving an “owl’s-eye” appearance, four pairs of flagella, and a ventral adhesive disc used to attach to (not invade) intestinal mucosa; the cyst is oval, thick-walled, containing four nuclei when mature.
Pathogenesis: trophozoites attach to but do not invade the small intestinal mucosa, causing malabsorption via mechanical coating of the brush border.
Clinical features: ranges from asymptomatic to acute/chronic diarrhoea — foul-smelling, greasy, non-bloody (steatorrhoeic) stools, abdominal cramps, bloating, and, in chronic infection, malabsorption/weight loss.
Laboratory diagnosis: stool microscopy for cysts (formed stool) and/or trophozoites (loose stool); stool antigen ELISA (more sensitive); string test (Entero-test) when stool exam is negative.
Treatment: metronidazole (or tinidazole).