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.
Transmission: faecal-oral route, ingestion of the resistant cyst form in contaminated water (resistant to standard chlorination) or food.
Morphology: the trophozoite is pear-shaped with two nuclei (“owl’s-eye” appearance), four pairs of flagella, and a ventral adhesive disc; 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: asymptomatic carriage to acute/chronic diarrhoea — foul-smelling, greasy, non-bloody stools, abdominal cramps, bloating, and, in chronic infection, malabsorption/weight loss.
Laboratory diagnosis: stool microscopy for cysts/trophozoites; stool antigen ELISA (more sensitive); string test (Entero-test) when stool exam is negative.
Treatment: metronidazole (or tinidazole).