Question
Giardiasis
Answer
Giardiasis is caused by Giardia lamblia, a flagellated protozoan, one of the most common causes of parasitic diarrhoea worldwide, particularly in children and travellers.
Transmission: faecal-oral route, via ingestion of the resistant cyst form in contaminated water (resistant to standard chlorination) or food.
Life cycle: ingested cysts excyst in the duodenum, releasing the motile, flagellated, pear-shaped trophozoite (two nuclei, “owl’s-eye” appearance, ventral adhesive disc), which attaches to but does not invade the intestinal mucosa, impairing absorption; some trophozoites re-encyst and are excreted in stool.
Clinical features: asymptomatic carriage to acute/chronic diarrhoea — foul-smelling, greasy, non-bloody (steatorrhoeic) stools, abdominal cramps, bloating, and, in chronic cases, 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 but suspicion remains.
Treatment: metronidazole (or tinidazole).