INTESTINAL – GIARDIA LAMBLIA

Giardia lamblia – intestinal protozoan

1. Definition – flagellated protozoan causing giardiasis, a non‑invasive infection of the upper small intestine.

2. Cause / transmission – ingestion of mature cysts in contaminated water, food, or by fecal‑oral contact (hand‑mouth, animal‑to‑human).

3. Types – two morphological forms: trophozoite (active) and cyst (infective).

4. Morphology –
   • Trophozoite: 10–20 µm × 5–15 µm, pear‑shaped, 8 flagella, ventral sucking disc, two nuclei, axonemes, median body.
   • Cyst: 9–12 µm × 5–9 µm, oval, thick chitinous wall, contains 2–4 trophozoites, resistant to gastric acid.

5. Life cycle (step‑wise) –

   1. Cyst → ingested with water/food.
   2. Cyst → passes stomach, wall protects against HCl.
   3. Cyst → excysts in duodenum, releases 2 trophozoites.
   4. Trophozoite → attaches to duodenal/jejunal brush border via ventral disc.
   5. Trophozoite → multiplies by binary fission (local infection).
   6. Trophozoite → encysts in distal ileum → forms new cysts.
   7. Cyst → expelled in feces → contaminates environment → next host.

   Memory trick – “C‑I‑E‑A‑M‑E‑C”: Contaminated Ingestion → Excyst → Attach → Multiply → Encyst → Contaminate.

6. Pathogenesis (step‑wise) –
   • Ingestion → cysts reach duodenum → excystation.
   • Trophozoites attach → ventral disc → mechanical disruption of microvilli.
   • Attachment → local brush‑border enzyme loss → malabsorption of fats & carbs.
   • Parasite metabolism → production of toxic metabolites (e.g., cysteine proteases) → epithelial cell apoptosis.
   • Result → increased intestinal permeability → watery, greasy stools and inflammation.

   Arrow flow: cyst → excyst → attach → damage → malabsorption → diarrhea.

7. Clinical features –
   • Loose, foul‑smelling, greasy stools (steatorrhea).
   • Abdominal cramps, bloating, flatulence.
   • Nausea, occasional vomiting.
   • Weight loss, failure to thrive (children).
   • Fatigue, mild fever (occasionally).

8. Complications –
   • Chronic malabsorption → nutritional deficiencies (vitamin A, iron).
   • Dehydration, electrolyte imbalance.
   • Post‑infectious irritable bowel syndrome.
   • Increased susceptibility to other enteric infections.

9. Diagnosis –
   • Stool microscopy: 3‑day stool exam for cysts/trophozoites (wet mount, iodine stain).
   • Antigen detection ELISA/ICT – higher sensitivity.
   • Duodenal aspirate or string test (Enterotest) for trophozoites.
   • PCR – confirmatory, especially in low‑parasite load.

10. Management –
    • Metronidazole 250 mg TID × 5‑7 days (first line).
    • Tinidazole 2 g single dose or 500 mg BID × 3 days (alternative).
    • Nitazoxanide 500 mg BID × 3 days (for children or resistant cases).
    • Re‑hydration therapy + oral rehydration salts.
    • Nutritional support: high‑calorie, low‑fat diet, supplementation of vitamins/minerals.

11. Prevention –
    • Drink boiled or filtered water; avoid untreated surface water.
    • Wash fruits/vegetables thoroughly.
    • Practice hand hygiene after toilet and before meals.
    • Proper sanitation of animal pens; avoid fecal contamination of water sources.

12. Memory rhyme for clinical picture – “Greasy stools, cramps, and loss, Giardia’s the boss!”