Introduction - Giardia lamblia (also called Giardia intestinalis or Giardia duodenalis ) is a protozoan parasite that causes giardiasis , an intestinal infecti
Introduction - Giardia lamblia (also called Giardia intestinalis or Giardia duodenalis ) is a protozoan parasite that causes giardiasis , an intestinal infection. - It is the only protozoan parasite found in the lumen of the small intestine (duodenum and upper jejunum). - Transmission occurs through ingestion of cysts in contaminated food and water or via direct person-to-person contact. Morphology of Giardia lamblia 1. Trophozoite (Vegetative Form) - Shape : Pear-shaped and bilaterally symmetrical. - Size : 9-21 µm long and 5-15 µm wide. - Motility : Resembles a falling leaf movement. - Key Features : Two nuclei with a central karyosome. - Four pairs of flagella (arising from a blepharoplast). - Axostyle (a supportive rod along the midline). - Ventral sucking disc (for attachment to the intestinal wall). - Two median bodies (sausage-shaped, located posterior to the sucking disc). 2. Cyst (Infective Form) - Shape : Oval or ellipsoid. - Size : 8-12 µm. - Key Features : Thick protective wall (resistant to environmental conditions). - Four nuclei (mature cyst). - Remnants of flagella and median bodies . - Infective Stage : Mature cysts are highly infectious and can survive in soil and water for weeks. Life Cycle of Giardia lamblia 1. Infective Stage - Mature cysts are ingested via contaminated water, food, or direct fecal-oral contact. 2. Excystation - Occurs in the small intestine within 30 minutes of ingestion. - Each cyst releases two trophozoites , which colonize the duodenum and jejunum . 3. Multiplication and Colonization - Trophozoites multiply by binary fission . - They attach to the intestinal mucosa using their ventral sucking disc , interfering with absorption but not invading tissue . 4. Encystation - Triggered by unfavorable conditions (dehydration, bile salts). - Encystment occurs in the colon , producing infective cysts that are excreted in feces. 5. Transmission - Cysts remain viable in the environment (water, soil, food) for weeks. - Infective dose: 10–100 cysts . . - Life Cycle of Giardia lamblia 1 Infective Stage → Mature cysts are ingested via contaminated food, water, or direct fecal-oral contact.2 Excystation → In the small intestine , each cyst releases two trophozoites within 30 minutes .3 Multiplication & Colonization → Trophozoites multiply by binary fission and attach to the duodenal and jejunal mucosa using their sucking disc .4 Encystation → Triggered by unfavorable conditions (dehydration, bile salts) in the colon , forming cysts.5 Excretion & Transmission → Cysts are excreted in feces and survive in soil, water, and food for weeks.6 Infection of New Host → Another person ingests cysts, continuing the cycle. Summary of Life Cycle Mature cyst ingested → Excystation in small intestine → Trophozoites multiply → Colonization of duodenum & jejunum → Encystation in colon → Cysts excreted in stool → Ingestion by a new host Pathogenesis and Clinical Features Pathogenesis - Does not invade tissue , but adheres tightly to the intestinal epithelium , causing: Villous atrophy (shortening of intestinal villi). - Apoptosis of enterocytes . - Malabsorption of fats and carbohydrates (steatorrhea). - Variant-Specific Surface Proteins (VSSP) allow Giardia to evade the immune system, leading to chronic infections . Clinical Features 1. Asymptomatic Carrier State - Majority (50-70%) of infected individuals show no symptoms . 2. Acute Giardiasis - Onset : 1-2 weeks after ingestion. - Symptoms : Watery diarrhea with excess mucus (no blood). - Foul-smelling stools , steatorrhea (fatty stools). - Dull epigastric pain, bloating, and flatulence . - Weight loss and malnutrition (due to fat, protein, and vitamin A malabsorption). - Lactose intolerance (temporary). 3. Chronic Giardiasis - Persistent diarrhea leading to malnutrition . - Vitamin A deficiency , weight loss, failure to thrive (in children). - Sprue-like syndrome (malabsorption syndrome). - Chronic fatigue . 4. Extraintestinal Manifestations - Biliary Giardiasis :Colonization of the gallbladder . - Causes biliary colic, jaundice, and cholecystitis . Diagnosis of Giardiasis 1. Stool Examination (Microscopy) - Wet mount : Detects trophozoites and cysts in fresh stool. - Concentration techniques (e.g., zinc sulfate flotation) improve detection. - Trichrome stain enhances visibility. 2. Entero-Test (String Test) - A gelatin capsule with a string is swallowed. - After 2 hours , it is retrieved and examined for trophozoites. - Not widely used due to high cost . 3. Serology and Molecular Tests - ELISA (Enzyme-Linked Immunosorbent Assay) – Detects Giardia antigens in stool. - PCR (Polymerase Chain Reaction) – Most sensitive test for diagnosis. 4. Duodenal Aspirate or Biopsy - Performed in chronic cases when stool tests are negative. - Detects trophozoites adhered to the intestinal mucosa . Treatment of Giardiasis 1. First-Line Drugs - Metronidazole : 250 mg, thrice daily for 5–7 days (adults). - 15 mg/kg/day in 3 doses for 5 days (children). - Cure rate: 90% . - Tinidazole : 2 g single dose (adults). - 50 mg/kg single dose (children). - More effective than metronidazole with fewer side effects. 2. Alternative Drugs - Furazolidone :100 mg QID for 7-10 days (preferred in children). - Nitazoxanide : 500 mg BID for 3 days (adults). - 200 mg BID for 3 days (children). - Paromomycin (safe in pregnancy): 25-35 mg/kg/day in 3 doses for 7 days . 3. Special Considerations - Pregnancy : Paromomycin preferred (avoids teratogenic effects of metronidazole). - Only symptomatic cases require treatment . Prevention and Control 1. Personal Hygiene - Handwashing with soap. - Proper disposal of diapers and human waste . 2. Safe Food and Water Practices - Avoid drinking untreated water from lakes, rivers, or wells. - Boiling water or using membrane filters (chlorination alone is ineffective). 3. Public Health Measures - Improved sanitation and sewage disposal . - Identification and treatment of carriers in outbreak situations. Summary Table ---