Practice 7 structured short- and long-answer medical questions on Giardia lamblia and Intestinal Flagellates. Review model answers for exam revision.
Answer: ## Introduction Parasitic protozoa that use whip-like flagella for locomotion are known as flagellates. These belong to the phylum Sarcomastigophora, subphylum Mastigophora, and class Zoomastigophora. Flagellates are categorized based on their habitat: - **Lumen-dwelling flagellates**: Found in the alimentary and urogenital tracts (e.g., Giardia lamblia, Trichomonas vaginalis). - **Hemoflagellates**: Found in blood and tissues (e.g., Trypanosoma, Leishmania). ## Giardia lamblia ### History and Distribution Giardia lamblia is the most common protozoan pathogen worldwide, prevalent in areas with poor sanitation. It is a frequent cause of traveler’s diarrhea. ### Habitat It resides in the duodenum and upper jejunum. It is the only protozoan parasite found in the human small intestine. ### Morphology Giardia exists in two forms:
Answer: - Shape: Heart-shaped/pyriform (resembles a tennis racket). - Size: 15 µm × 9 µm. - Features: Bilaterally symmetrical, two nuclei, four pairs of flagella, and a ventral sucking disc for attachment. - Motility: Characteristic "falling leaf" motion.
Answer: - Shape: Oval/ellipsoid. - Size: 12 µm × 8 µm. - Features: Thick hyaline wall, four nuclei (in mature cysts), and internal remnants of flagella. ### Life Cycle - **Host**: Humans (Direct life cycle). - **Infective stage**: Mature cyst. - **Transmission**: Fecal-oral route via contaminated water or food. Infective dose is low (10–100 cysts). - **Excystation**: Occurs in the duodenum where one cyst releases two trophozoites. - **Encystation**: Occurs in the colon as feces dehydrate. ### Pathogenesis and Clinical Features - **Mechanism**: Trophozoites attach to the intestinal mucosa via sucking discs. They cause villous atrophy, apoptosis of epithelial cells, and loss of brush border enzymes (disaccharidase deficiency). - **Clinical Presentation**: - Often asymptomatic. - Acute/Chronic diarrhea: Mucus-rich, foul-smelling, but no blood. - Steatorrhea: Fatty stools due to malabsorption. - Abdominal cramps, flatulence, and epigastric pain. - In children: Malnutrition, weight loss, and growth retardation. ### Laboratory Diagnosis
Answer: Model answer pending
Answer: Model answer pending
Answer: Model answer pending
Answer: ### Treatment - **First-line**: Metronidazole (250 mg TID for 5–7 days) or Tinidazole (2g single dose). - **Children**: Nitazoxanide or Furazolidone. - **Pregnancy**: Paromomycin (non-absorbable aminoglycoside). ### Prevention - Boiling water (cysts are chlorine-resistant). - Filtration (1 µm pore size). - Proper hand hygiene and sewage disposal.