Entamoeba histolytica and Amoebiasis | Essay Questions | Ompath Study

Practice 5 structured short- and long-answer medical questions on Entamoeba histolytica and Amoebiasis. Review model answers for exam revision.

Essay Questions and Answers

1. Q1. ### Introduction

   Answer: - *Entamoeba histolytica* is a protozoan parasite that causes amoebiasis, affecting the intestines and extraintestinal organs, primarily the liver. - It spreads through fecal-oral transmission via contaminated food and water. ### Life Cycle of Entamoeba histolytica

2. Q2. **Infective Stage**: The mature quadrinucleate cyst is the infective form. It is resistant to environmental conditions.

   Answer: Model answer pending

3. Q3. **Ingestion and Excystation**: When ingested, excystation occurs in the small intestine due to alkaline pH. Each cyst releases eight trophozoites, which migrate to the colon.

   Answer: Model answer pending

4. Q4. **Colonization and Multiplication**: Trophozoites attach to the colonic mucosa and multiply by binary fission. They may remain commensal in the lumen, invade the intestinal wall (causing ulcers), or spread to extraintestinal sites (liver, lungs, brain).

   Answer: Model answer pending

5. Q5. **Encystation and Exit**: Some trophozoites encyst in the colon. Mature quadrinucleate cysts are excreted in feces to infect new hosts.

   Answer: ### Pathogenesis of Amoebiasis #### 1. Intestinal Amoebiasis - Trophozoites invade the colonic epithelium, causing flask-shaped ulcers with undermined edges. - May lead to necrosis, hemorrhage, perforation, amoebic dysentery, fulminant colitis, toxic megacolon, and amoeboma. #### 2. Extraintestinal Amoebiasis - **Hepatic Amoebiasis (Amoebic Liver Abscess)**: Most common extraintestinal manifestation. Trophozoites reach the liver via the portal vein, causing "anchovy sauce-like" pus, hepatomegaly, and RUQ pain. - **Pulmonary Amoebiasis**: Occurs when a liver abscess ruptures through the diaphragm. Presents with pleuritic chest pain and chocolate-brown sputum. - **Cerebral Amoebiasis**: Rare but fatal hematogenous spread to the brain. - **Cutaneous and Genitourinary Amoebiasis**: Ulcerative lesions in the perianal or genital regions. ### Clinical Features #### Intestinal Amoebiasis - **Asymptomatic carriers**: 80-90% of cases. - **Amoebic colitis**: Gradual onset, mild abdominal pain, blood-stained mucus in stools, usually no fever. - **Fulminant Amoebic Colitis**: Severe pain, high fever, toxic symptoms; risk of toxic megacolon. #### Amoebic Liver Abscess - High-grade fever, chills, and RUQ pain. - Hepatomegaly and tender liver. - Aspirate contains anchovy sauce-like pus. ### Diagnosis #### Intestinal Amoebiasis - **Stool Microscopy**: Wet mount for cysts or trophozoites (with ingested RBCs). Trichrome stain for detail. - **Stool Culture**: NIH polygenic media, Craig’s, Nelson’s, or Robinson’s medium. - **Serology**: ELISA, PCR. - **Colonoscopy**: To visualize flask-shaped ulcers. #### Amoebic Liver Abscess - **Imaging**: Ultrasound, CT, or MRI showing hypoechoic abscess. - **Aspirate Microscopy**: Anchovy sauce pus; typically sterile (absence of bacteria). - **Serology**: Positive in 95% of cases. ### Treatment #### 1. Luminal Amoebicides (for intestinal colonization) - **Paromomycin**: 25-35 mg/kg/day in 3 doses for 7 days. - **Iodoquinol**: 650 mg 3 times/day for 20 days. - **Diloxanide furoate**: 500 mg 3 times/day for 10 days. #### 2. Tissue Amoebicides (for invasive/extraintestinal disease) - **Metronidazole**: 750 mg TID for 10 days (adults); 35-50 mg/kg/day for 10 days (children). - **Tinidazole**: 2 g/day for 3-5 days. - **Chloroquine**: Used for liver abscess if metronidazole fails (1 g/day for 2 days, then 500 mg/day for 3 weeks). #### 3. Combination Therapy - Systemic agent (Metronidazole/Tinidazole) plus a luminal agent (Paromomycin) to ensure complete eradication. ### Prevention and Control - **Personal Hygiene**: Handwashing and avoiding contaminated food/water. - **Water Purification**: Boiling, filtration, or chlorination. - **Public Health**: Proper disposal of human waste and treatment of asymptomatic carriers.