Amoebiasis is an intestinal infection caused by the protozoan Entamoeba histolytica, primarily affecting the colon's mucosal lining. It is a significant global health concern, especially in regions with poor sanitation and low socioeconomic status.
The infection ranges from asymptomatic cyst carriage to invasive disease causing dysentery and extra-intestinal complications such as liver abscess.
Epidemiology
- Worldwide distribution, endemic in tropical/subtropical areas with poor sanitation.
- Transmission mainly via fecal-oral route.
- Common in populations with low socioeconomic status and poor hygiene.
- Many infected individuals are asymptomatic cyst carriers.
- Approximately 10-20% of infected individuals develop invasive disease.
Etiology and Life Cycle of Entamoeba histolytica
- Exists in two forms:
- Trophozoite (vegetative form): Active, invasive form that multiplies in the intestinal mucosa.
- Cyst (infective form): Environmentally resistant, excreted in stool, infectious to new hosts.
- Cysts survive several days in moist environments such as water, soil, or contaminated food.
- Infection occurs after ingestion of mature cysts, which excyst in the small intestine to release trophozoites.
Transmission
- Fecal-oral route: Contaminated food, water, or direct person-to-person contact.
- Sexual transmission: Oral-anal contact, particularly among men who have sex with men.
- Mechanical vectors: Flies, cockroaches, rodents.
- Use of untreated human feces ("night soil") in agriculture facilitates spread.
- Incubation period ranges from days to weeks (typically 2-4 weeks).
Pathogenesis
- Trophozoites invade the colonic mucosa causing flask-shaped ulcers.
- Ulcers may perforate, leading to peritonitis.
- Invasive trophozoites can spread hematogenously, especially to the liver causing amoebic liver abscess.
- Can also rarely infect lungs, brain, and skin.
Clinical Presentation
| Clinical Form | Features |
|---|---|
| Asymptomatic Carrier | No symptoms, cysts present in stool |
| Amoebic Colitis / Dysentery | Abdominal pain, frequent small-volume bloody diarrhea, tenesmus, fever |
| Chronic Amoebiasis | Vague abdominal pain, diarrhea, fatigue, weight loss, intermittent fever |
| Amoebic Liver Abscess | Fever, right upper quadrant pain, hepatomegaly, malaise |
| Extra-intestinal Disease | Lung abscess, brain abscess, skin ulcers (rare) |
Diagnostic Investigations
- Microscopic stool examination: Identification of trophozoites (may contain ingested RBCs) and cysts.
- Stool antigen detection: Differentiates E. histolytica from nonpathogenic E. dispar.
- Serology (ELISA, IHA): Useful for liver abscess; antibodies may persist for years.
- Molecular methods (PCR): Gold standard for species differentiation.
- Imaging (Ultrasound, CT, MRI): Detect liver abscesses or cerebral involvement.
- Colonoscopy with biopsy: Identification of trophozoites in tissue samples.
- Laboratory tests: Elevated ESR, mild anemia, leukocytosis without eosinophilia; liver enzymes elevated in hepatic involvement.
Management
Asymptomatic Carriers
- Treatment only if the patient is a food handler or immunocompromised.
- Diloxanide furoate 500 mg orally twice daily for 10 days (luminal agent).
Intestinal Amoebiasis (Amoebic Dysentery)
- Metronidazole 500-750 mg orally three times daily for 7-10 days.
- Follow with a luminal agent (diloxanide furoate or paromomycin) to eradicate cysts.
Amoebic Liver Abscess
- Metronidazole 750 mg orally or IV once daily for 7-10 days.
- Percutaneous needle aspiration if:
- Abscess > 5-10 cm,
- Risk of rupture,
- Left lobe abscess,
- Failure to respond to medical treatment.
Complications
- Fulminant colitis with perforation and peritonitis.
- Rectovaginal fistula, toxic megacolon, and stricture formation.
- Rupture of liver abscess into peritoneal, pleural, or pericardial cavities.
- Disseminated infection: lung abscess, brain abscess.
- Secondary bacterial infections.
Prevention
- Improve sanitation and access to clean water.
- Proper disposal of human waste.
- Food hygiene and handwashing.
- Regular screening and treatment of food handlers.
- Avoid use of untreated night soil in agriculture.
Nursing Interventions
- Assessment
- Monitor vital signs, especially temperature and hydration status.
- Observe stool frequency, consistency, and presence of blood or mucus.
- Assess for abdominal tenderness, hepatomegaly, and signs of complications (peritonitis, jaundice).
- Hydration and Nutrition
- Maintain adequate hydration, administer IV fluids if necessary.
- Encourage small, frequent meals; avoid irritant foods.
- Medication Administration
- Administer prescribed anti-amoebic drugs with correct dosages and duration.
- Monitor for side effects of metronidazole (nausea, metallic taste, neurotoxicity).
- Educate patient on completing full course to prevent relapse.
- Infection Control
- Educate on hand hygiene, especially after defecation and before food handling.
- Use standard precautions to prevent spread.
- Patient Education
- Teach about disease transmission and prevention measures.
- Encourage safe sexual practices.
- Advise on the importance of clean water and food hygiene.
- Monitoring for Complications
- Observe for signs of worsening abdominal pain, persistent fever, or jaundice.
- Report immediately signs of liver abscess rupture or peritonitis.
- Psychosocial Support
- Provide reassurance about the prognosis.
- Support nutritional and social needs especially in chronic cases.
High-Yield Notes
- E. histolytica trophozoites ingest RBCs (pathognomonic).
- Flask-shaped ulcers in the colon are characteristic.
- Metronidazole kills trophozoites but not cysts; luminal agents eradicate cysts.
- Liver abscess commonly presents with "anchovy paste" pus on aspiration.
- Serology useful for invasive disease diagnosis, not for intestinal infection.
