Case Study 2 - Diagnosis: Amoebic Liver Abscess (Hepatic Amoebiasis)

1. Diagnosis

• Imaging: Ultrasound or CT scan - shows single (80%) or multiple hypoechoic lesions, predominantly in the right lobe. In this case, CT confirmed multiple liver abscesses.
• Serology: Indirect haemagglutination (IHA) and ELISA are highly sensitive (>90%) for extraintestinal amoebiasis. Serology is often negative in purely intestinal disease.
• PCR of abscess material: As in this case, PCR is the most sensitive method when cultures are negative and serology inconclusive - it confirmed the diagnosis here.
• Stool antigen detection: ELISA-based antigen kits are specific for E. histolytica (not the non-pathogenic E. dispar). Post-treatment stool antigen and PCR were negative, confirming eradication.
• Aspiration: Yields the classic "anchovy sauce" (chocolate-brown, odourless) fluid - a mixture of necrotic liver and blood. Trophozoites are found in the abscess wall (not the pus) in only a minority of cases.
• Blood cultures: Negative (as in this patient) - distinguishing ALA from pyogenic liver abscess.
• Yamada's Textbook of Gastroenterology, 7th ed.
• Bailey and Love's Short Practice of Surgery, 28th ed.

2. Life Cycle of Entamoeba histolytica

Trichrome-stained stool sample containing an E. histolytica mature cyst with oblong chromatin bodies and four nuclei (CDC/Dr Mae Melvin) - Yamada's Gastroenterology

1. Cyst (infective stage): Quadrinucleate cysts are excreted in faeces and are stable in the environment - resistant to chlorine at normal water disinfection doses, but killed by heat (>55°C), drying, or freezing.
2. Excystation: Ingested cysts pass through the stomach (resistant to gastric acid) and excyst in the small intestine, undergoing nuclear and cytoplasmic division to release 8 trophozoites.
3. Trophozoite (tissue-invasive stage): The motile feeding form with a single nucleus and pseudopodia. Trophozoites colonize the large intestine, invade the submucosa to form flask-shaped ulcers, multiply by binary fission, and produce uninucleate cysts.
4. Portal dissemination: Trophozoites enter the portal circulation, become trapped in interlobular veins of the liver, multiply in portal triads, and cause focal hepatocyte infarction and liquefactive necrosis via proteolytic enzymes - forming the abscess.
5. Transmission: Only cysts (not trophozoites) transmit the disease. Trophozoites rapidly degenerate outside the body and are destroyed by gastric acid. Humans are the only reservoir.

• Yamada's Textbook of Gastroenterology, 7th ed., p. 3091
• Bailey and Love's Short Practice of Surgery, 28th ed., p. 88
• Park's Textbook of Preventive and Social Medicine

3. Epidemiology

• Global burden: ~500 million people infected with Entamoeba spp. worldwide; ~40 million develop invasive colitis or extraintestinal abscesses; ~50,000 deaths annually. Among parasitic diseases, only cryptosporidiosis, malaria, and schistosomiasis cause comparable mortality.
• Geographic distribution: Most prevalent in Central and South America (especially Mexico), the Indian subcontinent, Indonesia, sub-Saharan and tropical Africa, and South East Asia. Prevalence of E. histolytica in stool samples in high-endemic zones averages ~10%; incidence of ALA can reach 21 per 100,000 population.
• High-risk groups in non-endemic countries: Travelers, immigrants, institutionalized individuals, and men who have sex with men (MSM).
• Sex difference: The prevalence of colonic disease is equal between sexes, but ALA and other extraintestinal disease is 3-10 times more common in men. This case (48-year-old male) fits this pattern exactly.
• Other risk factors for severe disease: Children (especially neonates), pregnant women, malignancy, malnutrition, corticosteroid therapy.
• Socioeconomic link: More closely tied to poor sanitation and low socioeconomic status than to climate. In areas with wet-dry seasons, transmission increases during rains due to cyst survival in water.

• Yamada's Textbook of Gastroenterology, 7th ed.
• Park's Textbook of Preventive and Social Medicine, p. 283-284

4. Pathophysiology

1. Ingestion: Contaminated food/water introduces cysts via the faecal-oral route.
2. Intestinal invasion: Trophozoites invade the colonic submucosa, producing flask-shaped ulcers (wide base, narrow neck) - predominantly in the caecum and ascending colon, then rectum and sigmoid. This stage may be asymptomatic in up to 90% of infected individuals.
3. Portal entry: Trophozoites gain access to the mesenteric venules and are carried via the portal vein to the liver.
4. Hepatic trapping: Trophozoites are filtered and trapped in the interlobular veins and multiply in portal triads.
5. Liquefactive necrosis: Trophozoites produce proteolytic enzymes (cysteine proteases, amoebapores) causing focal infarction and coalescent liquefactive necrosis. The necrotic cavity fills with the characteristic anchovy-sauce fluid.
6. Right lobe predominance (80%): Blood from the superior mesenteric vein flows more directly into the larger right lobe via the portal vein, explaining this anatomical predilection. Left lobe involvement accounts for ~10%; multiple abscesses (as in this case) are the remainder.
7. Chest complications: Abscesses high on the diaphragmatic surface of the right lobe can cause reactive pleural effusion, basal pneumonitis, and even transdiaphragmatic rupture into the pleural space - explaining this patient's dyspnoea and pulmonary infiltrates on initial presentation.
8. Secondary infection: Sterile unless secondarily infected (which causes the pus to become malodorous).

• Bailey and Love's Short Practice of Surgery, 28th ed., p. 88

5. Differential Diagnosis

6. Signs and Symptoms

• Fever (often swinging, as in this patient - 39.5°C)
• Night sweats and rigors
• Anorexia, malaise, weight loss

• Right upper quadrant / right hypochondrial pain (progresses to right shoulder tip pain - diaphragmatic irritation)
• Non-productive cough and dyspnoea (from diaphragmatic elevation/reactive effusion)
• Hiccoughs (diaphragmatic involvement)

• Toxic, ill-appearing, anaemic patient
• Tender hepatomegaly (most consistent finding)
• Tender and bulging intercostal spaces with overlying skin oedema
• Upper abdominal rigidity
• Pleural effusion and basal pneumonitis (late)
• Occasionally jaundice or ascites

• Rupture into pleural cavity (empyema), peritoneal cavity (peritonitis), or pericardial cavity (tamponade - most feared)
• Secondary infection of the abscess
• Amoeboma (chronic granuloma in large bowel from incomplete treatment)

• Leukocytosis with neutrophilia (as in this patient: 25,000/mm³, 84%)
• Elevated ESR and CRP
• Mildly elevated liver enzymes (ALP most consistently raised)
• Anaemia in chronic cases
• Bailey and Love's Short Practice of Surgery, 28th ed.

7. Treatment

Medical (first-line)

• Metronidazole 400-800 mg three times daily for 5-10 days (or tinidazole as an alternative) - this is the tissue amoebicide that kills trophozoites.
• Followed by a luminal amoebicide to eradicate residual cysts in the gut: Paromomycin (500 mg three times daily for 7 days) or diloxanide furoate (500 mg three times daily for 10 days). This step prevents relapse and ongoing transmission.
• In this case: metronidazole + paromomycin - the textbook regimen. Ceftriaxone was added initially for presumed secondary bacterial infection and was discontinued once cultures were negative.

Drainage indications

• Large abscesses (>5 cm): percutaneous needle aspiration or pigtail catheter drainage combined with drug treatment.
• Drainage is recommended when: the abscess is large and at high risk of rupture; there is inadequate response to medical therapy within 72 hours; left lobe abscess (risk of pericardial rupture); suspected secondary infection.
• In this patient, a drain was placed and removed on day 21 as the discharge transitioned from purulent to serosanguinous.

Surgical treatment

• Rupture into pleural, peritoneal, or pericardial cavity
• Acute toxic megacolon (intestinal amoebiasis)
• Severe haemorrhage
• Bailey and Love's Short Practice of Surgery, 28th ed.
• Maingot's Abdominal Operations

8. Prevention

Primary Prevention

1. Sanitation: Safe disposal of human excreta; hand washing after defecation and before eating. This is the single most effective measure.
2. Water supply: Protection from faecal contamination. Note - chlorine at normal doses does NOT kill amoebic cysts. Sand filtration and boiling are more effective. Iodine-based purification tablets (used in military settings) are also effective.
3. Food hygiene: Thorough washing of raw vegetables with detergent in running water; alternatively, soaking in 5-10% acetic acid or full-strength vinegar removes cysts. Uncooked vegetables from fields irrigated with sewage water are a major risk. Food handlers should be screened, treated, and educated.
4. Vector control: Control of flies, cockroaches, and rodents that mechanically transmit cysts.
5. Health education: Long-term community education on personal hygiene.
6. Military-specific: Soldiers deployed to endemic regions should receive pre-deployment health briefings, use water purification beyond chlorination alone, and practice strict food/hand hygiene.

Secondary Prevention

• Early diagnosis of symptomatic and carrier individuals.
• Treatment of asymptomatic carriers (luminal agents like paromomycin) to interrupt transmission.
• Periodic screening of food handlers in endemic areas.
• Contact tracing within households (amoebiasis is frequently a household infection - when one member is infected, others may also be affected).
• Park's Textbook of Preventive and Social Medicine, p. 284

9. Conclusion

• Delayed diagnosis is common because initial presentation with fever, dyspnoea, and interstitial infiltrates mimics community-acquired pneumonia. ALA should be considered in any patient from or traveling to an endemic region who does not respond to standard antibiotics for CAP.
• PCR of abscess material is the key diagnostic tool when cultures are negative - it was diagnostic in this case.
• Medical therapy is highly effective: metronidazole as the tissue agent followed by paromomycin as the luminal agent is the standard regimen. This patient was successfully treated without surgery.
• Drainage is needed for large/complex abscesses - this patient required percutaneous drainage with drain removal on day 21.
• Post-treatment negative stool antigen and PCR confirmed microbiological cure.
• Prevention in military/travel settings hinges on water boiling/filtration (not chlorination alone), food hygiene, and sanitation - all critical for deployed personnel in endemic zones.

Sources: Bailey and Love's Short Practice of Surgery, 28th ed. | Yamada's Textbook of Gastroenterology, 7th ed. | Park's Textbook of Preventive and Social Medicine | Maingot's Abdominal Operations | Ghalib et al. 2025, Int Microbiol [PMID: 39979548]