AMOEBIASIS

INTRODUCTION

Amoebiasis is an intestinal infection caused by the protozoan parasite Entamoeba histolytica.

It spreads mainly through:

• Poor sanitation
• Contaminated food and drinking water

Epidemiology

• Third leading cause of death among parasitic infections (after malaria and schistosomiasis)
• Infection rate in developing countries: 30–40%
• In India: ~15% prevalence
• More common in urban slums

ETIOPATHOGENESIS

Forms of the parasite

1. Trophozoite (active form)
2. Cyst (infective form)

Life Cycle & Pathogenesis

• Infection begins by ingestion of cysts in contaminated food/water
• Cysts survive gastric acidity and reach intestine
• In the ileocecal region, excystation occurs → each cyst releases 8 trophozoites
• Trophozoites:
• Size: 20–60 µm
• Contain vacuoles and nucleus with central nucleolus
• Multiply in colon

Outcomes

• Most cases: asymptomatic (commensal state)
• Some cases:
• Invade intestinal mucosa → amoebic dysentery
• Cause flask-shaped ulcers in caecum and ascending colon

Extra-intestinal spread

• Via bloodstream → liver, lungs, brain
• Leads to amoebic abscesses (especially liver)

Transmission

• Cysts passed in feces → survive long outside
• Trophozoites die quickly → not infective

Reservoir

• Asymptomatic carriers (may excrete millions of cysts/day)

CLINICAL FEATURES

Common Symptoms

• Fever
• Abdominal pain and discomfort
• Diarrhea with blood and mucus
• Foul-smelling stool
• Alternating diarrhea and constipation
• Irregular bowel habits

Other Features

• Perianal ulceration
• Genital lesions (rare, after anal intercourse)

Complications

Amoebic Liver Abscess

• Right upper quadrant pain
• Fever (mild to moderate)
• Hepatomegaly
• Weakness

DIAGNOSIS

Primary Method

• Stool microscopy:
• Detection of cysts/trophozoites

Sensitivity

• Single sample: ~50%
• Multiple samples (over 10 days): 85–95%

Advanced Investigations

• Ultrasound (USG)
• CT scan
• MRI

Other Methods

• Proctoscopy / sigmoidoscopy
• Biopsy (in complicated cases)

TREATMENT

Supportive Care

• Oral rehydration therapy (ORS)
• Electrolyte replacement
• Nutritional support

Surgical Management

• For large liver abscess:
• Needle aspiration
• Catheter drainage
• Rarely surgery

Anti-amoebic Drugs

1. Luminal Amoebicides

(Act in intestine)

• Diloxanide furoate
• Iodoquinol
• Paromomycin

2. Tissue Amoebicides

(Act in tissues)

• Metronidazole
• Tinidazole
• Tetracycline
• Dihydroemetine
• Chloroquine

Standard Treatment Regimens

Intestinal Amoebiasis / Liver Abscess

• Metronidazole:
• 800 mg TID for 7 days
• OR Tinidazole:
• 2 g once daily for 3–5 days
• PLUS Diloxanide furoate:
• 500 mg TID for 10 days

Non-responsive Cases

• Add Tetracycline:
• 500 mg QID for 5 days
• Then 250 mg QID for 5 days
  ⚠ Avoid in pregnancy & lactation

Liver Abscess (Not responding)

• Chloroquine:
• 2 tablets BID for 2 days
• Then 1 tablet BID for 2–3 weeks

OR

• Dihydroemetine:
• 1–1.5 mg/kg/day for 5 days

Asymptomatic Cyst Passers

• Iodoquinol:
• 650 mg TID for 20 days

PATIENT EDUCATION

About Disease

• Caused by contaminated food/water
• Communicable but curable
• Common symptoms: diarrhea, abdominal pain

High-Risk Groups

• Children
• Malnourished individuals
• Immunocompromised patients
• Pregnant women

Medication Advice

• Complete full course
• Do not skip doses
• Do not double dose

Important Side Effects

• Metronidazole/Tinidazole:
• Metallic taste
• Chloroquine:
• Palpitations
• Ear ringing (seek doctor immediately)

LIFESTYLE MODIFICATIONS

• Maintain hand hygiene
• Avoid food handling during illness
• Use clean toilets
• Avoid sharing towels
• Drink safe water
• Avoid unpasteurized dairy
• Avoid open defecation

PREVENTION

• Proper sanitation
• Hand washing
• Safe drinking water
• Avoid raw/street food
• Safe travel practices

⚠ No vaccine available yet

EXAM QUICK POINTS (VERY IMPORTANT)

• Infective form → Cyst
• Diagnostic test → Stool microscopy
• Drug of choice → Metronidazole
• Complication → Liver abscess
• Ulcer type → Flask-shaped ulcer
• Reservoir → Asymptomatic carrier