Amoebiasis is an intestinal infection caused by the protozoan parasite Entamoeba histolytica. It spreads mainly through contaminated food, unsafe drinking water and poor sanitation. Globally, amoebiasis is one of the top three causes of death from parasitic infections, after malaria and schistosomiasis. In developing countries, infection rates may reach 30–40%. In India, the prevalence is around 15%.
Etiology and Lifecycle
The parasite exists in two forms:
- Trophozoite (active form) – causes disease.
- Cyst (dormant form) – responsible for transmission.
Lifecycle Overview
- Infection begins when a person consumes food or water contaminated with cysts.
- The cysts survive stomach acid and reach the intestine.
- In the ileocecal region, the cysts undergo excystation, releasing 8 trophozoites.
- Trophozoites multiply and may live harmlessly in many people.
- In some, they invade the intestinal mucosa, forming flask-shaped ulcers and causing dysentery.
- Trophozoites may spread to the liver, lungs or brain through the bloodstream and form life-threatening abscesses.
- Inside the intestine, some trophozoites convert back to cysts, which are passed in stool.
A carrier can excrete millions of cysts per day, contributing significantly to community spread.
Clinical Features
Most infected people are asymptomatic carriers. Symptomatic amoebiasis ranges from mild abdominal discomfort to severe dysentery.
Common Symptoms
- Fever
- Abdominal pain and cramps
- Diarrhoea with blood or mucus
- Offensive stool odor
- Alternating diarrhoea and constipation
- Irregular bowel habits
Other Features
- Perianal skin ulcers
- Penile lesions in men engaging in anal intercourse
Hepatic Amoebiasis
The most serious complication is amoebic liver abscess. Symptoms include:
- Pain in the right upper abdomen
- Fever (mild to moderate)
- Weight loss and fatigue
- Hepatomegaly
Diagnosis
Stool Examination
- Microscopy is the primary diagnostic method.
- A single sample has ~50% sensitivity; examining 3 samples over 10 days increases sensitivity to 85–95%.
- Trophozoites with ingested RBCs strongly suggest invasive disease.
Imaging
Used when liver involvement is suspected:
- Ultrasound
- CT scan
- MRI
Endoscopic Procedures
- Proctoscopy or sigmoidoscopy
- Colonoscopy with biopsy if needed
Treatment
Amoebiasis treatment includes hydration, electrolyte replacement and antiparasitic drugs. Large liver abscesses may require aspiration or drainage.
Drug Classifications
- Luminal amoebicides – eliminate cysts from intestine
- Iodoquinol
- Diloxanide furoate
- Paromomycin
- Tissue amoebicides – act on invasive disease
- Metronidazole
- Tinidazole
- Tetracycline
- Dihydroemetine
- Chloroquine
Recommended Regimens (Summarized)
1) Intestinal Amoebiasis / Amoebic Liver Abscess
- Metronidazole 800 mg three times daily for 7 days (or IV 500 mg if severe condition).
- Tinidazole 2 g once daily for 3–5 days.
- Diloxanide furoate 500 mg three times daily for 10 days (luminal coverage).
2) Resistant Cases
- Tetracycline 500 mg four times daily for 5 days, then 250 mg four times daily for 5 days.
- Avoid in pregnancy and breastfeeding.
3) Liver Abscess Not Responding to Metronidazole
- Chloroquine 2 tablets twice daily for 2 days, then 1 tablet twice daily for 19 days.
- Dihydroemetine 1–1.5 mg/kg/day for 5 days (max 90 mg/day).
4) Asymptomatic Cyst Passers
- Iodoquinol 650 mg three times daily for 20 days.
Patient Education
About the Disease
- Amoebiasis occurs when contaminated food or water is consumed.
- It is curable with proper treatment.
- Symptoms include abdominal pain, diarrhoea with blood/mucus and weakness.
- Higher risk in malnourished individuals, infants, pregnant women and people with low immunity.
About the Medications
- Medicines must be taken regularly without missing doses.
- If a dose is missed, skip doubling and continue the next dose normally.
- Metronidazole and tinidazole may cause metallic taste.
- If taking chloroquine, watch for palpitations or ringing in the ears and report immediately.
Lifestyle Modifications
- Avoid attending work or school until symptoms settle to prevent spreading cysts.
- Wash hands thoroughly after using toilets and before cooking or eating.
- Use clean toilets and avoid sharing towels.
- Avoid unpasteurized milk and dairy products.
- Do not defecate in open water bodies.
- While travelling, drink only packaged or boiled water.
Prevention
- Good personal hygiene and handwashing.
- Drink safe water — bottled, boiled or filtered.
- Avoid raw or street food in low-sanitation areas.
- Proper waste disposal and clean bathrooms.
- Safe sexual practices; avoid sexual contact until infection resolves.
- No approved vaccine yet, but research is ongoing.
Detailed Notes:
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