Paediatrics chapters
Giardiasis and amoebiasis
The two important intestinal protozoa of children: Giardia lamblia, which causes greasy, foul diarrhoea and malabsorption, and Entamoeba histolytica, which causes amoebic dysentery and liver abscess, with diagnosis, imaging and treatment.
- Giardia lamblia is a flagellate spread by cysts in water and on hands; trophozoites stick to the duodenal and jejunal lining and cause watery, greasy, foul stools without blood, bloating and, if chronic, malabsorption, lactose intolerance and weight loss; diagnose by cysts or trophozoites in stool (repeated samples) or stool antigen; treat with metronidazole, tinidazole or nitazoxanide.
- Entamoeba histolytica is spread by cysts; trophozoites invade the colon, making flask-shaped ulcers and bloody mucoid diarrhoea with few pus cells, and can reach the liver to form an abscess.
- Diagnose by red-cell-containing trophozoites in fresh stool, stool antigen and serology; image the liver with ultrasound (or CT); treat with metronidazole followed by a luminal agent (diloxanide furoate, paromomycin or iodoquinol); drain large or threatening abscesses.
On this page
Overview
Giardia lamblia and Entamoeba histolytica are the protozoa that matter most for children's guts in Pakistan. Both spread through cysts in faecally contaminated water, food and hands. They behave very differently:
- Giardia stays on the small-bowel surface: no blood, but malabsorption.
- Entamoeba invades the colon: dysentery and, sometimes, liver abscess.
Questions test the organism, the stool picture, the diagnostic test, imaging of liver abscess and the drugs.
Giardiasis
Causative protozoan
- Giardia lamblia (also called G. intestinalis or G. duodenalis), a flagellated protozoan.
- Two forms: the cyst (infective, hardy, survives in water) and the trophozoite (causes disease).
- After ingestion, cysts release trophozoites, which adhere to the microvilli of the duodenum and jejunum.
- Spread: person to person (day care, families) and contaminated water; a few cysts are enough.
- Rare in neonates; can occur at any age.
Akbar calls giardiasis the commonest protozoal cause of chronic, relapsing diarrhoea in children.
Clinical features
| Form | Features |
|---|---|
| Asymptomatic | Common; cyst passers spread the infection |
| Acute | Starts 1-2 weeks after infection: sudden watery or greasy, foul-smelling stools, flatulence, bloating, nausea, cramps; fever usually absent |
| Chronic | Bouts of foul, greasy diarrhoea alternating with constipation or normal stools, malaise, anorexia, diffuse abdominal pain, weight loss and failure to thrive |
Complications of chronic infection:
- Malabsorption and steatorrhoea.
- Secondary lactose intolerance.
- Vitamin A and iron deficiency.
Children with immune deficiency (especially antibody deficiency) get severe, persistent giardiasis.
Giardia stools contain no blood, no mucus, no pus cells and no eosinophils. Bloody diarrhoea points away from Giardia.
Diagnosis: stool cysts and trophozoites
- Stool microscopy: trophozoites or cysts in a fresh specimen. Liquid stools give the best yield of trophozoites; formed stools usually show cysts.
- Excretion is intermittent, so Nelson advises three stool specimens before calling microscopy negative.
- Stool antigen tests (immunofluorescence or enzyme immunoassay) are more sensitive and specific; Nelson calls them the diagnostic tests of choice.
- Duodenal aspirate or biopsy is rarely needed.
Treatment (Akbar)
| Drug | Dose and notes |
|---|---|
| Metronidazole | Drug of choice in Akbar; 15 mg/kg/day, split three times a day, for 5 days |
| Tinidazole | 50 mg/kg as a single dose in children over 3 years |
| Nitazoxanide | 1-3 years: 100 mg twice daily for 3 days; 4-11 years: 200 mg twice daily for 3 days |
| Albendazole | Alternative over 6 years (Akbar: 400 mg once daily for 5 days) |
| Furazolidone, quinacrine | Older alternatives |
- Treatment failure or relapse: repeat the same drug or switch to another; both work equally well.
- Treat lactose intolerance (temporary lactose reduction) and correct deficiencies.
Giardia and Entamoeba cysts resist ordinary chlorination; boiling and filtration make water safe.
Prevention
- Treat water: boil drinking water (Akbar advises more than 10 minutes) or filter it.
- Hand washing, especially in nurseries and day care.
- Avoid uncooked, unwashed food.
- Symptomatic and sometimes asymptomatic carriers in the family may need treatment.
Amoebiasis
Causative organism
- Entamoeba histolytica, a protozoan with trophozoite and cyst forms.
- Cysts are the infective form. They resist ordinary water chlorination but are killed by drying, heating and boiling and removed by filtration (Park).
- Trophozoites are killed by stomach acid and do not transmit infection.
- Spread: faecal-oral, often from asymptomatic cyst passers, especially food handlers; water, raw vegetables, flies and hands.
- Most infections (over 90%) cause no symptoms (Park).
Pathogenesis
- In the colon, the cyst releases trophozoites, which invade the mucosa, mainly in the caecum and ascending colon, then rectum and sigmoid.
- Invasion produces characteristic flask-shaped ulcers (narrow neck, wide base).
- Trophozoites can enter the portal circulation and reach the liver, and less often the lung and brain.
Clinical features
| Form | Features |
|---|---|
| Asymptomatic cyst passage | Commonest; source of infection |
| Acute amoebic colitis (dysentery) | 1-2 week history of loose stools with blood and mucus, abdominal pain, tenesmus; some children are febrile or dehydrated; tenderness in the lower abdomen |
| Chronic non-dysenteric colitis | Recurrent bloody diarrhoea over months or years, weight loss |
| Amoeboma | Inflammatory mass in the colon that can mimic a tumour |
| Extra-intestinal | Liver abscess (commonest), lung and brain abscess |
| Complications | Perforation, haemorrhage, peritonitis |
Diagnostic investigations
- Fresh stool microscopy (examined warm and quickly): trophozoites containing ingested red cells (haematophagous trophozoites) prove invasive E. histolytica. Cysts alone may be non-pathogenic species.
- Occult blood is present in almost every case of amoebic colitis, but faecal white cells are few.
- Stool antigen test for E. histolytica.
- Serology (ELISA, indirect haemagglutination): most useful in extra-intestinal disease; often negative in purely intestinal infection.
- Colonoscopy and biopsy when the picture is unclear (ulcers, amoeboma).
Few pus cells in a bloody stool favours amoebic over bacillary dysentery; the clincher is red cells inside the trophozoites.
Amoebic liver abscess
Clinical features (Akbar)
- Fever, chills, malaise, weight loss, right upper abdominal pain.
- Enlarged, tender liver, with constant dull pain.
- Jaundice is uncommon.
- Raised right hemidiaphragm with reduced movement; right basal lung changes (consolidation in about 30%).
- Cough, breathlessness or shoulder-tip pain if the abscess threatens the chest.
- Often no current diarrhoea; stools are negative for amoebae in more than half.
Investigations and imaging
| Test | Finding |
|---|---|
| Blood count | Raised white count, anaemia, high ESR |
| Liver function tests | Normal or mild rise in transaminases and alkaline phosphatase |
| Ultrasound | First imaging test: shows the abscess, its size, number and site, and guides aspiration |
| CT scan | Alternative or when ultrasound is unclear; better for complications |
| Chest X-ray | Raised right hemidiaphragm, right basal changes or effusion |
| Serology (haemagglutination) | Positive in more than 95% of amoebic liver disease (Akbar) |
| Ultrasound-guided aspiration | Usually diagnostic; separates amoebic from pyogenic abscess |
A negative stool examination does not exclude an amoebic liver abscess; serology plus ultrasound is the usual route to diagnosis.
Differential diagnosis: pyogenic liver abscess (Staph. aureus, E. coli, anaerobes; Akbar notes blood culture is positive in up to 60% of pyogenic abscesses), hydatid cyst, hepatoma, hepatitis, subphrenic abscess, pneumonia or empyema.
Complications
- Rupture into the peritoneum, pleura, lung or pericardium.
- Secondary bacterial infection (10-20% in Akbar).
- Spread to the lungs and brain.
Treatment of amoebiasis
Principle
Two stages:
- A tissue amoebicide to kill invading trophozoites: metronidazole (or tinidazole).
- A luminal amoebicide to clear cysts left in the bowel and prevent relapse and spread.
Drugs (Akbar)
| Drug | Role | Dose |
|---|---|---|
| Metronidazole | Colitis and liver abscess | 35-50 mg/kg/day in 3 doses for 7-10 days (Akbar), then a luminal drug |
| Tinidazole | Alternative to metronidazole | - |
| Diloxanide furoate | Luminal | 20 mg/kg/day in 3 doses for 7 days |
| Paromomycin | Luminal | 25-35 mg/kg/day in 3 doses for 7 days |
| Iodoquinol | Luminal | 30-40 mg/kg/day in 3 doses for 20 days |
- Asymptomatic cyst passers: a luminal drug alone. Park notes that in endemic areas they are usually treated only if they are food handlers (reinfection is likely).
- Severe liver disease: Akbar mentions dehydroemetine with chloroquine as additions.
Liver abscess: beyond drugs
- Most respond to metronidazole within days.
- Ultrasound-guided aspiration or drainage: large abscess, risk of rupture, no response to drugs, or doubt about the diagnosis.
- Surgery: rupture outside the liver capsule or fistula.
- The cavity usually resolves over 3-6 months; Akbar quotes a cure rate of about 90% with proper treatment, while an unrecognised abscess is fatal.
"Kill in the tissue, clean the lumen": metronidazole for the invaders, diloxanide or paromomycin for the cysts.
Prevention
- Sanitary disposal of faeces and hand washing after defecation and before eating.
- Boil or filter drinking water (chlorination alone is not enough for cysts).
- Wash raw vegetables and fruit well; eat cooked or peeled food.
- Screen and treat food handlers; enteric precautions for patients.
Giardiasis and amoebiasis compared
| Feature | Giardiasis | Amoebiasis |
|---|---|---|
| Site | Duodenum, jejunum | Colon (caecum first), liver |
| Mechanism | Adheres to surface; no invasion | Invades; flask-shaped ulcers |
| Stool | Watery or greasy, foul, no blood | Blood and mucus, few pus cells |
| Key complication | Malabsorption, lactose intolerance, failure to thrive | Liver abscess, perforation |
| Diagnosis | Cysts or trophozoites, stool antigen | Haematophagous trophozoites, antigen, serology, ultrasound |
| Treatment | Metronidazole, tinidazole, nitazoxanide | Metronidazole then a luminal agent |
Expect: Giardia as a flagellate in the duodenum spread by cysts; greasy foul stools without blood, bloating, malabsorption, lactose intolerance and failure to thrive; diagnosis by cysts or trophozoites in repeated stools or by antigen tests; metronidazole, tinidazole or nitazoxanide. For E. histolytica: cyst as infective form, invasion of the caecum with flask-shaped ulcers, bloody mucoid stools with few pus cells, haematophagous trophozoites, serology for extra-intestinal disease, ultrasound for liver abscess with raised right hemidiaphragm on X-ray, and metronidazole followed by a luminal drug, with aspiration for large abscesses.
Quick revision
- Both spread by cysts; both treated with metronidazole.
- Giardia: duodenum; foul greasy stools, no blood; malabsorption, lactose intolerance.
- Giardia diagnosis: cysts or trophozoites in 3 stools; stool antigen best.
- Giardia drugs: metronidazole, tinidazole 50 mg/kg once (over 3 years), nitazoxanide.
- E. histolytica: caecum; flask-shaped ulcers; bloody mucoid stools, few pus cells.
- Diagnosis: red-cell-containing trophozoites; antigen; serology for liver disease.
- Liver abscess: fever, tender liver, raised right diaphragm; ultrasound first; stools often negative.
- Metronidazole then diloxanide, paromomycin or iodoquinol; aspirate large abscesses.
Written by The House Job from standard references (Basis of Paediatrics by Pervez Akbar; Nelson Essentials of Paediatrics; Park's Preventive and Social Medicine).
FAQ
Why does giardiasis cause malabsorption without blood in the stool?
The trophozoites coat and damage the small-bowel surface without invading it, so absorption of fat, lactose and nutrients falls but there is no ulceration or bleeding.
Why is a luminal drug needed after metronidazole?
Metronidazole kills invading trophozoites but leaves cysts in the bowel lumen. A luminal drug clears these, preventing relapse and spread to others.
Does a normal stool test rule out amoebic liver abscess?
No. Stools are negative in more than half of children with an amoebic liver abscess; ultrasound and serology make the diagnosis.
When is an amoebic liver abscess drained?
When it is large or likely to rupture, when the child does not improve on drugs, or when it must be separated from a pyogenic abscess.