Overview
Entamoeba histolytica is a parasitic protozoan that can cause amoebiasis, an infection due to amoebae, which can be asymptomatic or cause disease in the liver or colon. Amoebiasis is more common in the tropics and less common in developed countries.
Amoebic dysentery is an intestinal amoebic infection which may be associated with an infection of distant sites, particularly the liver. It can have a long incubation period of around 2-4 weeks.
Pathophysiology
Entamoeba histolytica is spread by the faecal-oral route and upon ingestion, it infects the colon, causing dysentery. Over time, cysts are passed out in the faeces.
Risk Factors
Risk factors include poverty, poor sanitation, and overcrowding. People who are immunosuppressed and/or pregnant are at an increased risk of severe disease.
Presentation
Amoebic dysentery
Amoebic dysentery may be asymptomatic. Features present gradually with:
- Profuse bloody diarrhoea
- Abdominal pain
- Complications – toxic megacolon, fulminant colitis, and perianal ulceration
Amoebic liver abscess
Amoebic liver abscess is the most common extraintestinal manifestation. Its features can include:
- Right upper quadrant pain with constitutional symptoms features (e.g. fever, fatigue, malaise, anorexia, and weight loss) and hepatomegaly
- Abscess rupture – this may cause peritonitis or pleural infection
Diagnosis
Amoebic dysentery
Key tests for amoebic dysentery include:
- Stool microscopy – may show trophozoites, however, this requires an examination if the stool is kept warm (‘hot stool’) or examined shortly after the sample is produced
- Polymerase chain reaction for DNA – the test of choice where available, often performed to confirm the diagnosis if microscopy is positive
- Serology testing – high sensitivity (>90%), but cannot distinguish between acute or previous infection
Amoebic liver abscess
- Liver ultrasound – identifies a lesion that is often homogenous and round
- Liver aspiration – the contents of the cyst are viscous and red, often described as ‘anchovy sauce’
- Polymerase chain reaction for DNA – the test of choice where available
- Serology testing – high sensitivity (>90%), but cannot distinguish between acute or previous infection
Management
Overview
Treatment often involves oral metronidazole and a luminal agent (drugs that mainly act on parasites within the lumen) such as diloxanide furoate.
