Entamoeba histolytica

Background

Microbiology

• Intestinal protozoan parasite within the genus Entamoeba
• Microscopically distinguishable from the non-pathogenic E. dispar, E. moshkovskii, and E. bangladeshii

Epidemiology

• Present worldwide, but most disease occurs in the developing world
• Causes 34 to 50 million cases annually and up to 100,000 deaths

Clinical Manifestations

Amoebic Diarrhea and Dysentery

• Amoebic diarrhea, with or without dysentery, is common
  • About 15 to 30% of cases involve amoebic dysentery (with macroscopic or microscopic blood)
• Typically a subacute onset over 3 to 4 weeks and abdominal pain
  • However, can be up to months
• Fever is rare, even in dysentery
• In children, can lead to intussusception, perforation, and necrotizing colitis

Amoebic Liver Abscess

• Amoebic liver abscess is far more common in men than women, and rare in children
• Symptoms progress over 2 to 4 weeks, with fever (80%) and abdominal pain (80%)
  • Right upper quadrant tenderness (75%), weight loss (40%), diarrhea (15-35%), cough (10%), and jaundice (10-15%)
  • The pain is typically a dull ache in the right upper quadrant or epigastrium
• More likely to present with abdominal pain and right upper quadrant tenderness than pyogenic liver abscess

Disseminated Amoebiasis

• Metastatic infections are possible, most often from direct extension of a liver abscess
• Most commonly spreads to chest, with empyema, bronchohepatic fistula, pericarditis
• Cerebral disease is rare but can happen

Diagnosis

• Microscopically indistinguishable from the non-pathogenic E. dispar, so needs molecular tests to confirm diagnosis
• On aspiration, the fluid is classically odorless, thick, yellow-brown liquid, described as "anchovy paste"

Management

Diarrhea or Dysentery

• Either
  • Metronidazole 750 mg p.o. tid for 5 to 10 days
  • Tinidazole 2 g PO daily for 3-5 days
• Followed by a luminal agent, as below

Liver Abscess

• Either
  • Metronidazole 750 mg PO tid for 10 days, or
  • Tinidazole 2 g PO daily for 5 days
• Followed by a luminal agent:
  • Paramomycin 500 mg p.o. tid for 7 days
  • Iodoquinol 650 mg p.o. tid for 20 days
  • Diloxanide furoate 500 mg p.o. tid for 10 days
• May need surgery or aspiration if the lesion is large or medication has failed

Asymptomatic Carriage

• Treat with a luminal agent, as above

Treatments in Canada

• Metronidazole, iodoquinol, and paromomycin are all available in Canada

Further Reading

• Adrienne J. Showler, Andrea K. Boggild. Entamoeba histolytica. CMAJ Sep 2013, 185 (12) 1064; DOI: 10.1503/cmaj.121576