Amoebiasis

Entamoeba histolytica

epidemiology

• worldwide
• 40-50 mil. symptomatic cases per year
• number of asymptomatic cases unknown
• 40,000-50,000 per year
• sexual transmission in developed countries

life cycle and pathophysiology

• feco-oral infection of cyst
• hutch in small intestine into trophozoite
• reside in large intestine
• propagate by binary fission
• some penetrate large intestine wall
  • bloody diarrea
  • trophozoites phagocityze RBC
  • only RBC phagocitizing trophozoite means infection
  • non-RBC-phagocitizing trophozoite means colonization
• some invade into portal vein through liver
  • liver abscess
• some encyst in large intestine
• cysts are excreted from anus

clinical manifestation

• incubation a few days to years
• 80% of infection are asymptomatic
• mild, extensive, extreme
• large intestine ulcer
  • flask-shaped ulcer in histpathology
• advanced disease mimics ulcerative colitis and Crohn's disease

amoebic liver abscess (ALA)

• right lobe: left lobe =4:1
• male: female=10:1
• all age groups
  • most common in 20-40 y/o
• >50% of patients have no previous dysentery

morphology

• trophozoite 20-50 μm
• cyst has 4 nuclei, each nucleus has a nucleolus

treatment

• metronidazole for trophozoite
• paromomycin for cyst eradication

Entamoeba dispar

• formerly named as E. histolytica in 1903
• non-pathogenic type of old E. histolytica was distinguished as E. dispar in 1925

distribution

• E. disper vs E. histolytica
  • 3:1 in developing countries
  • 10:1 in developed countries

Entamoeba coli

• 6 nuclei in cyst