Pathogenic Ameba

• Ingestion of Cyst

  1. Cyst goes to stomach

  2. Excystation takes place

  3. pH should be alkaline or neutral (acidic pH does not favor formation of trophozoites)
• Multiplication of Trophozoites

  1. Takes place in large intestine

  2. Multiplication through binary fission

  3. Usually produces 4 trophozoites from 1 cyst (but not for all organisms!)
• Trophozoites and Cysts go to the stool

  Whether trophozoites or cysts appear depends on the type of stool (if formed or watery)
• Entamoeba histolytica


  • MOT: ingestion of infective cyst
  • Habitat: large intestine
  • Only pathogenic amoeba
  • Subphylum Sarcodina, superclass Rhizopoda, class Lobosea, order Amoebida, family Entamoebidae
• Cyst


  • Resistant to gastric acidity and desiccation, can survive in a moist environment for several weeks
• Trophozoite of E. histolytica


  • 1 nucleus (vesicular appearance)
  • Centrally located karyosome
  • Fine, evenly distributed peripheral chromatin
  • Clean-looking cytoplasm
  • Finger-like appearance of pseudopodia
  • Hematophagus: presence of ingested RBCs
• Cyst of E. histolytica


  • 4 nuclei (ideally)
  • Small, centrally located karyosome
  • Fine, evenly distributed peripheral chromatin
  • Thin wall, hyaline appearance, highly refractile
  • Chromatoidal bar
  • Food reserve, energy stores
  • Chemical composition: crystalline RNA
  • Shape: sausage or cigar shaped
  • Also has a glycogen vacuole
• Non-pathogenic E. histolytica look-alikes

  • E. dispar
  • E. moshkovskii (also called Laredo strain)
  • E. Bangladeshi (all human isolates of this belongs to group ribodeme 2)
• Non-pathogenic E. histolytica look-alikes

  • Morphologically the same with E. histolytica, but grows in room temp (E. histolytica grows at 37 degrees Celsius)
  • Can be differentiated through molecular techniques, isoenzyme analysis, zymodeme analysis, and checking the trophozoites for ingested RBCs
• Ova and Parasite Examination of Stool

  • Minimum of three stool specimens collected on different days
  • Direct Fecal Smear
  • Concentration Techniques (FECT, MIFC)
  • Permanent Stained Smear (Iron Hematoxylin, Trichrome Stain, Saline and methylene blue, Saline and iodine)
  • Charcot-Leyden crystals can be seen in the stool
• Entamoeba histolytica


  Causative agent of amebiasis
• Intestinal Disease


  1. Incubation period: 1-4 weeks

  2. Bloody diarrhea, dysentery (majority of cases), abdominal pain, flatulence, weight loss, chronic fatigue

  3. Release of enzymes to lyse mucosal lining

  4. Formation of flask-shaped ulcers by the trophozoites

  5. Excess mucus in stool

  6. Tenesmus: cramping rectal pain

  7. 10 bowel movements per day
• Clinical Forms of Intestinal Disease

  • Fulminating Colitis (inflammation of colon); Can lead to perforation and secondary bacterial peritonitis (most serious complications)
  • Amebic Appendicitis
  • Ameboma (granulomas, chronic inflammations, can be mistaken as carcinomas or cancer)
• Fulminating Colitis


  • Can lead to perforation and secondary bacterial peritonitis (most serious complications)
• Extra-intestinal Disease


  1. Amebic Liver Abscess (ALA): liver aspirate (like anchovy sauce) where you can find trophozoites

  2. Can lead to rupture into the pericardium, rupture into the pleura, super infection, and intraperitoneal rupture

  3. Cardinal signs: fever and right upper quadrant pain

  4. Tender liver (tender: painful when you touch or palpate)

  5. Hepatomegaly (abnormal enlargement of liver)
• Cutaneous Amebiasis


  • Rare, infection of skin and soft tissue
  • Skin rupture
  • Affects inguinal areas
  • Can be transmitted sexually
  • Amebiasis is characterized by low amount of WBCs in stool
  • Can cause lung abscess (found in sputum) and brain abscess
• Secondary amebic meningoencephalitis (occurs in 1-2%)
• Amebiasis


  • Is different from bacterial dysentery
  • In amebiasis, there is mucus and blood in the stool
  • There is no granulocytosis and no high fever
  • There is also a fishy smell of the stool