3. AMOEBA

• Copulatory organs of nematodes parasites include spicule and gubernaculum
• Apical complex is necessary for attachment to the host
• Cyclophyllidean tapeworm has open-ended uterus
• Aberant parasite is parasite that migrate and reach the site of the host but it cannot live or develop further
• Starch granules are artifact that appears as irregular shaped
• Life cycle, mode of infection, disease, infective stage and important identifying features of diagnostic stage

  • Amoeba
  • Protozoa
  • Intestinal Amoeba
  • Entamoeba histolytica
  • Entamoeba coli
  • Endolimax nana
  • Iodamoeba butschli
  • Blastocystis hominis
  • Free living Amoeba
  • Naegleria fowleri
  • Acanthamoeba spp.
  • Intestinal and atrial flagelates and ciliates
  • Giardia lamblia
  • Dientamoeba fragilis
  • Trichomonas vaginalis
  • Balantidium coli
  • Blood and tissue flagelates
  • Leishmania spp.
  • Trypanosoma sp.
  • Blood and tissue sporozoa
  • Plasmodium vivax
  • Plasmodium ovale
  • Plasmodium malariae
  • Plasmodium falciparum
  • Plasmodium knowlesi
  • Babesiosis
  • Toxoplasma gondii
  • Pneumocystis carinii

  
• Amoeba


  • Classified under protozoa
  • Do not have fixed shape
  • Extension of pseudopodia for motility (locomotion) and engulfment food by phagocytosis
  • Cytoplasm is bounded by a membrane
  • Outer ectoplasm
  • Inner endoplasm
  • Free living and parasitic amoeba
  • Parasitic amoeba causes amoebiasis or infection due to amoeba
  • Commonly found in human is Entamoeba, Endolimax and Iodamoeba
  • Motility: crawling or gliding

  
• Amoeba reproduction


  • Fusion and budding
  • Cysts: Infective form for vertebrate host

  
• Entamoeba histolytica


  • Pathogenic intestinal amoeba
  • Distribution: Worldwide, common in tropical areas of Asia, Africa and Latin America
  • Mode of infection: Ingestion of water and food containing cysts, oral-fecal route
• Entamoeba histolytica trophozoite


  • Size range: 8-65µm (irregular shape)
  • Actively motile with fingerlike pseudopodia
  • 1 nucleus
  • Karyosome: Small and central
  • Peripheral chromatin: Fine and evenly distributed
  • Cytoplasm: Finely granular, contains ingested RBC
  • Site: Lumen
• Entamoeba histolytica trophozoite


  • Ectoplasm: Clear, transparent, refractile
  • Endoplasm: Finely granular, having ground glass appearance, contains nucleus, food vacuoles, erythrocytes, leucocytes, tissue debris
  • Pseudopodia: Sudden jerky movement of ectoplasm in one direction, then streaming in of the whole endoplasm

  
• Entamoeba histolytica nucleus


  • Spherical, 4-6µm
  • Contains central karyosome, chromatin granules (evenly distributed)
  • Not clearly seen in living trophozoites
  • Stained with iron-hematoxylin
• Entamoeba histolytica trophozoite life span


  • Up to 5 hours at 37°C
  • Killed by drying, heat, chemical sterilization
  • Ingestion: Destroyed in stomach, cannot cause infection
  • Infection is not transmitted by trophozoites

  
• Entamoeba histolytica trophozoite


  • Iron-hematoxylin staining
  • Trichrome staining
  • In iodine - direct wet mount
• Entamoeba histolytica cyst


  • Size range: 8-20µm
  • Spherical to round shape
  • 1 to 4 nuclei (immature: 1; mature: 4)
  • Karyosome: Small and central
  • Peripheral chromatin: Fine and evenly distributed
  • Cytoplasm: Finely granular
  • Cytoplasmic inclusions: Chromatoid bars/rounded ends, Diffuse glycogen mass (seen in immature cyst, disappear in mature cyst)

  
• Entamoeba histolytica cyst


  • Unstained wet mount: Chromatoid bodies with blunt, rounded ends, nucleus not clearly seen
  • Iron hematoxylin stain: Chromatoid bodies appear deep blue or black, glycogen mass appears unstained
  • Iodine: Glycogen mass appears golden brown
  • Trichrome stain: 2-3 nuclei visible, chromatoid bars with typically blunted ends
• Entamoeba histolytica life cycle

  1. Mature cyst (infective form) ingested through water or food

  2. Excystation occurs when cyst reaches lower part of small intestine

  3. Trophozoites multiply in submucous tissue of large intestine by binary fission

  4. Encystation of trophozoites occurs in lower part of large intestine to become cysts

  5. Trophozoites and cysts passed out in feces

  6. Trophozoites can spread from intestine to liver, lung and brain through bloodstream by invading intestinal mucosa
• Intestinal amoebiasis (amoebic dysentery)

  • Incubation period: 1-4 weeks
  • Produces ulcerative lesions and bloody diarrhoea
• Extraintestinal amoebiasis


  • Happens when trophozoites enter deeper layers and carried to the liver through veins
  • Causes amoebic liver abscess containing pus that yields trophozoites
  • Trophozoites may enter other organs such as lungs, brain and skin
• Liver abscess contains fluid composed of leukocytes, bacteria, and cellular debris