Parasitology: Protozoa part 1

• Organisms from the phylum Sarcomastigophora, are amoeboid and flagellated parasites classified under the Kingdom Protozoa known to cause infections in humans
• Amoebae


  Classified under the subphylum Sarcodina, characterized by the presence of foot-like projections in the cytoplasm known as pseudopodia
• Flagellates


  Classified under the subphylum Mastigophora, characterized by the presence of whip-like flagella
• Subphylum Sarcodina: Pathogenic and non-pathogenic amoeba


  • Entamoeba
  • Naegleria
  • Acanthamoeba
• Amoeba subtypes


  • Intestinal
  • Commensals
  • Free living
• Entamoeba


  Frequently affecting invertebrate and vertebrate organisms, characterized by a vesicular nucleus with a comparatively small karyosome located at or near its center and with varying characteristics of the peripheral chromatin attached to the nuclear membrane
• E. histolytica, E. dispar, and E. moshkovskii are morphologically similar and can only be differentiated by isoenzyme analysis, restriction fragment length polymorphism, typing with monoclonal antibodies, and polymerase chain reaction
• E. hartmanni is considered to be the "small race" of E. histolytica because of its small size
• Intestinal Species


  • E. histolytica
  • E. hartmanni
  • E. coli
  • I. butschlii
  • E. moshkovskii
  • E. polecki
  • E. chatton
  • E. gingivalis
• Extraintestinal Species


  • Naegleria fowleri
  • Acanthamoeba species
• Amoeba


  • Locomotion: pseudopods (they extend their cytoplasm, false feet)
  • Morphologic forms: trophozoite and cysts (except E. gingivalis, Dientamoeba fragilis is an intestinal flagellate)
  • Most inhabit the large intestine EXCEPT: Entamoeba gingivalis
  • All are commensals EXCEPT: Entamoeba histolytica
• Excystation


  1. Cyst to trophozoite

  2. Site: ileocecal area of intestine
• Encystation


  1. Trophozoite to cyst

  2. Site: intestinal tract only

  3. Happens due to: amoeba overpopulation, pH change, change in food supply, oxygen availability
• Genus Entamoeba


  True amoeba: presence or peripheral chromatin and visible nuclear membrane (both cyst and trophozoite) and chromatoidal bodies (in cyst only)
• Genus Endolimax and Iodamoeba


  No peripheral chromatin and chromatoidal bodies
• Chromatoidal bars


  Condensed RNA material
• Karyosome / Karyosomal chromatin


  Central mass of chromatin (karyosome found in the center of nucleus)
• Peripheral chromatin


  Chromatin surrounding the karyosome
• Glycogen mass


  Stores food especially on young cysts
• Laboratory diagnosis


  • Saline wet preparation: show the motility of amebic trophozoites
  • Iodine wet preparation: Internal cytoplasmic and nuclear structures
  • Permanent smear: Confirms parasite identification because it accurately distinguishes the identifying characteristics of the protozoa
• General Characteristics of Amoebic Trophozoites and Cyst


  • Trophozoite: Motile, feeding stage, delicate and fragile, found in soft, liquid and loose consistency, destroyed by iodine
  • Cyst: Non-motile, non-feeding stage, has a protective cell wall against harmful environment, found in formed stool
• Trophozoite replicates via asexual binary fission
• Cyst is the infective stage
• Entamoeba histolytica


  Tissue invading intestinal amoeba
• Stages of Entamoeba histolytica


  • Cyst (infective stage)
  • Trophozoite (extraintestinal sites)
• Diseases caused by Entamoeba histolytica


  • Asymptomatic/Carrier
  • Intestinal amebiasis: Amebic colitis/dysentery
  • Extraintestinal amebiasis: Hepatic amebiasis or amoebic liver abscess (ALA) or amebic hepatitis, Visceral amebiasis (lungs, spleen, brain)
• Diagnosis of Entamoeba histolytica


  • Stool exam: Cyst has quadrinucleated, with cigar-shaped chromatoidal body, Trophozoite has minute, central, bull's eye karyosome, progressive, unidirectional motility (long, fingerlike pseudopodia), with INGESTED RBCs (pathognomonic)
• Treatment of Entamoeba histolytica


  • Mild, moderate, severe intestinal disease: METRONIDAZOLE
  • Asymptomatic cyst passers: DILOXANIDE FUROATE, Iodoquinol or paromomycin
  • ALA: metronidazole, percutaneous drainage for prompt symptom relief
• Entamoeba coli has 8 nuclei, Entamoeba histolytica has 4 nuclei
• Round- based, wide necked intestinal ulcers are caused by Balantidium coli, Flask-shaped ulcers are caused by Entamoeba histolytica
• Entamoeba histolytica can invade the liver and brain
• Differences between Entamoeba histolytica and Entamoeba coli


  • Trophozoite: Motility/Movement, Pseudopods, Endoplasm, Nucleus
  • Entamoeba histolytica: Moves in one direction, finger-like hyaline pseudopods, endoplasm contains RBC but no bacteria or cell detritus, nucleus not visible when stained
  • Entamoeba coli: Moves in several directions, blunt and round pseudopods, endoplasm contain bacteria, yeasts, and cell detritus/debris, stained nucleus consists of thicker nuclear membrane with layer of variously sized chromatin granules
• Balantidium coli


  Causes ragged intestinal ulcers
• Entamoeba histolytica


  Causes flask-shaped ulcers
• Entamoeba histolytica


  • Can invade the liver, brain
• Trophozoite characteristics


  • Motility/Movement
  • Pseudopods
  • Endoplasm
  • Nucleus
  • Karyosome
• Cyst characteristics


  • Shape
  • Karyosome
  • No. of Matured Cyst
• Entamoeba histolytica


  Intestinal amebiasis, Amebic colitis, Amebic dysentery, Extraintestinal amebiasis
• Entamoeba coli


  Non pathogen, closely resembles E. histolytica
• Differentiation between E. histolytica and E. dispar is NOT POSSIBLE by microscopy. This can only be done by PCR, enzyme-linked immunosorbent assay (ELISA), and isoenzyme analysis.