Amoeba

• Protozoans


  single - celled eukaryotic microorganisms belonging to kingdom Protista
• Protozoa


  Morphology: UNICELLULAR; a single "cell-like unit"
• Metazoa 


  Morphology: MULTICELLULAR: a number of cells, making up a complex individual
• Protozoa


  Physiology: a single cell performs all the functions; (reproduction, digestion, respiration, excretion, etc.)
• Metazoa 


  Physiology: each special cell performs a particular functions
• Protozoa 


  Example: Ameba
• Metazoa 


  Example: Tapeworm
• Protozoans


  Single-celled eukaryotic microorganisms belonging to kingdom Protista
• Protozoan cell


  • Performs all functions
  • Most are completely non-pathogenic but few cause major diseases (i.e. malaria, leishmaniasis, sleeping sickness)
  • Differentiated to metazoa

  
• Protozoa


  Metazoa
• Morphology of protozoa


  Unicellular; a single "cell-like unit"

  
• Morphology of metazoa


  Multicellular; a number of cells, making up a complex individual
• Physiology of protozoa


  A single cell performs all the functions: reproduction, digestion, respiration, excretion, etc.
• Physiology of metazoa


  Each special cell performs a particular function
• Protozoa


  • Ameba
• Metazoa


  • Tapeworm

  
• Chromatoid body


  Extranuclear chromatin material (i.e. E. histolytica cyst)
• Karyosome


  DNA containing body, situated peripherally or centrally within the nucleus
• Kinetoplast


  Non nuclear DNA present in addition to nucleus. Seen in trypanosomes. Flagellates originates near the kinetoplast. Point of origin of flagellum is called as basal body

  
• Entamoeba


  • Vesicular nucleus
  • Centrally (or near) central located small karyosome/ karyosomal chromatin
  • Varying numbers of chromatic granules adhering to the nuclear membrane

  
• Taxonomic classification of Entamoeba

  • Subphylum: Sarcodina
  • Superclass: Rhizopoda
  • Class: Lobosea
  • Order: Amoebida
  • Family: Entamoebidae
  • Genus: Entamoeba

  
• Entamoeba histolytica, E. dispar, E. moshkovskii


  Morphologically identical; same size
• Differentiation of Entamoeba species

  By isoenzyme analysis PCR restriction fragment length polymorphism and typing monoclonal antibodies

  
• Entamoeba hartmanni


  "Small race" of E. histolytica, differentiated primarily on the basis of size
• Entamoeba histolytica


  • Pseudopod-forming non-flagellated protozoan parasite
  • Most invasive
  • Only member of the family to cause colitis and liver abscess
  • Life cycle – 2 stages (cyst, trophozoite)
  • Host: humans

  
• Mode of transmission of Entamoeba histolytica


  • Ingested cysts from fecally-contaminated material
  • Venereal transmission through fecal-oral contact
  • Direct colonic inoculation through contaminated enema equipment

  
• Entamoeba histolytica


  • Eukaryotic organisms BUT there is lack of organelles, lack of glutathione metabolism, Use of pyrophosphate instead of ATP at several steps in glycolysis, Inability to synthesize purine nucleotides de novo, Nuclear encoded mitochondrial genes i.e. pyridine nucleotide transhydrogenase and hsp60 are present

  
• Trophozoites


  • Highly motile
  • Possess pseudopodia
  • Characteristic progressive and directional movement, with pseudopodia as locomotory organelles
  • Ingested RBCs are observed as pale, greenish, refractile bodies in the cytoplasm of amoeba
  • Ability to colonize and/or invade the large bowel
  • Mutiply by binary fission

  
• Cysts


  • Spherical
  • Highly refractile hyaline cyst wall
  • One to four nuclei
  • Rod-shaped (or cigar-shaped) chromatoidal bars
  • Never found within invaded tissues
  • Cysts are typically found in formed stool, whereas trophozoites are typically found in diarrheal stool
  • Excystation occurs in the small intestine and trophozoites are released, which migrate to the large intestine
  • Trophozoites multiply by binary fission and produce cysts , and both stages are passed in the feces
  • Trophozoites passed in the stool are rapidly destroyed once outside the body, and if ingested would not survive exposure to the gastric environment

  
• Pathogenesis of Entamoeba histolytica

  • Production of enzymes or other cytotoxic substances
  • Contact-dependent cell killing
  • Cytophagocytosis

  
• Pathogenesis of Entamoeba histolytica

  • Trophozoites adhere to colonic mucosa through a galactose-inhibitable adherence lectin (Gal lectin) → kills mucosal cells by activation of caspase-3 → apoptotic death engulfment

  
• Asymptomatic Entamoeba histolytica infection

  Majority of cases are ASYMPTOMATIC (cyst being passed out in the stools – cyst carrier state)

  
• Clinical manifestations of Entamoeba histolytica infection

  • Amebic colitis
  • Ameboma
  • Amebic liver abscess (ALA)
  • Secondary Amebic Meningoencephalitis (SAM)
• Amebic colitis


  • Gradual onset of abdominal pain and diarrhea w/ or w/out blood and mucus on stools
  • Children may develop fulminant colitis with severe bloody diarrhea, fever, abdominal pain
  • Most serious complication: perforation and secondary bacterial peritonitis
• Ameboma


  • Mass-like lesion with abdominal pain and history of dysentery
  • Mistaken for carcinoma
  • Asymptomatic ameboma may also occur

  
• Amebic liver abscess (ALA)


  • Most common extra-intestinal form of amebiasis
  • Cardinal manifestations: fever, right upper quadrant pain (pain either localized in or referred to right shoulder)
  • Most serious complication: rupture into the pericardium, rupture into the pleura, and super infection
  • 2nd most complication: Intraperitoneal rupture
• Secondary Amebic Meningoencephalitis (SAM)


  • Occurs in 1-2 %
  • Amebiasis + altered mental status
• Differential diagnosis of acute amebic colitis

  • Bacillary dysentery (Shigella, Salmonella, Campylobacter, Yersinia, enteroinvasive E. coli)

  
• Differential diagnosis of amebic liver abscess


  • Pyogenic liver abscess
  • TB of the liver
  • Hepatic carcinoma
• Differential diagnosis of genital amebiasis


  • Carcinoma
  • TB
  • Chancroid
  • Lymphogranuloma venereum