PATHOGENIC AMOEBAS

• Pathogenic amebas


  Traditionally under Subphylum Sarcodina, presently either under Amoebozoa or Archamoebae, move by pseudopodia, also used for ingesting food, cytoplasm divided into ectoplasm and endoplasm

  
• Pathogenic amebas


  • Mostly holozoic, usually reproduce by asexual binary fission or rarely, by multiple fission, by budding or by plasmotomy, most species have trophozoite and cyst forms
• Two groups of pathogenic amebas

  • Freeliving species
  • Parasitic species
• Freeliving species


  • Family Vahlkampfiidae
  • Family Acanthamoebidae
  • Family Balamuthiidae
• Parasitic species


  • Family Endamoebidae
• Entamoeba histolytica


  Man, mammals
• Naegleria fowleri is regarded as flagellate in some new references, hence the disease caused (primary amebic meningoencephalitis) is a misnomer

  
• Pathogenic freeliving amebas


  • Naegleria fowleri
  • Acanthamoeba spp.
  • Balamuthia mandrillaris

  
• Primary Amebic Meningoencephalitis (PAM)

  Acute, and usually lethal, central nervous system (CNS) disease caused by Naegleria fowleri

  
• Acanthamoeba keratitis


  Opportunistic pathogen, e.g. HIV patients
• Acanthamoeba granulomatous encephalitis (AGE)


  Opportunistic pathogen, e.g. HIV patients

  
• Acanthamoeba cutaneous form


  Opportunistic pathogen, e.g. HIV patients
• Balamuthia Granulomatous Encephalitis (BGE) or meningoencephalitis


  Also as opportunistic pathogen

  
• Balamuthia cutaneous form


  Also as opportunistic pathogen
• Life cycle and transmission of N. fowleri and other species of amphizoic amebas

  Stages or forms (all have uninucleate cysts and large endosome)

  
• Worldwide Distribution of Reported Primary Amebic Meningoencephalitis (PAM) cases

  
• Naegleria fowleri


  Destroys nerve and other mammalian cells by piecemeal ingestion, a process termed trogocytosis, virulence factors: phospholipase A and C, proteases, sphingomyelinase and lysophospholipase, host of Legionella pneumophila - agent of Legionnaire's disease

  
• Acanthamoeba species identified in human tissues

  • A. culbertsoni, A. polyphaga, A. hatchetti, A. castellanii, A. rhysodes

  
• Acanthamoeba Group II


  Thick ectocyst and polygonal endocyst
• Acanthamoeba Group III


  Thin ectocyst adjacent to the endocyst
• Acanthamoeba trophozoites have characteristic acanthapodia, contractile vacuole and prominent nucleus

  
• Balamuthia mandrillaris


  Cases in man, primates (mandrill, gorillas, baboons, gibbons, monkeys), and domestic animals (horses, sheep, dogs), similarities with Acanthamoeba, differences: larger trophozoites and cysts, Acanthamoeba can cause amebic keratitis mostly in contact-lens users, encephalitis in almost exclusively in immunocompromised persons, Acanthamoeba is the hardier organism, Balamuthia grows only in cell-free axenic or cell culture media without Escherichia coli, one strain has been found to be a host also of L. pneumophila

  
• Entamoeba histolytica


  Causes invasive intestinal and extraintestinal amebiasis, Entamoeba dispar refers to the non-pathogenic intestinal commensal organism that is visually indistinguishable from E. histolytica

  
• Hosts of Entamoeba histolytica

  • Man, orangutan, gorilla, chimpanzee, gibbons, langurs, many species of macaques, baboons, guenons, spider and other monkeys, dog, cat, pig, rat, mouse, guinea pig, rabbit, possibly cattle
• Location of Entamoeba histolytica

  Large intestine, sometimes liver, occasionally lungs, and rarely other organs including brain and spleen

  
• Entamoeba histolytica trophozoites


  20-30 μm in diameter, has clear layer of ectoplasm and granular endoplasm

  
• Entamoeba histolytica cysts


  10-20 μm in diameter, 4 nuclei when mature, often contain rod-like chromatoid bodies, young cysts have diffused glycogen

  
• Entamoeba histolytica needs to be differentiated from commensal species
• Amebic liver abscess is probably 5–50x less common than that of diarrhea
• An estimated 40,000 – 100,000 annual deaths from amebiasis, 2nd to malaria as a cause of death resulting from a protozoan parasite

  
• Prevalence and geographic distribution of Entamoeba in humans, as determined by molecular methods

  
• Pathogenesis of Entamoeba histolytica infection

  Adherence to the colonic mucus and epithelial layers and disruption of mucus layer, Interaction of a D-gal- or GalNAc- (D-galactose- or N- acetyl-D-galactosamine-) lectin adhesin with host- derived glycoconjugates apoptosis of enterocytes, Tissue invasion, Spread through the bloodstream (hematogenously) and establishment of persistent extra-intestinal infections (most commonly amebic liver abscess)

  
• Syndromes of Entamoeba histolytica infection

  • Asymptomatic
  • Amebic colitis (amebic dysentery)
  • Amebic liver abscess (anchovy sauce) - most common extra-intestinal amebiasis; 10% of amebic colitis cases

  
• Toxic megacolon


  Most feared complication of amebic colitis
• Ameboma


  Mimics carcinoma of the colon
• Entamoeba invadens


  Parasite of reptiles of wide distribution, forms trophozoites (15 to 20 mm) and cysts (produced even in vitro, a unique feature of this species), mature cysts - quadrinucleate, invades primarily the rectal, the rapid regenerative ability of the mucosa results in the formation of lamellar, necrotic layers that can plug the intestinal lumen in extreme cases, if liver is affected, lesions consist of abscesses, causes high losses among reptiles, can be fatal in snakes within 3 weeks
• Entamoeba ranarum


  Closely similar to E. histolytica, in gut and liver of tadpoles, has been reported in a python

  
• Entamoeba muris


  In mice and rats
• Entamoeba moshkovskii and E. polecki

  Morphologically similar to E. histolytica, have been associated with intestinal disease in man in recent years

  
• Traditionally under Subphylum Sarcodina, presently either under Amoebozoa or Archamoebae, move by pseudopodia, also used for ingesting food, cytoplasm divided into ectoplasm and endoplasm

  Pathogenic amoeba