NOTES

• Protozoa ("first animal") are unicellular eukaryotic organisms belonging to the new "Kingdom Protozoa"
• Protozoa are differentiated from prokaryotes by having organelles as subcellular structures, from algae by their lack of chlorophyll, from fungi by their lack of cell wall, and from slime molds by their inability to form fruiting bodies

  
• Protozoa are mostly microscopic in size
• Since their discovery by Leeuwenhoek (18th century), about 65000 have been described
• Protozoa are widely distributed and among the first links in the food chain
• Examples of protozoa


  • Causes of malaria in man
  • Coccidia
  • Amebas

  
• Cell membrane


  • Outer body covering; shape depends on material beneath called pellicle or periplast, consisting of either spirally arranged protein strips or thin layer of closely packed vesicles called alveoli; some are covered with hard plates called theca (in dinozoans)
• Nucleus


  • Two types: Vesicular nucleus (with endosome/karyosome or nucleoli) and Compact nucleus (micronucleus and macronucleus)
• Locomotory organelles


  • Flagellum, Cilium, Pseudopod
• Organelles associated with nutrition and excretion


  • Protozoa are chemoheterotrophs that ingest liquid (pinocytosis) or solid organic materials (phagocytosis); food is digested in food vacuoles; wastes are excreted by diffusion, exocytosis or through a permanent posterior opening called cytopyge; contractile vacuoles may be involved in osmoregulation
• Asexual (Clonal) reproduction


  1. Binary fission

  2. Multiple fission (Schizogony)

  3. Budding

  4. Plasmotomy
• Sexual reproduction


  1. Conjugation

  2. Syngamy
• Schizont or meront


  Dividing cell
• Merozoites or schizozoites


  Daughter cells
• Trophozoite


  Motile or vegetative stage of a protozoan

  
• Cyst


  Thick-walled stage formed by some protozoa
• Oocyst


  Cyst formed by coccidia
• Parasitic protozoa can cause physical damage to host tissue, deprive host of nutrients, and induce excessive immune response
• Modes of transmission of parasitic protozoa


  • Direct transmission of trophozoites
  • Fecal-oral transmission of cyst stages
  • Vector-borne transmission of trophozoites
  • Predator-prey transmission of zoites encysted in prey

  
• Amebas are unicellular eukaryotes that move mainly by means of pseudopodia
• Flagellates are unicellular eukaryotic organisms whose main locomotory organelle is 1 or more flagella
• The Apicomplexa are intracellular parasites characterized by the presence of cortical alveoli

  
• Ciliates are eukaryotes characterized by the presence of cilia on their cell membrane or portion of their surface

  
• Myxozoans are cnidarian animals that lost most of their multi-cellular characteristics as they adapted to endoparasitic life
• Microsporidians are spore-forming fungal parasites of invertebrates and vertebrates that lack motile structures
• Pneumocystis is a genus of yeast-like unusual fungus parasitic in the lungs of man and a variety of animals that lacks ergosterol in its plasma membrane

  
• Acanthamoeba


  • Trophozoites have two or three slender, hyaline projections (acanthopods) that taper to a finely rounded end; endosome is also large; trophozoites replicate by mitosis; cysts are uninucleate with a wall consisting of an endocyst positive for cellulose

  
• Balamuthia mandrillaris


  • Has trophozoite and cyst (uninucleate) stages that can be found in tissue; endosome is also large; trophozoites replicate by mitosis

  
• Acanthamoeba and Balamuthia infections are infrequent but appear to occur worldwide

  
• PAM


  Primary amoebic meningoencephalitis, presents with severe headache, fever, vomiting, focal neurologic deficits, progresses rapidly to coma and death
• GAE


  Granulomatous amoebic encephalitis, manifests as headaches, altered mental status, focal neurologic deficit, progresses over several weeks to death

  
• Pathogenic free-living amebas


  Belong to the Families Vahlkampfiidae, Acanthamoebidae and Balamuthiidae containing genera Naegleria, Acanthamoeba, and Balamuthia, respectively

  
• Naegleria fowleri


  • Has three stages - cysts, trophozoites, and flagellated forms
  • Trophozoites replicate by promitosis (nuclear membrane remains intact)
  • Nucleus has a large endosome
  • Contractile vacuole is conspicuous
  • Trophozoites can turn into temporary flagellated forms which usually revert back to the trophozoite stage
  • Cysts are uninucleate

  
• Naegleria fowleri is found in fresh water, soil, thermal discharges of power plants, heated swimming pools, hydrotherapy and medicinal pools, aquariums, and sewage
• Trophozoites of Naegleria fowleri


  Infect man or animals by entering the olfactory neuroepithelium and reaching the brain
• Acanthamoeba spp.


  • Relatively small amoebae without well developed ectoplasm
  • Have trophozoite and cyst stages
  • Occur in tissue

  
• Acanthamoeba spp. and Balamuthia mandrillaris are capable of causing granulomatous amebic encephalitis (GAE) and cutaneous forms in individuals with compromised immune systems

  
• Some Acanthamoeba spp. also cause keratitis and corneal ulcers
• Amphizoic amebas


  Capable of freeliving and parasitic existence
• Laboratory diagnosis of Naegleria infections


  1. Microscopic examination of cerebrospinal fluid (CSF): a wet mount may detect motile trophozoites, and a Giemsa-stained smear will show trophozoites with typical morphology

  2. Culture as in Acanthamoeba