INTRO TO UNICELLULAR PARASITES

• Protozoa

  "first animal"
• Protozoa

  • Unicellular eukaryotes
  • Differentiated from prokaryotes by having organelles as subcellular structures
  • Differentiated from algae by their lack of chlorophyll
  • Differentiated from fungi by their lack of cell wall
  • Differentiated from slime molds by their inability to form fruiting bodies
• Anton Van Leeuwenhoek's discovery of the first species, Amoeba proteus, in the early 1700s, he first called them "animalcules"
• Classification of living organisms

  • SK Prokaryota
  • K Archaea
  • K Bacteria
  • SK Eukaryota
  • K Protozoa
  • K Chromista
  • K Fungi
  • K Plantae
  • K Animalia
• Protozoa


  • Classified either under Kingdom Protista or as forming a separate kingdom - Kingdom Protozoa
  • Ciliates, apicomplexans, and dinoflagellates under K Chromista
  • Myxozoans under K Animalia
• Cell membrane

  A pellicle or periplast occurs beneath it
• Vesicular nucleus

  • With a "visible" more or less central body
  • Endosome in trypanosomes, parasitic amebas and phytoflagellates
  • Nucleolus in the Apicomplexa and dinoflagellates

  
• Compact nucleus

  • In ciliates
  • Micronucleus - small, diploid, apparently controls reproductive functions
  • Macronucleus - large, polyploid, center of cellular control and regulation
• Locomotory organelles


  • Flagellum - a central axoneme and outer sheath; at base kinetosome (basal body, blepharoplast)
  • Cilium or cilia - may have tactile function; may fuse to form cirrus, membranelle or undulating membrane
  • Pseudopod - temporary organelle
  • Some protozoans have no readily visible locomotory organelle - move by gliding smoothly along without change in shape, in Toxoplasma, Sarcocystis, and coccidian sporozoites and merozoites
• Chemoheterotrophs


  Protozoans are mostly chemoheterotrophs
• Food acquisition

  • By phagocytosis (e.g. amebas) or by a permanent one such as cytostome (e.g. ciliates) or micropore (e.g. Apicomplexan merozoites)
  • Pinocytosis - ingesting fluid food through small, temporary openings in the body wall
• Waste excretion


  • By diffusion through the body wall
  • By exocytosis (transported out of the cell when food vacuoles come in contact with the cell membrane)
  • Through a permanent posterior opening called cytopyge
  • Contractile vacuole - for osmoregulation
• Types of asexual reproduction

  • Binary fission - most common, divide completely into 2 daughter cells
  • Multiple fission (Schizogony/Merogony) - the nucleus divides several times before the cytoplasm (in the Apicomplexa)
  • Budding - a small daughter, which grows to full size later, separates from the side of a parent cell; in Babesia spp.
  • Endodyogeny - internal budding resulting in 2 daughter cells
  • Endopolygeny - internal budding resulting in more than 2 daughter cells
  • Ectopolygeny - external budding resulting in more than 2 daughter cells
  • Plasmotomy - special form of binary fission in which a multinucleate organism divides into smaller multinucleate daughter individuals by cytoplasmic division but without mitosis followed by karyokinesis of the daughter cells, e.g. Opalina
• Types of sexual reproduction

  • Conjugation - 2 individuals come together temporarily and fused partly, macronuclei degenerate, micronuclei divide several times, exchange of one of their resultant haploid pronuclei (in ciliates)
  • Syngamy - 2 gametes fuse, zygote may either divide to form sporozoites (sporogony or sporulation), or not
• Gamogony/Gametogony


  Formation of gametes
• Sporogony or sporulation


  Formation of sporozoites
• Cysts (or oocysts in coccidia)


  May be formed by some protozoa where a thick wall is produced by the protozoa around itself
• Trophozoite


  Refer to the motile or vegetative stage of a protozoa; may have special names

  
• General effects of parasitic protozoa/unicellular parasites

  • Absorb nutrients e.g. glucose by trypanosomes
  • Interfere with absorption of food e.g. Giardia, Cryptosporidium
  • Produce toxin e.g. sarcocystin by Sarcocystis
  • Destroy tissues or cells e.g. coccidia, blood parasites
  • Stimulate or interfere with host immune system (e.g. depressed immune response of hosts infected with Trypanosoma evansi)
• Premunity (premunition)


  Stimulation of immunity by low grade infection, e.g. in Babesia spp. infections
• Groups of pathogenic protozoans

  • Amebas
  • Flagellates
  • Coccidia and related species
  • Ciliates
  • Microspora-Myxozoa
  • Unclassified
• Modes of transmission of unicellular parasites