2. CLASSIFICATION OF PARASITE

• Four medically important phyla of protozoa


  • Sarcomastigophora
  • Ciliophora
  • Apicomplexa
  • Microspora

  
• Two medically important phyla of helminths

  • Nemathelminthes (Class Nematoda)
  • Platyhelminthes (Class Cestoda & Class Trematoda)
• Types of parasites


  • Protozoa
  • Helminths
  • Ectoparasites

  
• Protozoa


  • Entamoeba
  • Giardia
  • Trichomonas
  • Plasmodium
  • Toxoplasma

  
• Helminths


  • Ascaris
  • Trichuris
  • Taenia
  • Echinococcus
  • Schistosoma
  • Fasciola
• Ectoparasites


  • Ticks
  • Fleas
  • Lice
  • Mites
• General Characteristics of Protozoa

  • Microscopic unicellular eukaryotes
  • Able to perform complex metabolic activities such as respiration, excretion and digestion
  • Most are free living; some are parasites

  
• Ectoplasm


  Outer, transparent layer; Functions: Protection, locomotion & sensation
• Endoplasm


  Inner, granular layer; Contains vacuoles & organelles (mitochondria, lysosomes, Golgi apparatus, etc); Functions: Nutrition & reproduction
• Most medically important protozoa are <50 μm.
• Karyosome


  A small mass of chromatin within the nuclear space; Located either at the centre (e.g. Plasmodium) or at the peripheral; May contain DNA (e.g. Plasmodium) or may not contain DNA (e.g. Trypanosomes)
• Most protozoa have a single nucleus; but each ciliate has two nuclei.
• Stages of Protozoa


  • Trophozoite stage: Active feeding and growing stage; Fed by phagocytosis or pinocytosis or through cytostomes
  • Cyst stage: A stage which is resistant to unfavourable condition; On excystation, it develops into trophozoites

  
• Monoxenous


  Complete their life cycle in one host
• Heteroxenous


  Complete their life cycle in more than one host
• Life cycle of protozoa

  1. Multiply asexually in trophic stage and transfer to others host by the cystic form

  2. Asexual reproduction ± man

  3. Sexual reproduction - mosquito

  
• Single host


  • Giardia lamblia
• Second host


  • Plasmodium spp.
• Reproduction of protozoa


  • Asexual: Binary fission, Schizogony
  • Sexual: Fusion of gametes to produce zygotes, Conjugation between two organisms
• Phyla of medically important protozoa

  • Ciliophora
  • Apicomplexa
  • Sarcomastigophora (Sarcodina, Mastigophora)
  • Microsporidia

  
• Pseudopodia


  Movement by protrusion of cytoplasm
• Amoebiasis


  Intestinal and extraintestinal infections caused by Entamoeba histolytica

  
• Entamoeba histolytica is the 3rd leading parasite cause of death in developing countries

  
• Entamoeba histolytica


  • A pathogenic amoeba, associated with intestinal and extraintestinal infections
  • Risk factors include consuming contaminated food or water, association with food handlers whose hands are contaminated

  
• Trophozoites are found in large intestine: lumen, mucosa, submucosa

  
• Life cycle of Entamoeba histolytica

  1. Cysts and trophozoites are passed in feces

  2. Infection occurs by ingestion of mature cysts in fecally contaminated food, water, or hands

  3. Excystation occurs in the small intestine and trophozoites are released, which migrate to the large intestine

  4. Trophozoites multiply by binary fission and produce cysts (encystation), and both stages are passed in the feces

  
• Cysts can survive days to weeks in the external environment and are responsible for transmission

  
• Trophozoites passed in the stool are rapidly destroyed once outside the body, and if ingested would not survive exposure to the gastric environment
• Kinetoplast


  Nucleation site for the growth of the axoneme microtubules
• Subphyla of Sarcomastigophora


  • Sarcodina (Amoeba)
  • Mastigophora (Flagellates)
• Sarcodina (Amoeba)


  • Most are free-living: Amoeba proteus, Acanthamoeba and Naegleria
  • Some are of medical importance: Entamoeba histolytica (Intestinal amoeba)
  • Movement by pseudopodia
  • Reproduction by binary fission

  
• Mastigophora (Flagellates)


  • Most are free-living: Euglena sp.
  • Some are of medical importance: Giardia lamblia (Intestinal flagellate), Leishmania (Tissue flagellate), Trypanosoma (Tissue flagellate)
  • Movement by flagella

  
• Kinetoplastida


  • Possess a kinetoplast: Leishmania (Tissue flagellate), Trypanosoma (Tissue flagellate)
  • Hemoflagellates: Systemic or local infection