Parasites

• Parasite:

  A parasite may be unicellular (protozoa) or multicellular organism (worms) which exploits its host for the purpose of staying alive

  • The parasite offers nothing to the relationship, creating an arrangement which may be neutral or harmful, but never positive

  • Some parasitic relationships are harmless, while in other cases a parasite can damage or kill its host
• 2 main groups of medically important parasites:

  • PROTOZOA (systemic / gastrointestinal)
  • HELMINTHS (worms) (systemic / gastrointestinal)
• PROTOZOA:

  (A) Active (TROPHOZOITE); causes disease

  (B) Infective (CYST); resistant, transmissible form, survives for extended periods in the environment
• ❖ HELMINTHS (worms):

  (A) Active (WORM and LARVAE); causes disease

  (B) Infective (EGGS); resistant, transmissible form, survives for extended periods in the environment
• DEFINITIVE HOST: supports the sexually mature, reproducing adult parasite

  INTERMEDIATE HOST: supports the immature or non-reproductive forms of a parasite.

  • Some parasites (e.g. protozoa) utilise a definitive host only whilst others (e.g. worms) may utilise one (or more) intermediate hosts before maturing in its definitive host
• Types of parasites:

  
• Protozoa:

  • Unicellular
  • Eukaryotic (membrane bound organelles)
  • Asexual reproduction (mainly): produces daughter cells with DNA identical to parent protozoan
  • Size: varies 10–150 µm (visualised by light microscopy)
  • Many form ‘dormant, resistant’ stages: cysts (consumed by host)
  • Classified according to their locomotive apparatus
• Protozoa:

  • Unicellular
  • Eukaryotic (membrane bound organelles)
  • Asexual reproduction (mainly): produces daughter cells with DNA identical to parent protozoan
  • Size: varies 10–150 µm (visualised by light microscopy)
  • Many form ‘dormant, resistant’ stages: cysts (consumed by host)
  • Classified according to their locomotive apparatus
• Classification of protozoa's:

  1. Amoeba
  2. ciliates
  3. flagellates
  4. apicomplexans

  obtain nutrition through ; engulfing, cytosome, pinocytosis
• Entamoeba histolytica:

  Gastrointestinal symptoms: Ulceration of colonic epithelium, amoebic dysentery, amoebic abscess in vital organs.

  
• Balantidium coli:

  Largest protozoan parasite of humans and the only ciliate which is pathogenic to humans

  cyst: ineffective

  trophozoite: causes infection
• Gardia Intestinalis: