Intro to parasitology

• Symbiosis

  Relationship where unlike microorganisms exist together
• Types of symbiotic relationships

  • Commensalism
  • Mutualism
  • Parasitism
• Commensalism


  Two species live together and one species benefits from the other without harming or benefiting the other
• Commensalism


  • Human body and most of the normal flora in the body
  • Whale shark with remora fish
• Mutualism


  Two organisms mutually benefit from each other
• Mutualism


  • Normal intestinal flora in the human body produces vitamin K (needed for clotting factors)
• Parasitism


  One party or symbiont (parasite) benefits to the detriment of the other (host)
• In most cases parasite deprives the host of essential nutrients and produce disease in the host
• Parasite


  One party or symbiont that benefits to the detriment of the other (host)
• Host


  The other party that is harmed by the parasite
• Classification of parasites based on habitat

  • Ectoparasites
  • Endoparasites
• Ectoparasites


  Live outside the host's body
• Ectoparasites

  • Fleas
  • Lice
• Infestation

  Invasion of the body by ectoparasites
• Endoparasites


  Live inside the body of the host
• Endoparasites


  • Helminths or worms
• Infection

  Invasion of the body by endoparasites
• Classification of parasites based on ability to live independently

  • Facultative parasites
  • Obligate parasites
• Facultative parasites


  Can live independently, do not have to live inside a host to complete their life cycle
• Facultative parasites


  • Free living
• Obligate parasites


  Must live inside the host to complete the life cycle
• Obligate parasites


  • Plasmodium
  • Leishmania
  • Hookworms
• Classification of parasites based on mode of living

  • Permanent parasites
  • Intermittent parasites
  • Incidental parasites
  • Transitory parasites
  • Erratic parasites
• Permanent parasites


  Remain in host from early life to maturity
• Permanent parasites

  • Plasmodium
• Intermittent parasites


  Simply visit the host during feeding time
• Intermittent parasites


  • Non-pathogenic parasites
  • Mosquitoes
  • Bedbugs
• Incidental parasites


  Occur in an unusual host
• Incidental parasites


  • Dog tapeworm in humans
  • Rat tapeworms
• Transitory parasites


  Larva develops in a host while the adult is free-living
• Transitory parasites

  • Echinococcus granulosus or dog tapeworm
• Erratic parasites

  Seen in an unusual organ, different from that which it ordinarily parasitizes
• Erratic parasites

  • Entamoeba histolytica in the liver or lung of humans
• Types of hosts

  • Definitive hosts
  • Intermediate hosts
  • Reservoir hosts
  • Paratenic hosts
• Definitive hosts


  Harbor the adult stage of the parasite or where the sexual stage or sexual phase of the life cycle of the parasite occur
• Intermediate hosts


  Harbor the larval stage of the parasite or where the asexual stage of the life cycle of the parasite occurs
• Intermediate hosts

  • Parasitic worm, Taena solium (pork tapeworm)
• Reservoir hosts

  Vertebrate hosts that harbor the parasite and may act as additional source of infection in man
• Reservoir hosts

  • Migratory birds serve as reservoir host for the parasite Capillaria philippinensis which people normally get from contaminated fresh water
• Paratenic hosts


  Serve as means of transport for the parasite (e.g. insect vectors) so that the infective stage of a certain parasite may reach its final host