Introduction to Parasitology

• Symbiosis


  Living together, association of 2 living organisms, each of different species
• Types of symbiotic relationships


  • Commensalism
  • Mutualism
  • Parasitism
• Commensalism


  Association: beneficial to one, neutral to other
• Mutualism

  Association: beneficial to both
• Parasitism


  Association: beneficial to one, detrimental to other
• Classification of parasites based on habitat


  • Ectoparasites
  • Endoparasites
• Ectoparasites


  Parasites that live outside the host's body
• Infestation


  Invasion of body by ectoparasites
• Endoparasites

  Parasites that live inside the body of the host
• Infection

  Invasion and multiplication of endoparasites within the body
• Ectoparasites

  • Fleas, lice
• Endoparasites

  • Helminths or worms
• Classification of parasites based on ability to live independently

  • Facultative parasites
  • Obligate parasites
• Facultative parasites

  Parasites that can live independently of the host
• Obligate parasites

  Parasites that must live inside a host
• Facultative parasites

  • Free-living nematodes
• Obligate parasites

  • Plasmodium, Leishmania, hookworms
• Classification of parasites based on mode of living in host

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

  Parasites that remain from early life to maturity
• Permanent parasites

  • Plasmodium
• Intermittent parasites

  Parasites that simply visit host during feeding time
• Intermittent parasites

  • Non-pathogenic parasites
• Incidental parasites

  Parasites that occur in an unusual host
• Incidental parasites

  • Dog tapeworm in humans
• Transitory parasites

  Parasites whose larva develop in a host while the adult is free-living
• Transitory parasites

  • Echinococcus granulosus (dog tapeworm)
• Erratic parasites

  Parasites that are seen in an unusual organ, different from that which ordinarily parasitizes
• Erratic parasites

  • Ascaris lumbricoides in lungs or kidneys
• Definitive hosts

  Hosts that harbor the adult stage of the parasite or where the sexual stage of the life cycle occurs
• Definitive hosts

  • Humans for the intestinal worm Ascaris, mosquito for the malaria parasite Plasmodium
• Intermediate hosts

  Hosts that harbor the larval stage of the parasite or where the asexual stage of the life cycle occurs
• Intermediate hosts

  • Cow for the beef tapeworm Taenia saginata, humans for the malaria parasite Plasmodium
• Reservoir hosts

  Vertebrate hosts that harbor the parasite and may act as an additional source of infection for humans
• Reservoir hosts

  • Migratory birds for the parasite Capillaria philippinensis
• Paratenic hosts

  Hosts that serve as a means of transport for the infective stage of a parasite to reach its final host
• Paratenic hosts

  • Insect vectors
• Sources of exposure to parasitic infections

  • Contaminated soil or water
  • Food containing parasite's infective stage
  • Blood-sucking insect
  • Domestic or wild animal harboring parasite
  • Another person and their environment
  • One's self (auto-infection)
• Contaminated soil or water

  Most common source of exposure for most parasitic worms or helminths
• Parasites from contaminated soil or water

  • Ascaris lumbricoides, Trichuris trichiura, Strongyloides stercoralis, human hookworms, parasitic amoeba and intestinal flagellates, blood fluke larvae, Taenia solium eggs
• Food containing parasite's infective stage

  Source of infection for fish tapeworm, intestinal and liver flukes, Trichinella spiralis, Taenia solium, Taenia saginata