Chapter 8 (intro to para)

• Symbiosis


  Relationship where unlike microorganisms exist together
• Three types of symbiotic relationship


  • Commensalism
  • Mutualism
  • Parasitism
• Commensalism


  Form of symbiotic relationship in which two species live together and one species benefits from the other without harming or benefiting the other
• Commensalism


  • Human body and most body's normal flora
• Mutualism


  Symbiotic relationship in which two organisms mutually benefit from each other
• Mutualism


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


  Form of symbiotic relationship where one party or symbiont (i.e parasite) benefits to the detriment of the other (the host)
• In most cases the parasite deprives the host of essential nutrients and produce disease in the host
• Parasitism


  • Malnutrition caused by intestinal parasites
• Elements of parasitism


  • Parasite
  • Host
• Ectoparasites


  Parasites that live outside the host's body
• Infestation


  Invasion of the body by ectoparasites
• Endoparasites


  Parasites that live inside the body of the host
• Infection


  Invasion of the body by endoparasites
• Endoparasites


  • Helminths or worms
• Facultative parasites


  Parasites that can live independently of the host (i.e. free living), do not have to live inside a host to complete their life cycle
• Facultative parasites


  • Strongyloides stercoralis
• Obligate parasites


  Parasites that must live inside a host to complete the life cycle, majority of the parasites that infect humans are obligate parasites
• Obligate parasites


  • Plasmodium, Leishmania, hookworms
• Permanent parasites


  Parasites that remain in a host from early life to maturity
• Permanent parasites


  • Plasmodium
• Intermittent parasites


  Parasites that simply visit the 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 develops in a host while the adult is free-living
• Transitory parasites


  • Echinococcus granulosus or dog tapeworm
• Erratic parasites


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


  • Entamoeba histolytica in human liver or lung
• Definitive hosts


  Harbor the adult stage of the parasite or where the sexual stage or phase of life cycle of 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, Taenia 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 the 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 so that the infective stage of a certain parasite may reach its final host, organism that harbors the sexually immature parasite but is not necessary for the parasite's development cycle to progress
• Paratenic hosts


  • Insect vectors
• Sources of exposure to infection or infestation

  • Contaminated soil or water
  • Food containing the parasites infective stage
  • Blood-sucking insect
  • Domestic or wild animal harboring the parasite
  • Another person and his or her clothing, bedding, or the immediate environment he or she has contaminated
  • One's self (auto-infection)
• The most common source of exposure to infection is soil contaminated or polluted with human feces
• Modes of transmission


  • Fecal-oral transmission or Ingestion of contaminated food and water
  • Penetration of the skin from the soil or contaminated water
  • Bite of blood-sucking insect vectors
  • Inhalation of eggs
  • Transplacental or congenital infection
  • Transmammary (mother's milk) infection
  • Sexual intercourse
• Portals of exit of parasites

  • Anus
  • Urine
  • Sputum