MICP Introduction to Parasitology

• Parasitology

  The study of large parasites
• Parasite

  Organism that depends on the host for survival
• Host

  Organisms that harbor the parasite and provide its nourishment
• Vector

  A living organism that carries a disease-causing organism to new hosts
• Vectors

  • Mosquitoes
  • Fleas
  • Lice
  • Sandflies
  • Ticks
• Facultative parasite


  Parasites that can live independently of the host (i.e., free living)
• Obligate parasite

  Parasites that must live inside a host
• Majority of the parasites that infect humans are obligate parasites
• Symbiosis

  A relationship where unlike organisms exist together
• Mutualism

  A symbiotic relationship in which two organisms mutually benefit from each other
• Parasitism

  A symbiotic relationship where one party or symbiont (i.e., the parasite) benefits to the detriment of the (the host)
• Commensalism

  A form of symbiotic relationship in which two species live together and one species benefits from the other without harming or benefitting the other
• Ectoparasites

  Those that live outside of host body
• Endoparasites


  Lives inside the body of host
• Infestation

  Invasion of the body by ectoparasites
• Infection

  Invasion of the body by endoparasites
• Permanent parasite


  Parasites that remain in a host from early life to maturity
• Intermittent parasite


  Parasites that simply visit the host during feeding time
• Incidental parasite


  Parasites that occur in an unusual host
• Transitory parasite


  Parasites whose larva develops in a host while the adult is free-living
• Erratic parasite


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


  Hosts that harbor the adult stage of the parasite
• Intermediate host


  A host that harbors the larval stage of the parasite
• Aberrant host


  One in which the parasite cannot complete its development or the appropriate phase of its development
• Reservoir host


  Vertebrate host that harbor the parasite and may act as an additional source of infection in man
• Paratenic host


  Serve as means of transport for the parasitic larva
• Sources of Exposure to Infection or Infestation

  • Contaminated Soil and Water
  • Food containing the Parasite's Infective Stage
  • A Blood Sucking Insect
  • A Domestic or wild Animal harboring the Parasite
  • Another Person and Fomites
  • Auto-Infection/One's self
• Mode of Transmission


  • Ingestion
  • Contaminated Water
  • Contaminated Food
  • From eating food containing mature larval stage
  • Enter body from soil via skin
  • Sexual intercourse
• Portal of Exit


  A path for the microorganism to escape from the host
• The most common portal of exit of parasites is through the anus
• Other portals of exit

  • Urine
  • Sputum
  • Vaginal discharge
• Pathogenesis


  The dynamics of any disease process
• Traumatic/Physical Damage


  Manifestations may be due to the direct physical damage caused by the parasite in the organ it parasitizes or at the point of entry of the parasite
• Lytic Necrosis


  Enzymes and other substances produced by many parasites that are necessary for them to digest food available in the immediate environment may cause harm to the host tissues
• Stimulation of Host Tissue Reaction


  Process by which a host interacts with and responds to parasites that it encounters
• Toxic and Allergic Phenomena

  Hemolysis and hypersensitivity reaction
• Opening of Pathways for entry of Other Pathogens into the Tissues


  The presence of the parasites and the damage they produce to the tissues may favor the entry and proliferation of other organisms, especially bacteria