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• Parasitology


  The scientific study of parasites

  
• Parasitism


  A symbiotic relationship that is of benefit to one party or symbiont (the parasite) and detrimental to the other party (the host)
• Parasite


  An organism that lives on or in a host organism, depending on the host for its nourishment
• Main classes of parasites that can cause disease in humans

  • Protozoa
  • Helminths
  • Ectoparasites

  
• Endoparasites


  Live inside of the host's body
• Ectoparasites


  Live on the outside of the host's body
• Infestation


  Invasion of the body by ectoparasites which are living outside the host's body (fleas, lice)

  
• Infection


  Invasion of the body by endoparasites; resulting from the entry and multiplication of the parasites within the host

  
• Classifications of parasites based on ability to live independently of the host

  • Facultative parasites
  • Obligate parasites

  
• Facultative parasites


  Organisms that can be parasitic, but do not have to live as parasites; they are capable of an independent life

  
• Obligate parasites


  Parasites that must live inside the host

  
• Classifications of parasites based on mode of living

  • Permanent parasites
  • Intermittent parasites
  • Incidental/accidental parasites
  • Transitory parasites
  • Erratic parasites

  
• Permanent parasites


  Parasites that remain in the host from early life to maturity

  
• Intermittent parasites


  Parasites that simply visit the host during feeding time

  
• Incidental/accidental parasites


  Parasites that occur in an unusual host

  
• Transitory parasites


  Parasites whose larva develop in a host, and adult forms are free-living

  
• Erratic parasites


  Parasites that are seen in an unusual organ, different from which they ordinarily invade

  
• Modes of transmission of parasites


  • Contact transmission
  • Ingestion of contaminated food and water
  • Fecal-oral transmission
  • Penetration of the skin from soil or contaminated water
  • Bite of blood-sucking insect vectors
  • Inhalation of eggs
  • Transplacental infection
  • Transmammary infection
  • Through sexual intercourse

  
• Contact transmission


  Direct contact with an infested person, through skin-to-skin, or through sexual transmission, or indirect contact with infected person's towel, bed sheets
• Ingestion of contaminated food and water

  The most common mode of transmission of intestinal parasites
• Fecal-oral transmission


  Ingestion of contaminated water/ food
• Penetration of the skin from soil or contaminated water

  Example: Hookworms, Strongyloides
• Bite of blood-sucking insect vectors


  Example: Plasmodium causing malaria; Dengue virus
• Inhalation of eggs


  Example: Pinworm (Enterobius vermicularis)
• Transplacental infection


  Example: Toxoplasma gondii
• Transmammary infection


  Example: Strongyloides, Ancylostoma
• Through sexual intercourse


  Example: Trichomanas vaginalis
• Lytic necrosis


  Some parasites produce toxins or enzymes that may harm the host tissues

  
• Traumatic damage


  Some invasive and migratory parasites cause physical damage to tissues and organs, destruction of individual cells, or occlusion of blood vessels and other tubular structures

  
• Host immune response


  In some cases, the host immune response to the parasites causes more injury than do the parasites themselves
• Types of immune response of humans to parasitic infections

  • Type 1: allergy or anaphylactic
  • Type 2: antibody-mediated
  • Type 3: immune complex
  • Type 4: cell-mediated
• Life cycle of a parasite

  The continuous sequence of changes undergone by that organism from one primary form to the development of the same form again

  
• Classification of hosts


  • Definitive host
  • Intermediate host
  • Reservoir hosts
  • Paratenic hosts
  • Accidental/ incidental host
  • Dead-end host
• Definitive host


  The host that harbors the adult or sexual stage of the parasite

  
• Intermediate host


  The host that harbors the larval or asexual stage of the parasite

  
• Reservoir hosts


  Vertebrate hosts that harbor the parasites and thus may act as additional source of infection in man
• Paratenic hosts


  Hosts that serve as transport for the parasites
• Accidental/ incidental host


  One that can serve as a host but is not the usual host in the parasite's life cycle
• Dead-end host


  A host that is unable to transmit the parasite to a different host, so that parasite cannot continue its life cycle

  
• Ports of exit of parasites

  • Anus
  • Urine
  • Sputum
  • Vaginal discharge