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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
• How parasites cause disease

  Some parasites produce toxins or enzymes that may harm the host tissues, causing lytic necrosis. Some invasive and migratory parasites cause physical damage to tissues and organs. In some cases, the host immune response to the parasites causes more injury than do the parasites themselves.

  
• 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
• Anus


  The most common exit (through the feces) of parasites (roundworms - Ascaris)

  
• Urine


  May serve as exit for Trichomanas vaginalis, Strongyloides vermicularis. Schistosoma haematobium