Parasitology

• Parasitology


  Area of biology concerned with the phenomenon of dependence of one living organism on another
• Parasites


  Organisms that live for their survival at the expense of the host
• Classification of parasites

  • Habitat
  • Mode of living
  • Duration of infection/infestation
  • Pathogenicity

  
• Endoparasite


  • A parasite which lives within the body of the host
  • Infection is the term that denotes the presence of an endoparasite

  
• Ectoparasite


  • Those outside the body of the host; those on body surfaces like skin, surface i.e. lice
  • The presence of an ectoparasite will cause an infestation

  
• Obligate parasite


  • Need a host to complete their development
  • Example: Taenia solium
• Facultative parasite


  • May exist in a free-living state. May become parasitic when the need arises
  • Example: Some fungi and bacteria

  
• Accidental/Incidental parasite


  • Parasite that established itself in a host where it does not ordinarily live
  • Example: Echinococcus granulosus

  
• Erratic parasite


  • Parasite found in an organ which is not its usual habitat
  • Example: Entamoeba histolytica

  
• Aberrant parasite


  • Infect a host where they cannot develop further
  • Example: Toxocara canis

  
• Spurious parasite


  • Passes through the digestive tract without infecting the host
• Parthenogenetic parasite


  • Female parasite capable of reproducing eggs without being fertilized by a male and whose eggs contain larva that immediately hatches
• Coprophilic parasite


  • Able to multiply in fecal matter outside human body

  
• Hematozoic parasite


  • Those parasites that thrives inside red blood cells
  • Example: Plasmodia, Babesia, Leishmania

  
• Cytozoic parasite


  • Lives inside cells or tissues
  • Example: Trichinella spiralis

  
• Coelozoic parasite


  • Lives in body cavities
  • Example: Mansonella spp.

  
• Enterozoic parasite


  • Resides in intestines
  • Example: Tapeworms, Entamoeba histolytica

  
• Permanent parasite


  • Remains on or in the body of the host for its entire life
  • Usually endoparasites

  
• Temporary parasite


  • Lives on the host only for a short period of time
  • Usually ectoparasites
• Non-pathogenic parasite


  • aka Commensals, incapable of causing disease

  
• Pathogenic parasite


  • Disease causing parasites

  
• Classification of hosts

  • Definitive/Final host
  • Paratenic host
  • Accidental host
  • Reservoir host
  • Intermediate host
• Definitive/Final host


  • Parasite attain sexual maturity; host in which adult parasite lives
  • Example: Humans
• Paratenic host


  • One in which the parasite does not develop further to later stages. Parasite remains alive and is able to infect another host
  • Example: Frogs

  
• Accidental host


  • Host in which the parasite is not usually found

  
• Reservoir host


  • Harbors the asexual/larval stage of the parasite

  
• Intermediate host


  • Allows the parasite's life cycle to continue and become additional sources of infection

  
• Vector


  • Organisms that does not cause disease itself but which spreads infection by conveying pathogens from one host to another
• Classifications of vectors

  • Biologic
  • Mechanical/phoretic
• Sources of infection

  • Soil
  • Arthropods
  • Water
  • Food
  • Animals
  • Another individual
• Pseudomonas aeruginosa


  • Causes UTI, pneumonia, meningitis, sepsis, mild otitis (swimmer's ear), eye infection, folliculitis, wound infection
  • Produces water soluble pigments that produce the characteristic blue-green pus
  • Ecthyma gangrenosum - black necrotic lesion surrounding the wound
• Modes of transmission

  • Oral (fecal-oral)
  • Skin penetration
  • Arthropods
  • Congenital transmission
  • Transmammary infection
  • Inhalation of airborne eggs
  • Sexual intercourse
  • Iatrogenic transmission
• Oral (fecal-oral) is the most common method of transmission. Examples: Cestodes, Trematodes, Intestinal Protozoans are foodborne
• Hookworm and Strongyloides stercoralis enter upon exposure to soil through skin penetration
• Arthropods transmit parasites through their bites. Examples: Malaria, Filariasis, Leishmaniasis, Trypanosomiasis, Babesiosis

  
• Trophozoites can cross the placental barrier during pregnancy leading to congenital transmission
• Ancylostoma and Strongyloides may be transmitted through mother's milk