Chap 4: Parasitology

• Parasitology


  The study of the interaction between parasites and their hosts

  
• Parasitologists tend to concentrate on eukaryotic parasites, such as lice, mites, protozoa and worms, with prokaryotic parasites and other infectious agents the focus of fields such as bacteriology, microbiology and virology

  
• Parasite


  A living organism which receives nourishments and shelter from another organism where it lives
• Criteria used in classification of parasites

  • According to their pathogenicity
  • According to their need of host
  • According to their location
  • According to their mode of living

  
• Pathogenicity


  The ability of an organism to infect another organism (host)
• Pathogen


  An organism that causes diseases to the host after infection
• Parasite


  An organism that lives on or in another organism of another species, usually deriving nutrients at the expense of its host
• Pathogens usually kill their host through diseases, while most parasites do not kill their host but do cause some damage
• Pathogens typically do not require a host to complete their life cycle, while parasites will have to depend on their host to complete their life cycle
• Definitive or Primary Host

  The host which harbors the adult parasites or where the parasite replicates sexually

  
• Intermediate or Secondary Host


  The host which harbors the larval stages of a parasite or in which the parasite undergoes asexual multiplication

  
• Reservoir Host


  A host which harbors the parasites, possibly grow, and multiply and serves as an important source of infection to other susceptible hosts
• Paratenic or Storage Host


  A host that serves as a temporary refuge and vehicle for reaching an obligatory host, usually the definitive host
• Incidental or Accidental Host


  A host organism that shelters the parasite, but since it can't progress the life cycle development, it is dead-end for it
• Mutualism


  A symbiotic relationship where both organisms benefit from each other's existence
• Parasitism


  A non-mutual symbiotic relationship where the parasite benefits at the expense of the host, while the host is harmed
• Commensalism


  A symbiotic relationship where one partner benefits whereas the second partner (the host) are neither helped nor harmed
• Parasitic adaptation


  • Any feature of an organism or its part which enables it to exist under conditions of its habitat

  
• Structural adaptations of parasites

  • Feeding organs are usually absent in endoparasites
  • Presence of well-developed piercing device in some parasites
  • Locomotory organs are generally absent or highly reduced in endoparasites
  • Presence of attachment organs such as rostellum, hooks or suckers
  • Outer covering is resistant to enzymatic digestion of the host
  • Some endoparasites have highly muscular pharynx for easy absorption of food materials

  
• Classification of parasites


  • Ectoparasite
  • Endoparasite
  • Permanent parasite
  • Temporary parasite
  • Facultative parasite
  • Obligatory parasite
  • Occasional parasite

  
• Three main classes of parasites that can cause disease in humans

  • Protozoa
  • Helminths
  • Ectoparasites

  
• Protozoa


  Microscopic, one-celled organisms that can be free-living or parasitic in nature, able to multiply in humans
• Four groups of protozoa infectious to humans based on mode of movement

  • Sarcodina (ameba)
  • Mastigophora (flagellates)
  • Ciliophora (ciliates)
  • Sporozoa (non-motile adult stage)

  
• Helminths


  Large, multicellular organisms that are generally visible to the naked eye in their adult stages, cannot multiply in humans
• Three main groups of helminths

  • Flatworms (Platyhelminths)
  • Roundworms (Nematodes)
  • Thorny-headed worms (Acanthocephala)

  
• Protozoa


  Microscopic single-celled organisms that can live in a human's intestine or blood/tissue

  
• Transmission of protozoa that live in a human's intestine

  Fecal-oral route

  
• Transmission of protozoa that live in the blood or tissue of humans

  Arthropod vector (e.g. bite of mosquito or sand fly)

  
• Groups of protozoa infectious to humans based on mode of movement

  • Sarcodina (ameba, e.g. Entamoeba)
  • Mastigophora (flagellates, e.g. Giardia, Leishmania)
  • Ciliophora (ciliates, e.g. Balantidium)
  • Sporozoa (organisms whose adult stage is not motile, e.g. Plasmodium, Cryptosporidium)

  
• Helminths


  Large, multicellular organisms generally visible to the naked eye in their adult stages, can be free-living or parasitic, cannot multiply in humans

  
• Main groups of helminths

  • Flatworms (Platyhelminths - trematodes and cestodes)
  • Thorny-headed worms (Acanthocephalins)
  • Roundworms (Nematodes)

  
• Ectoparasites


  Organisms such as ticks, fleas, lice, and mites that attach or burrow into the skin and remain there for relatively long periods of time

  
• Arthropods are important in causing diseases in their own right, but are even more important as vectors, or transmitters, of many different pathogens that in turn cause tremendous morbidity and mortality from the diseases they cause
• Acanthamoebiasis


  Infection caused by a tiny ameba that can affect the eye, skin, and brain

  
• Babesiosis


  Disease caused by parasites carried by ticks, affects red blood cells
• Balantidiasis


  Disease transmitted by Balatidium coli, a single-cell parasite that mostly infects pigs but can cause intestinal infections in humans

  
• Blastocystosis


  Illness that affects the intestines, transmitted via the fecal-oral route
• Coccidiosis


  Disease that affects the human intestines, transmitted through the fecal-oral route. Generally affects cats and dogs
• Amoebiasis


  Disease caused by the parasite Entamoeba histolytica, attacks the intestines

  
• Giardiasis


  Disease that affects the lumen of the small intestine, transmitted through contaminated water/food