mc3_chapt4

• 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
• Host


  An organism that is entirely dependent on another organism (host)
• Pathogenic mechanism of parasitic infection

  • Varies according to species and quantity of parasites as well as parasite-host adaptation and host responses
  • Damage can be either confined within the parasitic site or extend into other parts in host
  • Commonly caused by mechanical pressure, capturing nutrition, toxins, responses and anaphylaxis of host to the stimulation from parasites as well as passage for other pathogens invading the 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 its life cycle, while parasites will have to depend on their host to complete their life cycle
• Pathogenicity


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


  A kind of interaction between two species, where one species is benefitted, and the other is harmed
• Definitive or Primary Host

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

  
• Definitive hosts


  • Sheep for Fasciola gigantica, a dog for Echinococcus granulosus, and a female anopheles mosquito for Plasmodium spp.

  
• 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
• Symbiotic relationships


  Close proximity and dependence between organisms (host and parasite) for their survival

  
• 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
• Commensalism


  A symbiotic relationship where one partner benefits while the other is neither helped nor harmed
• Adaptation


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


  • Feeding organs usually absent
  • Presence of well-developed piercing devices
  • Restricted movements, locomotory organs generally absent or highly reduced
  • Presence of attachment organs like rostellum, hooks or suckers
  • Resistant outer covering
  • Highly muscular pharynx for easy absorption of food materials
• Types of parasites


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

  
• The three main classes of parasites that can cause disease in humans are protozoa, helminths, and ectoparasites

  
• Protozoa


  Microscopic, one-celled organisms that can be free-living or parasitic in nature, able to multiply in humans and transmitted through fecal-oral route or by arthropod vectors

  
• Types of protozoan parasites

  • 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, can be either free-living or parasitic

  
• Ectoparasites


  Parasites that live on the surface of the host's body

  
• Protozoa


  Microscopic, single-celled organisms that are able to multiply in humans, contributing to their survival and permitting serious infections to develop from just a single organism
• Transmission of protozoa that live in a human's intestine

  Typically occurs through a fecal-oral route

  
• Protozoa that live in the blood or tissue of humans

  Transmitted to other humans by an arthropod vector (e.g. bite of a 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 either free-living or parasitic in nature, cannot multiply in humans

  
• Main groups of helminths

  • Flatworms (Platyhelminths - trematodes (flukes) and cestodes (tapeworms))
  • Thorny-headed worms (Acanthocephalins - reside in gastrointestinal tract)
  • Roundworms (Nematodes - can reside in gastrointestinal tract, blood, lymphatic system or subcutaneous tissues)

  
• 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
• Endocrine glands include the pituitary gland (hypophysis), thyroid gland, parathyroid glands, adrenal glands, pancreas, ovaries/testes, thymus, pineal body, and placenta.