Introduction to Parasitology

• Symbiosis


  A relationship where unlike organisms exist together
• Types of symbiotic relationships


  • Commensalism
  • Mutualism
  • Parasitism
• Commensalism


  A form of symbiotic relationship in which two species live together and one species benefits from the other without harming or benefitting the other
• Mutualism


  A symbiotic relationship in which two organisms mutually benefit from each other
• Parasitism


  A form of symbiotic relationship where one party or symbiont(parasite) benefits to the detriment (damaging) of the host.
• In almost all cases of parasitic relationships, the parasite deprives the host of essential nutrients and produce disease in the host
• Parasitism


  The relationship between a parasite and its host
• Elements in parasitism


  • Parasite
  • Host
• Parasites


  • Usually depend on the host for survival
  • Classified in several ways
• Classification of parasites based on habitat

  • Ectoparasites (live outside host's body)
  • Endoparasites (live inside host's body)
• Infestation


  Invasion of the body by ectoparasites
• Infection


  Invasion of the body by endoparasites, resulting from entry and multiplication of the parasite within the host
• Classification of parasites based on ability to live independently


  • Facultative parasites (can live independently)
  • Obligate parasites (must live inside a host)
• Classification of parasites based on mode of living

  • Permanent parasites (remain in host from early life to maturity)
  • Intermittent parasites (visit host during feeding time)
  • Incidental parasites (occur in unusual host)
  • Transitory parasites (larva develops in host, adult is free-living)
  • Erratic parasites (seen in unusual organ)
• Hosts


  Organisms that harbor the parasite and provide nourishment
• Types of hosts


  • Definitive hosts (harbor adult stage or sexual phase)
  • Intermediate hosts (harbor larval stage or asexual stage)
  • Reservoir hosts (harbor parasite and act as additional source of infection)
• Migratory birds serve as the reservoir host for vectors so that the infective stage of a certain parasite may reach its final host
• Sources of Exposure to Infection or Infestation

  • Contaminated soil or water
  • Food containing the parasite's infective stage
  • A blood-sucking insect
  • A domestic or wild animal harboring the parasite
  • Another person and his or her clothing, bedding, or the immediate environment he or she has contaminated
  • One's self (auto-infection)
• Most common source of exposure to infection

  Soil contaminated or polluted with human feces
• Source of viable cysts of the parasitic amoebae and intestinal flagellates, the larvae of the blood flukes, and the eggs of the pork tapeworm Taenia solium


  • Water
• Source for the fish tapeworm Diphyllobothrium latum, as well as other intestinal and liver flukes


  • Freshwater fish
• Source of Trichinella spiralis and Taenia solium


  • Raw pork
• Source of Taenia saginata


  • Improperly cooked or raw beef
• Terms associated with parasite-host relationships

  • Obligatory parasite
  • Facultative parasite
  • Endoparasite
  • Ectoparasite
  • Accidental or incidental host
  • Definitive host
  • Intermediate host
  • Reservoir host
  • Transport/Paratenic host
• Obligatory parasite


  Parasite that cannot survive outside the host
• Facultative parasite


  Parasite capable of existing independently of the host
• Endoparasite


  Parasite that is established inside the host
• Ectoparasite


  Parasite that is established in or on the exterior surface of host
• Accidental or incidental host


  Host other than the normal one that is harboring a parasite
• Definitive host


  Host in which the adult/sexual phase of parasite development occurs
• Intermediate host


  Host in which the larval/asexual phase of parasite development occurs
• Reservoir host


  Host harboring parasites that are parasitic for humans and from which humans may become infected
• Transport/Paratenic host


  Host responsible for transferring a parasite from one location to another
• Types of parasite-host relationships

  • Symbiosis
  • Commensalism
  • Mutualism
  • Parasitism
• Symbiosis


  Living together, the association of two living organisms, each of different species
• Commensalism


  Association of two different species of organisms that is beneficial to one and neutral to the other
• Mutualism


  Association of two different species of organisms that is beneficial to both
• Parasitism


  Association of two different species of organisms in which one benefits at the other's expense
• The relationship of the body and it’s normal flora is considered as: commensalism
• The example of normal intestinal flora(producing vitamin K) which is used for the body’s clotting factors is a what type of symbiotic relationship?

  mutualism