Parasitology Prelim

• Populations at risk for contracting parasites:

  • Individuals in underdeveloped areas and countries
  • Refugees
  • Immigrants
  • Visitors from foreign countries
  • Immunocompromised individuals
  • Individuals living in close quarters (e.g., prisons)
  • Children who attend schools
• Incidence – number of new cases of infection appearing in a population in a given period of time
• Prevalence – number (usually expressed as percentage) of individuals in a population estimated to be infected with a particular parasite species at a given time
• Intensity of infection – number of worms per infected individual
• Symbiosis

  Living together; between organisms from different species
• Commensalism

   

  Two different species of organism that is beneficial to one and neutral to the other (eg. Entamoeba coli)
• Mutualism

   

  two different species of organisms that is beneficial to both

  (eg. Termites and the flagellates in their digestive system)
• Parasitism

   

  Two different species of organism that is beneficial to one at the other’s expense (eg. Entamoeba histolytica)
• Commensal

  Relating to commensalism; the association between two different organisms in which one benefits and has a neutral effect on the other
• Pathogenic

  Parasite that has demonstrated the ability to cause disease
• Obligatory Parasite

  Parasite that cannot survive outside of a host

   

  Eg. Tapeworms
• Facultative Parasite

  Parasite that is capable of existing independently of a host

   

  Eg. Candida; acanthamoeba
• Endoparasite

  (Infection)

  Parasite that is established inside of a host

   

  Eg. Tapeworms
• Ectoparasite

  (Infestation)

  Parasite that is established in or on the exterior surface of a host

   

  Eg. Flea, lice, tick
• Accidental Parasite

  A parasite, which establishes itself in a host where it does not ordinarily live
• Permanent Parasite

  remains on or in the body of the host for its entire life
• Temporary Parasite

  lives on the host only for a short period of time
• Spurious Parasite

  a free-living organism that passes through the digestive tract without infecting the 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/ Asymptomatic Host

  Host harboring parasites that are parasitic for humans and from which humans may become infected (Pigs are reservoirs of Balantidium coli, field rats of Paragonimus westermani, and cats of Brugia malayi)
• Paratenic/ Transport Host

  Host in which parasites do not develop further to later stages;  responsible for transferring a parasite from one location to another (Paragonimus metacercaria in raw wild boar meat can pass through the intestinal wall of humans and complete its development.)
• Carrier

  Parasite-harboring host that is not exhibiting any clinical symptoms but can infect others
• Biologic Vector

  transmits the parasite only after the latter has completed its development within the host
• Biologic Vector

  not only transports the pathogen but also plays a role in the life cycle of a pathogen
• Biologic Vector - ex. Aedes mosquito (host-vector-host)
• Mechanical/ Phoretic Vector

  only transports the parasite
• Mechanical/ Phoretic Vector

  ex. Flies and cockroaches (vector-food-humans)
• 3 common components

  ·       Mode of Transmission

  ·       Infective Stage – a morphologic form that invades humans

  ·       Diagnostic Stage – one (or more) forms that can be detected via laboratory retrieval methods,
• Exposure

  Process of being exposed to an infective agent
• Infection

  Invasion of tissues by pathogens, their multiplication and the reaction of host tissues to the infectious agent
• Autoinfection

  Results when an infected individual becomes his own direct source of infection
• Superinfection

  Happens when the already infected individual is further infected with the same species leading to a massive infection with the parasite
• Phylum → Classes → Orders, Families, Genera, and Species