General Considerations in Parasitology

• Symbiosis


  Living together
• Symbiosis


  • A close relationship exists between two dissimilar organisms living together on a single host (eg; algae and fungi on lichens)
  • Any two organisms living in close associations, commonly one living in or on the body of the other
• Commensalism


  • Also termed as "Phoresis"
  • Exists when two symbionts are merely "traveling together" without physiological or biochemical dependence on the part of either participants
  • A relationship that gives benefit to the parasite but without reciprocating and without giving injury to the host
• Commensalism


  • Tapeworms consume waste products of the host imposing no harm on it
• Mutualism


  • A relationship in which both partners benefit from the associations
  • Usually an obligatory relationship
• Mutualism


  • Termite and its intestinal flagellate fauna
  • The termite benefits because it could not digest its cellulose-containing food without the flagellate and the intestinal organism benefits by having a secure habitat (also for food)
• Parasitism


  • A relationship that is beneficial to one (parasite) at the expense of the other (host)
  • Effects: 1. Cause mechanical injury, 2. Stimulates damaging inflammatory or immune response, 3. Robbing the host of nutrition
• Predators


  Which attacks or kill, usually on smaller or weaker animal (prey) in order to obtain food
• Parasitoids


  • Are insects (flies or wasps) whose immature stages feed on their host's bodies (other insects), but finally kill the host
  • Resembles predators, but they require a single host individual
• Parasitology is a branch of biology concerned with the phenomenon of dependence of one loving organism on another
• Medical Parasitology


  Concerned primarily with the animal parasites of humans and their medical significance, as well as their importance in human communities
• Host


  • Any living organism from which a parasite obtain nourishment and protection
  • An organism that harbors the parasite
  • In a majority of instances, only one host is required for a parasite to carry on its life cycle
• Parasite


  • Any organism that lives in or on the body surface of another organism (host), which is usually larger organism that provides physical protection (shelter) and nourishment (food) for survival
  • 1. Definitive/Final Host, 2. Intermediate Host, 3. Reservoir Host, 4. Paratenic Host
• Definitive/Final Host


  The one that harbors the sexual or the adult stage of the life cycle of the parasite
• Intermediate Host


  Harbors the infective stage of the parasite
• Intermediate Host


  • Molluscs (snails)
• Reservoir Host


  • May be as in environment, plants, and animals
  • Host that harbors a parasite that lives within or on body surfaces long enough to serve as a source of infection
  • They allow the parasite's life cycle to continue and become additional sources of human infection
• Reservoir Host


  • Rodents and wild carnivores (Trichinella)
  • Domestic dogs (Leishmania spp.)
  • Armadillos (Trypanosoma cruzi)
• Paratenic Host


  • A host that harbors the infective larval stage of a parasite in which no essential growth or development takes place although infectivity is preserved, in the (intermediate) host
  • It serves as a means of transport for the infective larval stage to reach its final host
• Paratenic Host


  • Dogs and cats
• Parasites classified according to

  • Habitat / State of Parasitosis
  • Pathogenecity
  • Relationship of Parasite to Host
• Endoparasites


  • Also termed as "Infection"
  • Parasites that are found inside the body of a host
• Ectoparasites


  • Termed as "Infestation"
  • Parasites that are attached to the skin or that temporarily invade the superficial tissues of the host's body
• Pathogens


  Parasites that are harmful, frequently causing local or systemic damage to a host's tissues
• Superinfection


  When an individual harboring a parasite is reinfected with the same species of parasite
• Autoinfection


  When the infected individual is his own direct source of the re-exposure, which maybe external (perianal or anus – to -mouth via fingers) or internal in the mode of infection
• Non-pathogens (Commensals)


  • Parasites living in apparent harmony with a host
  • Those that get benefits from the host, but without reciprocating and giving injury to the host
• Obligate Parasites


  Organisms that cannot exist or survive without a host
• Obligate Parasites


  • Ascaris lumbricoides
• Facultative / Opportunist Parasites


  Organisms that, under favorable conditions, may live either a parasitic or free – living existence
• Facultative / Opportunist Parasites

  • Strongyloides stercolralis
• Amphizoic


  Are free – living organisms that may invade and colonize in the human body
• Amphizoic


  • Micronema, Naegleria, and Acanthamoeba
• Spurious parasite


  • Are free - living organisms having merely passed through the intestine, and recovered either in a living or dead state from a human feces
  • Non – human pathogens
• Intermittent / Temporary Parasite


  Organisms that visit or come at interval to its host during feeding time
• Intermittent / Temporary Parasite

  • Mosquitoes and Bedbugs
• Permanent Parasite


  Parasites that live their entire adult lives within or on their hosts
• Accidental / Incidental Parasite


  A parasite that enters or attaches to the body of a species of host different from its normal one
• Accidental / Incidental Parasite


  • Toxocara canis
• Hyperparasitism


  When parasite host other parasite