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Parasitology –Some terms and definitions 


A. Endoparasite - Lives within host eg. Leishmania

  1. Obligate endoparasite   — can't exist without parasitic life eg. Toxoplasma gondii
  2. Facultative endoparasite — parasitic or freeliving —4 can live either eg. Naeglaria
  3. Accidental endoparasite — attacks unusual host eg. Echinococcus
  4. Aberrant endoparasite  — parasite during its migration (in host) reaches a site where it can't live/ develop further eg. Toxocara canis  

B. Ectoparasite : Lives on outer surface or in superficial tissue eg lice (Infestation)

Host — Org. which harbors parasite, provides nutrition, shelter

  1. Definitive —
    a.  Harbours — Adult parasite
    b.  Harbours most highly dev. form
    c.   Where sexual replic occurs
  2. Intermediate — Harbours Asexual form
  3. Reservoir host — Harbours parasite Imp. source of Inf. to other host
  4. Paratenic host — Harbours parasite without any further dev. 

Protozoa — Unicellular, Eukaryotes, Single cell performs all functions – Flagella/Pseudopodia/Cilia are the organs of locomotion and may provide immunity to re-infection


C.  Taxonomy

The classification of the medically important parasites is as follows

1.  Subkingdom Protozoa: 45,000 unicellular species, each defined in the phylum according to organelles, locomotion, life cycle and type of reproduction.

  1. Phylum Sarcomastigophora.
    1. Subphylum - Mastigophora: movement with flagella - e.g. Trichomonas, Giardia
    2. Subphylum - Sarcodina: pseudopodia, e.g. amoeba 
  2. Phylum Apicomplexa: apical complex, no locomotor apparatus; sexual reproduction, e.g.
  3. malaria, Isospora, Toxoplasma
  4. Phylum Ciliophora: movement with cilia, e.g. Balantidium.
  5. Phylum Microspora: e.g.   Enterocytozoon 

2.  Subkingdom - Metazoa (multicellular organisms)

a.  Phylum – Nemathelminthes

  1. Nematodes: round worms, round in cross section; separate sexes; complete digestive tract; 500,000 species only a few parasitic to man; e.g. hookworm., filaria

b.  Phylum - Platyhelminthes: flat worms; incomplete or absent digestive tract; no body cavity; mostly hermaphroditic.

  1. Class Trematoda: flukes; leaf shaped unsegmented body,  often complex life cycle; e.g. lung fluke.
  2. Class Cestoidea: tapeworms; segmented bodies each segment containing complete set of male and female reproductive organs; no alimentary tract, nutrition by absorption through body wall. e.g. beef tape worm.

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