Introduction to Parasitology

• Association

  Interactions bring about different levels of associations
• Types of associations

  • Homospecific
  • Heterospecific
  • Homogenetic
  • Heterogenetic
• Homospecific or homogenetic

  • Association between organisms of the same species or genotype
• Homospecific associations

  • Herds
  • Colonies
  • Flocks
• Heterospecific or heterogenetic


  • Association between different species or genotypes of animals
• Symbiosis

  Living together; involves different levels of intimacy
• Types of symbiotic associations

  • Phoresis
  • Commensalism
  • Mutualism
  • Parasitism
• Phoresis

  An association in which one organism provides shelter, support or transport for another organism
• Commensalism

  An association in which the commensal benefits by feeding on the food remains of the host
• Mutualism

  Association in which both the symbiont and the host benefit
• In mutualism, the two associates cannot survive without one another
• Introductory parasitology is the study of organisms that live by dwelling on other organisms
• Parasites

  • They have a complex cellular organization
  • They have membrane bound organelles
  • They have the basic structure of an animal cell
• Characteristics of prokaryotic organisms

  • No nucleus
  • Simple membrane
  • One chromosome
  • No organelles
  • Peptidoglycan in cell wall
• Types of parasites

  • Endoparasites
  • Ectoparasites
• Ectoparasites

  • Fleas
  • Lice
  • Ticks
• Some parasites fall into both endoparasite and ectoparasite groups
• Protozoans

  • Are single celled (unicellular)
  • Have projecting locomotory structures like pseudopodia, cilia and flagella
  • Ciliates have both micro and macro nuclei
• Metazoans

  • Are multicellular
  • Can be round (roundworm)
  • Can be tape-like (tapeworms)
  • Can be leaf-like
• Stages of Metazoans

  • Egg
  • Larvae
  • Adult
• Definitive Host

  Host in which sexual reproduction/maturity occurs
• Intermediate Host

  Species of host other than the definitive host
• Paratenic or Transport/Transfer Host

  The host used as a temporary hideout until an appropriate definitive host is encountered
• Reservoir Host

  The host that harbours parasites that could be transmitted to humans
• Vectors

  Blood-feeding arthropod intermediate hosts that aid in disease transmission
• Zoonosis

  Infection in which the normal host is an animal but can cause disease in humans if accidentally infected
• Reproduction in Protozoans

  1. Binary fission

  2. Conjugation

  3. Multiple fission

  4. Schizogony

  5. Sporogony
• Binary fission

  Organism divides into two (Duplication)
• Conjugation

  Common in ciliates where two individuals come together, with changes in both macro and micronuclei
• Sporogony

  Occurs after the fusion of gametes (fertilization); involves encystation of the zygote to form oocysts
• Schizogony


  Leads to production of uni-nucleate daughter cells (merozoites)
• Humans are the definitive host of Guinea worm
• Apicomplexa is a group of protozoans
• Parasites can be classified into three categories based on their location within the body of the host:
• The term "parasite" comes from the Greek word parastētēs meaning one who eats at someone else's table