Introduction to Parasitology in Biology

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12 Questions

What is the defining characteristic of a microparasite?

Direct reproduction within its vertebrate host

Which type of parasite is known to be important as a vector transmitting pathogenic microorganisms?


What is the term for parasites that live within the body of the host?


Which organisms are generally excluded when using the term 'parasite' according to convention?

Viruses and fungi

What type of parasites are protozoa classified as?


Which term is used to describe the transmission of pathogenic microorganisms by parasites?


What type of parasite attacks an unusual host, such as Echinococcus granulosus in man?

Accidental parasite

Which type of host harbors the adult parasite and allows for sexual replication?

Definitive host

In a symbiotic relationship, how do both the host and the parasite interact?

Neither of the partners suffer harm from the association.

What does a facultative parasite do under unfavorable circumstances?

May live either parasitically or freely

What is the role of a paratenic host in a parasite's life cycle?

Survives but does not develop further

What is the main characteristic of commensalism in a host-parasite relationship?

Only parasite benefits without harm to the host

Study Notes


  • Parasitology is the area of biology concerned with the phenomenon of dependence of one living organism on another.
  • Medical parasitology deals with the parasites that infect humans, the diseases they produce, and the response generated by humans against them, as well as methods of diagnosis, prevention, and treatment.


  • A parasite is an organism that is entirely dependent on another organism, referred to as its host, for all or part of its life cycle and metabolic requirements.
  • Microparasites: small, unicellular, and multiply within their vertebrate host, often inside cells (e.g., protozoa).
  • Macroparasites: large, multicellular, and have no direct reproduction within their vertebrate host (e.g., helminths).

Classification of Parasites

  • Ectoparasites: live on the surface of the body (e.g., human louse, Pediculus humanus).
  • Endoparasites: live within the body of the host (e.g., all protozoan and helminthic parasites of humans).

Types of Endoparasites

  • Obligate parasites: organisms that cannot exist without a host (e.g., Toxoplasma gondii).
  • Facultative parasites: organisms that can live either a parasitic or free-living existence under unfavorable circumstances (e.g., Naegleria fowleri).
  • Accidental parasites: organisms that attack an unusual host (e.g., Echinococcus granulosus in humans).
  • Aberrant parasites: organisms that attack a host where they cannot live or develop further (e.g., Toxocara canis in humans).


  • Host: an organism that harbors the parasite and provides nourishment and shelter.
  • Definitive host: harbors the adult parasite, where the parasite replicates sexually.
  • Intermediate host: the host that alternates with the definitive host and harbors the larval or asexual stages of a parasite.
  • Paratenic host: a host in which the larval stage of a parasite survives but does not develop further.
  • Reservoir host: can harbor a pathogen indefinitely with no ill effects.
  • Compromised host: one in whom normal defense mechanisms are impaired (e.g., AIDS).

Host-Parasite Relationships

  • Symbiosis: an association in which both host and parasite are dependent on each other, with no harm to either partner.
  • Commensalism: an association in which only the parasite benefits, with no detectable damage to the host.
  • Parasitism: one partner (the parasite) harms or lives on the expense of the other (host).

Classification of Animal Parasites and Vectors

  • Taxonomic classification: Subphylum, Class, Order, Family, Genus, Species.
  • Species: a population with essentially the same genetic characters, capable of continued reproduction, but usually cannot interbreed with other species.

Explore the field of parasitology in biology, focusing on the dependence of organisms on each other, especially in medical contexts. Learn about parasites, their impact on human health, and methods for diagnosis, prevention, and treatment.

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