Parasite

From Freepedia

A parasite is an organism that lives in or on the living tissue of a host organism at the expense of that host. The biological interaction between the host and the parasite is called parasitism. Parasitism is a type of symbiosis, by one definition, although another definition of symbiosis excludes parasitism, since it requires that the host benefit from the interaction as well as the parasite.

Parasites are generally smaller than their hosts, absorbing nutrients from the host's body fluids, but this is far from a universal strategy. Organisms whose life cycle guarantees the death of the host are not called parasites, but are parasitoids. A few parasites have hosts which are themselves parasites. These are called hyperparasites.

There are two types of ecto- and endoparsitoids, koinobionts and idiobionts. Koinobiont parasitoids do not kill their hosts until the host has continued to develop to a further stage (for example from egg to larva). Idiobiont parasitoids kill their hosts at the infected stage. These terms are frequently used to describe parasitoids of insect hosts, which develop in distinct stages.

Parasite is also the term for a partially formed conjoined twin which lacks a separate brain, or an extra head which may grow from the side of the head or the palate.

Certain types of DNA, such as transposable elements and B chromosomes, may also be considered as parasites of the host genome.

Examples

• Endoparasites (endo = within; parasites that live inside their hosts)
  • Plants
    • Rafflesia
  • Animals
    • Acanthocephala
    • Candiru (Vampire fish of Brazil)
    • Clonorchis sinensis (the Chinese liver fluke)
    • Cymothoa exigua
    • Dracunculiasis (Guinea Worm Disease)
    • Enterobius vermicularis
    • Strepsiptera
    • Strongyloides stercoralis
  • Fungi (such as ringworm)
    • Gymnosporangium and other rusts
  • Protists (Protozoa)
    • Malaria (a common blood disease caused by plasmodium)
    • Sleeping sickness, Chagas disease and leishmania, caused by kinetoplastid protists of the Trypanosoma and Leishmania genera.
    • Balantidium coli (the only ciliated protozoan to infect humans)
    • Giardia lamblia (the most common intestinal protozoan in the United States)
    • Entamoeba histolytica (causes Amebiasis, common in developing countries)

• Ectoparasites (ecto = outside; parasites that live on but not within their hosts, for example, attached to their skin)
  • Plants
    • Cuscuta
    • Mistletoe
    • Toothwort
    • The wood rose, Dactylanthus taylorii
  • Animals
    • Hirudinea (some leeches)
    • Phthiraptera (Lice)
    • Siphonaptera (Fleas)
    • Acarina (Ticks)
    • Tantulocarida

Many lifeforms are parasitic only during a part of their lifecycle. Many cuckoos, for example, are brood parasites: their young are parasitic on the host species, but adult cuckoos fend for themselves.

See also

• Intestinal parasite
• Saprophyte
• Malarial parasite
• Teratology
• Successful parasite

References

• Centers for Disease Control and Prevention
  • Division of Parasitic Diseases
    • DPDx - Laboratory Identification of Parasites of Public Health Concern - Reference and Training as well as Diagnostic Assistance