In biology, a host is an organism that harbors a parasite, mutual partner, or commensal partner, typically providing nourishment and shelter. Main article: Life There are many universal units and common processes that are fundamental to the known forms of life. ... A parasite is an organism that lives in or on the living tissue of a host organism at the expense of that host. ...

Examples: A cell can be host to a virus, a legume plant can be host to helpful nitrogen-fixing bacteria, an animal can be host to a parasitic worm, e.g., a nematode.

A primary host or definitive host is a host in which the parasite grows mature; a secondary host or intermediate host is a host that harbors the parasite only for a short transition period. For trypanosomes, the cause of sleeping sickness, humans are the primary host, while the tsetse fly is the secondary host. Cells in culture, stained for keratin (red) and DNA (green) The cell is the structural and functional unit of all living organisms, sometimes called the building blocks of life. ... A common alternate meaning of virus is computer virus. ... Subfamilies Faboideae Caesalpinioideae Mimosoideae References GRIN-CA 2002-09-01 The Family Fabaceae (also as Family Leguminosae) is a grouping of plants in the Order Fabales, and one of the largest families of flowering plants with 650 genera and over 18,000 species. ... Rhizobia (from the Greek words Riza = Root and Bios = Life) are soil bacteria that fix nitrogen (diazotrophy) after becoming established inside root nodules of legumes (Fabaceae). ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria Placozoa Subregnum Bilateria  Acoelomorpha  Orthonectida  Rhombozoa  Myxozoa  Superphylum Deuterostomia     Chordata (vertebrates, etc. ... WORM means Write Once, Read Many. ... Classes Adenophora    Subclass Enoplia    Subclass Chromadoria Secernentea    Subclass Rhabditia    Subclass Spiruria    Subclass Diplogasteria The roundworms (Phylum Nematoda) are one of the most common phyla of animals, with over 20,000 different described species. ... Genera Blastocrithidia Crithidia Endotrypanum Herpetomonas Leishmania Leptomonas Phytomonas Trypanosoma Wallaceina The Trypanosomatidae are a group of kinetoplastid protozoa, which are exclusively parasitic. ... Sleeping sickness or African trypanosomiasis is a parasitic disease in humans. ... For other uses, see Human (disambiguation). ... Binomial name Glossina morsitans The tsetse fly, Glossina morsitans, is a fly (order Diptera) that eats blood from animals, including humans. ...

The host range or host specificity of a parasite is the collection of hosts that an organism can utilize as a partner. In the case of human parasites, the host range influences the epidemiology of the parasitism or disease. For instance, the production of antigenic shifts in Influenza A virus can result from pigs being infected with the virus from several different hosts (such as human and bird). This co-infection provides an opportunity for mixing of the viral genes between existing strains, thereby producing a new viral strain. An influenza vaccine produced against an existing viral strain might not be effective against this new strain, which then requires a new influenza vaccine to be prepared for the protection of the human population¹. Antigenic shift is the process by which two different strains of influenza combine to form a new subtype which is characterized by a mixture of the surface antigens of the two original strains. ... Negatively stained flu virions. ... A bottle and a syringe containing the influenza vaccine. ... In biology, Strain can be used two ways. ...

Related topics

• Symbiosis
• Vector
• Intermediate host

Common Clownfish (Amphiprion ocellaris) in their magnificent sea anemone (Heteractis magnifica) home. ... Traditionally in medicine, a vector is an organism that does not cause disease itself but which spreads infection by conveying pathogens from one host to another. ... In parasitology, an intermediate host is an organism that is infected with a parasite that will not reproduce sexually within it, while a definitive host is one in which the parasite reproduces. ...

References

Note 1: Centers for Disease Control and Prevention (2004). The Influenza (Flu) Viruses:Transmission of Influenza Viruses from Animals to People. Retrieved 2005-02-26.