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THE DYNAMICS OF DISEASE TRANSMISSIONChapter two
The Epidemiologic Triangle
The Epidemiologic TriangleAgent: the cause of the disease (bacteria, virus, parasite, fungus, mold, chemical, solvent, radiation, heat, nutritional deficiency, rattlesnake poison)Host: an organism that harbors a disease (human or animal)Environment: those favorable surroundings and conditions external to the human or animal that cause or allow disease transmission (biological, social, cultural, physical aspects of the
Infectious DiseasesAll illness due to a specific infectious agent that is spread from an infected person, animal, or inanimate reservoir to a susceptible host, either directly or indirectly, through an intermediate plant or animal host, vector, or the inanimate environment
Pathogenpath·o·gen (păth'ə-jən) n.An agent that causes disease, especially a living microorganism such as a bacterium or fungus.
Bacteriabac·te·ri·um (băk-tîr'ē-əm) n., pl.-te·ri·a (-tîr'ē-ə). Any of the unicellular prokaryotic microorganisms of the class Schizomycetes, which vary in terms of morphology, oxygen and nutritional requirements, and motility, and may be free-living, saprophytic, or pathogenic in plants or animals.[New Latin bactērium, from Greek baktērion, diminutive of baktron,
Virusvi·rus (vī'rəs) n., pl.-rus·es. Any of various simple submicroscopic parasites of plants, animals, and bacteria that often cause disease and that consist essentially of a core of RNA or DNA surrounded by a protein coat. Unable to replicate without a host cell, viruses are typically not considered living organisms. A disease caused by a virus.[Latin vīrus, poison.]
Fungusfun·gus (fŭng'gəs) n., pl.fun·gi (fŭn'jī, fŭng'gī) or fun·gus·es. Any of numerous eukaryotic organisms of the kingdom Fungi, which lack chlorophyll and vascular tissue and range in form from a single cell to a body mass of branched filamentous hyphae that often produce specialized fruiting bodies. The kingdom includes the yeasts, molds, smuts, and mushrooms.[Latin; perhaps akin to Greek spongos, sphongos, sponge.]
Parasitepar·a·site (păr'ə-sīt') n.Biology.An organism that grows, feeds, and is sheltered on or in a different organism while contributing nothing to the survival of its
Protozoaprotozoa (proh-tuh-zoh-uh) Single-celledanimals, such as amoebas, that are the most primitive form of animal life. In modern biology, they are classified in the kingdomof Protoctistarather than in the animal kingdom.