Damian, Raymond T. Department of Zoology, Franklin College of Arts and Sciences, University of Georgia, Athens, Georgia.
Last reviewed:January 2021
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- Parasite–host relationships
- Parasite–parasite relationships
- Physiologic interactions
- Related Primary Literature
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The scientific study of parasites and parasitism. Parasitology is the branch of biology dealing with parasitic organisms (see illustration), with particular focus being directed toward understanding the relationship between the parasite and the host. Parasitism is a type of symbiosis and is defined as an intimate association between an organism (parasite) and another, larger species of organism (host) upon which the parasite is metabolically dependent. Implicit in this definition is the concept that the host is harmed, whereas the parasite benefits from the association. Because well-adapted parasites may be nonpathogenic, parasitism merges into another type of symbiosis in which both partners benefit, that is, mutualism. Parasitism also blends with another ecological relationship, that is, predation. For example, ichneumon fly larvae, which ultimately kill their caterpillar hosts by internal consumption, are indeed predators, but are called parasitoids, reflecting the similarity of their lifestyle to true parasitism. By the definition, then, most species of organisms may properly be called parasites. Pathogenic bacteria and viruses, as well as fungal and insect parasites of plants, are traditionally outside the field of parasitology, although they technically are parasites. See also: Medical parasitology; Population ecology; Predator-prey interactions
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