Symbiosis is a long-term or permanent cohabitation of two or more organisms, usually bring mutual benefits. The most famous example of symbiosis - lichens (symbiosis of algae and fungi). When indifferent contact occurs only unilateral use without harm to another boyfriend ("nhlengethwa", or kommensalizmom: Cirripedia crustaceans settle on the skin of whales). The concept of symbiosis somewhat arbitrarily, as it can when the changed conditions to become predation or parasitism.
Pathogens of humans and warm-blooded animals (viruses, rickettsiae) often are also commensals arthropods (insects, ticks). Amoeba dysentery, usually present in the content of large intestine people as harmless a symbiote, under certain conditions may cause a person to severe parasitic disease amebiasis.