∞ generated and posted on 2016.01.27 ∞

Organism that lives in or on other organisms from which it is stealing resources and to which it is causing harm.

Harm as used here is essentially meaning to cause damage such as that can result in disease and/or reduced fitness as displayed by the host organism, that is, the organism that is being . Bacterial as well as viral parasites are known as pathogens.

See also parasitism along with symbiosis. Contrast with mutualism as well as commensalism.