An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease. Colloquially, infections are usually considered to be caused by microscopic organisms or microparasites like viruses, prions, bacteria, and viroids, though larger organisms like macroparasites and fungi can also infect. Hosts normally fight infections themselves via their immune system. Mammalian hosts react to infections with an innate response, often involving inflammation, followed by an adaptive response...