An infection is the detrimental colonization of a host organism by a foreign parasite species. Infecting organisms seeks to utilize the host'sresources to multiply, usually at the expense of the host. The infecting organism, or pathogen, interferes with the normal functioning of the host and can lead to chronic wounds, gangrene, loss of an infected limb, and even death. The immune system of mammalian hosts reacts to infections with an innate response, often involving inflammation, followed by an adaptive response. Colloquially, a pathogen is usually considered a microscopic organism though the definition is broader, including macroparasites, fungi, viruses, prions, bacteria, and viroids. Asymbiosis between parasite and host, whereby the relationship is beneficial for the former but detrimental to the latter, is characterised asparasitism. The branch of medicine that focuses on infections and pathogens is infectious disease. "When infection attacks the body,anti-infective drugs can help turn the tide of battle. Four types of anti-infective or drugs exist: antibacterial (antibiotic), antiviral, antitubercular, and antifungal.