Infection
Infection, injurious contamination of the body or part of the body by pathogenic agents, such as fungi (see Fungus Infections ), bacteria, protozoa, rickettsiae, or viruses, or by the toxins that these agents may produce. An infection may be local and confined to one area or generalized and spread throughout the body. Once the infectious agent enters the host and begins to proliferate, the defense mechanisms of the body react to the infection, producing the characteristic symptoms of pain, swelling, reddening at the site of infection, functional disorders, rise in body temperature and pulse rates, and an increase in the number of white cells (see Immune System ). Infectious agents may enter the body of the host by several routes. The most common route is through the respiratory passages, urinary tract, and gastrointestinal tract, but other common entry routes are through the skin, especially injured skin, the mucosal surfaces of other body openings, and the conjunctiva of the eyes. Pre...