infection

n.

invasion of the body by harmful organisms (pathogens), such as bacteria, fungi, protozoa, rickettsiae, or viruses. The infective agent may be transmitted by a patient or carrier in airborne droplets expelled during coughing and sneezing or by direct contact, such as kissing or sexual intercourse (see sexually transmitted disease); by animal or insect vectors; by ingestion of contaminated food or drink; or from an infected mother to the fetus during pregnancy or birth. Pathogenic organisms present in soil, organisms from animal intermediate hosts, or those living as commensals on the body can also cause infections. Organisms may invade via a wound or bite or through mucous membranes. After an incubation period symptoms appear, usually consisting of either localized inflammation and pain or more remote effects. Treatment with antibiotics is usually effective against most infections, but there are few specific treatments for many of the common viral infections, including the common cold (see antiviral drug, interferon).