/in fek"sheuhn/, n.
1. an act or fact of infecting; state of being infected.
2. an infecting with germs of disease, as through the medium of infected insects, air, water, or clothing.
3. an infecting agency or influence.
4. an infectious disease: Is this infection very dangerous?
5. the condition of suffering an infection.
6. corruption of another's opinions, beliefs, moral principles, etc.; moral contamination.
7. an influence or impulse passing from one to another and affecting feeling or action.
8. Gram. (in Celtic languages) assimilation in which a vowel is influenced by a following vowel or semivowel; umlaut.
[1350-1400; ME infeccio(u)n < LL infection- (s. of infectio). See INFECT, -ION]

* * *

Invasion of the body by various agents
including bacteria, fungi (see fungus), protozoans, viruses, and worms
and its reaction to them or their toxins.

Infections are called subclinical until they perceptibly affect health, when they become infectious diseases. Infection can be local (e.g., an abscess), confined to one body system (e.g., pneumonia in the lungs), or generalized (e.g., septicemia). Infectious agents can enter the body by inhalation, ingestion, sexual transmission, passage to a fetus during pregnancy or birth, wound contamination, or animal or insect bites. The body responds with an attack on the invader by leukocytes, production of antibodies or antitoxins, and often a rise in temperature. The antibodies may result in short-term or lifelong immunity. Despite significant progress in preventing and treating infectious diseases, they remain a major cause of illness and death, particularly in regions of poor sanitation, poor nutrition, and crowding.

* * *

Universalium. 2010.