The abnormal invasion of a host tissue by organisms such as bacteria, viruses, or parasites, with or without signs and symptoms of disease is called what?

• A. Infection
• B. Inflammation
• C. Contamination
• D. Infestation

Answer: (A)

Infection means invasion of body tissues by microorganisms such as bacteria, viruses, or parasites, and it may or may not involve multiplication or produce symptoms. The organisms have entered and established themselves in the tissue, which is why this term fits even when a person shows no signs of illness (asymptomatic infection) or has mild or severe disease. Inflammation, by contrast, is the body's defensive response to injury or infection, not the invasion itself. Contamination is simply the presence of organisms on a surface or object without tissue invasion or disease, and infestation refers to parasites living on or in a host (usually larger organisms like lice or mites), not the general invasion of tissues by microbes.