What best describes an infectious disease?

• A. Disease caused by pathogenic microorganisms that enter the body. An infectious disease may or may not be spread from one person to another person
• B. A chronic disease caused by genetics
• C. A disease caused by non-pathogenic microorganisms
• D. A disease that only affects the skin

Answer: (A)

An infectious disease results from pathogenic microorganisms such as bacteria, viruses, fungi, or parasites invading the body. These diseases may be transmitted from one person to another, but not all infectious diseases spread person-to-person; some are contracted from contaminated food, water, soil, or via vectors. The key point is that a disease is caused by a pathogenic organism and has the potential for transmission in some way. The other descriptions aren’t correct: a chronic genetic disease isn’t caused by pathogens; a disease caused by non-pathogenic microorganisms wouldn’t be infectious; and a disease that affects only the skin isn't a defining feature of infectiousness, since infectious diseases can involve many body systems and transmission patterns.