Which statement best defines Infectious Disease?

• A. Any illness caused by a specific micro-organism
• B. An illness that cannot be transmitted
• C. A disease caused by genetics
• D. A disease caused by environmental factors

Answer: (A)

Infectious disease is defined by being caused by a microorganism such as bacteria, viruses, fungi, or parasites, and these illnesses are typically capable of transmission through contact, vectors, or the environment. The best description here captures that idea: it’s any illness caused by a microorganism. That framing centers on the role of a pathogenic agent, which is what makes an illness infectious. The other statements describe non-infectious causes—genetic factors or environmental factors—or claim non-transmission, which doesn’t fit the infectious category.