What is the term for a disease-causing organism?

• A. Germ
• B. Microbe
• C. Infection agent
• D. Pathogen

Answer: (D)

A disease-causing organism is called a pathogen. This term specifically signals the ability to cause illness in a host, and it covers the main types of disease agents—viruses, bacteria, fungi, and parasites. Microbes is a broader umbrella that includes all microscopic organisms, many of which are harmless or beneficial, not necessarily disease-causing. Germ is a informal common-use word that doesn’t carry precise scientific meaning. An infection agent is a descriptive phrase, but not the standard clinical term. Because only some microbes have the capacity to overcome a host’s defenses and produce symptoms, the precise word pathogen is used to identify those disease-causing organisms, such as the influenza virus or pathogenic strains of bacteria.