What is the term for an organism that causes disease?

The term for an organism that causes disease is a pathogen. Pathogens encompass a variety of infectious agents, including bacteria, viruses, fungi, and parasites, that can lead to illness in a host organism. The ability to cause disease distinguishes pathogens from other microbes, which may be harmless or even beneficial to human health.

Understanding the role of pathogens in infectious diseases is critical in medical terminology and healthcare practice. For example, differentiating between a pathogen and a microbe highlights that not all microbes induce diseases; many are essential for normal body functions, such as those found in the gut microbiome. Infection refers to the process or state of being infected by a pathogen but does not specifically identify the organism itself. An antigen is a substance that the immune system recognizes as foreign and may trigger an immune response, but it is not the organism causing the disease. Thus, recognizing pathogens is fundamental to diagnosing and treating infectious diseases effectively.