What is the definition of a pathogen?

A pathogen is defined as a disease-causing organism. This includes a variety of microorganisms such as bacteria, viruses, fungi, and parasites that can lead to illness or disease in their hosts. Pathogens can invade the body, multiply, and disrupt normal physiological functions, thereby leading to a range of health issues, from mild infections to serious diseases. Understanding this definition is crucial in the context of health care and infection control practices, as it helps in recognizing how diseases can be transmitted and what measures need to be taken to prevent outbreaks and manage patient care effectively.

The other options do not align with the accepted definition of a pathogen. For instance, a harmless organism would not cause disease and is therefore not relevant when describing pathogens. An immune response refers to the body’s defense mechanism that works to combat pathogens, but it is not an organism itself. A human cell is a fundamental unit of life but does not inherently cause disease, differentiating it from the concept of a pathogen.