What is a pathogen?

A pathogen is specifically defined as an infectious agent capable of causing disease in a host. This can include various types of microorganisms such as bacteria, viruses, fungi, and parasites. The fundamental characteristic that distinguishes a pathogen is its ability to invade a living organism and provoke an immune response that often leads to illness.

The other options do not accurately capture the essence of what a pathogen is. For example, a non-infectious agent does not cause disease, and therefore cannot be classified as a pathogen. Similarly, a treatment protocol for infections refers to treatments designed to combat pathogens rather than being a pathogen itself. An environmental health hazard encompasses a broader range of factors that can affect health, which may or may not include pathogens specifically. Hence, the focus on the infectious nature and disease-causing potential solidifies why the correct identification of a pathogen is as an infectious agent capable of causing disease.