What is the definition of a pathogen?

A pathogen is defined as an organism that causes disease in its host. This includes a variety of microorganisms such as bacteria, viruses, fungi, and protozoa that can invade a host's body and disrupt normal physiological functions, leading to illness or disease. Pathogens can exploit the host's resources, evade the immune response, and induce harmful effects, which are key characteristics of their pathogenicity.

Understanding this definition is crucial for recognizing how diseases spread and how to anticipate their effects on health. The term encompasses a wide range of infectious agents, each with unique mechanisms of causing disease. By identifying a microorganism as a pathogen, health professionals can better determine appropriate prevention strategies, treatments, and public health measures to mitigate the spread of infectious diseases.