What is a pathogen?

A pathogen is defined as a microorganism that can cause disease in a host. This includes various types of organisms, such as bacteria, viruses, fungi, and parasites. Pathogens invade the host's body, evade the immune system, and can lead to illness by disrupting normal physiological processes. Understanding what constitutes a pathogen is crucial for public health, as it guides the development of sanitation practices, disease control measures, and healthcare strategies.

The other choices do not accurately describe a pathogen. For instance, a living organism is a much broader term that encompasses all forms of life, including those that are harmless or beneficial to humans. A natural habitat for viruses refers to the environments where viruses thrive, which is unrelated to their capacity to cause disease. Lastly, a method of disease prevention involves strategies or practices to avert the spread or onset of disease, rather than defining the organisms themselves that instigate these conditions. This highlights the significance of correctly identifying and understanding pathogens in the field of environmental health and disease prevention.