What are disease-causing microorganisms commonly referred to as?

The term "pathogens" is used to refer to disease-causing microorganisms collectively. This term encompasses a wide range of organisms that can lead to illness in hosts, including not only viruses and bacteria but also fungi, parasites, and prions. It highlights the capability of these microorganisms to cause disease, which can affect various systems within the body.

While the other choices identify specific types of pathogens, they do not encompass the full range of microorganisms known to cause diseases. For example, viruses and bacteria are individual categories within the larger classification of pathogens. "Infectious agents" is a broader term that can encompass pathogens, but it is not as commonly used in everyday language as "pathogens" to specifically denote those microorganisms that cause disease. Therefore, the term "pathogens" is the most precise choice when referring to microorganisms that lead to health issues.