What are all pathogens considered to be?

Pathogens are specifically defined as microbes that can cause disease in a host. This category includes a variety of organisms, such as viruses, bacteria, fungi, and parasites, that have the potential to disrupt normal bodily functions and lead to illnesses. By understanding that all pathogens are harmful microorganisms, it's clear why the correct answer emphasizes their disease-causing capabilities.

In contrast, some options describe other types of microorganisms or suggest a neutral or beneficial role. Viruses that are harmless do not fit the definition of pathogens, as they do not cause disease. Similarly, bacteria that are commonly present in the human body can be part of the normal flora and may not be harmful in healthy individuals. Lastly, microorganisms found in water can include both pathogens and non-pathogenic organisms, making that option too broad and not accurate for classifying all pathogens. The focus on the disease-causing nature of pathogens is what solidifies the choice as correct.