What do viruses and microorganisms that can cause disease classify as?

Viruses and microorganisms that cause disease are classified as pathogens. This term specifically refers to any organism, including bacteria, viruses, fungi, or parasites, that is capable of causing illness or disease in a host. Pathogens can invade the body, multiply, and disrupt normal biological functions, leading to infections or other health issues.

The other terms listed do not accurately represent the nature of agents that cause disease. Infectants refer more broadly to agents that can introduce infection but may not inherently imply disease-causing capability. Contaminants typically describe substances that pollute or contaminate but are not specifically linked to disease. Allergens are substances that can trigger allergic reactions, which is a different mechanism compared to pathogen-induced illnesses. This context highlights why the correct classification of viruses and disease-causing microorganisms is as pathogens.