Fundamentals of Radiology Practice Test

Pathogens are microorganisms capable of causing disease. This broad category includes viruses, bacteria, fungi, and parasites—any microbe that can initiate illness in a susceptible host qualifies as a pathogen. Not all microbes cause disease; many are harmless or beneficial, so a term like all living organisms is too inclusive. Focusing on the disease-causing potential across different microbes, pathogens is the most accurate descriptor.