- any disease-producing agent, especially a virus, bacterium, or other microorganism.
- any agent that can cause disease
n.1880, a back-formation from pathogenic. n.
- An agent that causes disease, especially a living microorganism such as a bacterium, virus, or fungus.
- An agent that causes infection or disease, especially a microorganism, such as a bacterium or protozoan, or a virus. See Note at germ.
A disease-causing agent. Microorganisms, viruses, and toxins are examples of pathogens.