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/ˈpaTHəjən/  /-ˌjen/

Noun, pl. pathogens

1. An infectious agent (colloquially known as a germ); a microorganism—in the widest sense, such as a virus, bacterium, prion, or fungus—that causes disease in its host. The host may be an animal (including humans), a plant, or even another microorganism. (

2. Any organism or substance, especially a microorganism, capable of causing disease, such as bacteria, viruses, protozoa or fungi. Microorganisms are not considered to be pathogenic until they have reached a population size that is large enough to cause disease. (

3. A specific causative agent (as a bacterium or virus) of disease. (

4. An agent causing disease or illness to its host, such as an organism or infectious particle capable of producing a disease in another organism. (

Syn: infectious agent, germ

Word origin: From Greek pathos, “suffering,emotion” + gene, “to give birth to.”

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