pathogen(noun)

any disease-producing agent (especially a virus or bacterium or other microorganism)

pathogen(Noun)

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.

pathogen

A disease producing microorganism that directly attacks human tissue and biological processes.