(pathology, immunology) 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.
2013-01, Katie L. Burke, Ecological Dependency, In his first book since the 2008 essay collection Natural Acts: A Sidelong View of Science and Nature, David Quammen looks at the natural world from yet another angle: the search for the next human pandemic, what epidemiologists call “the next big one.†His quest leads him around the world to study a variety of suspect zoonoses—animal-hosted pathogens that infect humans.
