A pathogen (Greek: πάθος pathos “suffering, passion” and γενής
genēs “producer of”) or infectious agent (colloquially known as
a germ) is 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. There are several substrates including
pathways whereby pathogens can invade a host. The principal
pathways have different episodic time frames, but soil
contamination has the longest or most persistent potential for
harboring a pathogen. Diseases caused by organisms in humans are
known as pathogenic diseases. Some of the diseases that a
pathogen can cause are smallpox, influenza, mumps, measles,
chickenpox, ebola and rubella. Not all pathogens are necessarily
undesirable to humans. In entomology, pathogens are one of the
"Three P's" (predators, pathogens and parasitoids) that serve as
natural or introduced biological controls to suppress arthropod
pest populations. Pathogenic