«In biology, a pathogen (Greek: πάθοςpathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.
The term pathogen came into use in the 1880s. Typically, the term is used to describe an infectiousmicroorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus. Small animals, such as certain kinds of worms and insect larvae, can also produce disease. However, these animals are usually, in common parlance, referred to as parasites rather than pathogens. The scientific study of microscopic organisms, including microscopic pathogenic organisms, is called microbiology, while the study of disease that may include these pathogens is called pathology. Parasitology, meanwhile, is the scientific study of parasites and the organisms that host them.» (wikipedia)