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In biology, a pathogen (Greek: πάθος, pathos "suffering", "passion" and -γενής, -genēs "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. [1] The term pathogen came into use in the 1880s.
Study of obligate pathogens is difficult because they cannot usually be reproduced outside the host. However, in 2009 scientists reported a technique allowing the Q-fever pathogen Coxiella burnetii to grow in an axenic culture and suggested the technique may be useful for study of other pathogens.
Diseases caused by facultative intracellular bacteria include Listeriosis (Listeria monocytogenes), Typhoid Fever (Salmonella typhi), Legionnaires' disease (Legionella pneumophila), and Salmonellosis (Salmonella enterica) to name a few. [3] While they can invade the human body, they are also capable of living extracellularly.
This is where the name opportunistic pathogen comes from: they are only pathogens when the opportunity to infect the host is there. An example of an opportunistic pathogen is Candida albicans . Candida albicans is a type of fungus/yeast found in the intestines and mucous membranes (like the vagina and throat) of healthy humans.
The following outline is provided as an overview of and topical guide to concepts related to infectious diseases in humans.. Infection – transmission, entry/invasion after evading/overcoming defense, establishment, and replication of disease-causing microscopic organisms (pathogens) inside a host organism, and the reaction of host tissues to them and to the toxins they produce.
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. [1] An infectious disease, also known as a transmissible disease or communicable disease, is an illness resulting from an infection.
Once pathogens attach to host cells, they can cause direct damage as the pathogens use the host cell for nutrients and produce waste products. [23] For example, Streptococcus mutans, a component of dental plaque, metabolizes dietary sugar and produces acid as a waste product. The acid decalcifies the tooth surface to cause dental caries. [24]
The host-pathogen interaction is defined as how microbes or viruses sustain themselves within host organisms on a molecular, cellular, organismal or population level. This term is most commonly used to refer to disease-causing microorganisms although they may not cause illness in all hosts. [ 1 ]