Pathogen

pathogenspathogenicpathogenicityinfectious agentinfectious agentsgermsgermdisease-causing organismsinfectious organismpathogenic organisms
In biology, a pathogen (πάθος pathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease.wikipedia
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Disease

morbidityillnessdiseases
In biology, a pathogen (πάθος pathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease.
A disease may be caused by external factors such as pathogens or by internal dysfunctions.

Virus

virusesviralvirion
Typically, the term is used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus.
A virus is a small infectious agent that replicates only inside the living cells of an organism.

Germ theory of disease

germ theorygermsbacteriological revolution
A pathogen may also be referred to as an infectious agent, or simply a germ.
It states that microorganisms known as pathogens or "germs" can lead to disease.

Microorganism

microorganismsmicrobemicrobes
Typically, the term is used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus.
They are the pathogens responsible for many infectious diseases and as such are the target of hygiene measures.

Virulence

virulentavirulenceavirulent
Pathogenicity is related to virulence in meaning, but some authorities have come to distinguish it as a qualitative term, whereas the latter is quantitative.
The pathogenicity of an organism - its ability to cause disease - is determined by its virulence factors.

Opportunistic infection

opportunistic pathogenopportunisticopportunistic pathogens
A bacterium may participate in opportunistic infections in immunocompromised hosts, acquire virulence factors by plasmid infection, become transferred to a different site within the host, or respond to changes in the overall numbers of other bacteria present.
An opportunistic infection is an infection caused by pathogens (bacteria, viruses, fungi, or protozoa) that take advantage of an opportunity not normally available, such as a host with a weakened immune system, an altered microbiota (such as a disrupted gut microbiota), or breached integumentary barriers.

Prion

prionsprion diseasePrion diseases
Typically, the term is used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus.
Empirical results of ionizing doses applied to the unknown infectious substance evidenced an infectious particle size too small to be a viral mechanism.) In his paper, entitled "Self-replication and Scrapie", Griffith proposed three ways in which a protein could be a pathogen.

Lactobacillus

lactobacilliDöderlein vaginal bacilluslactic acid bacteria
For example, infection of mesenteric lymph glands of mice with Yersinia can clear the way for continuing infection of these sites by Lactobacillus, possibly by a mechanism of "immunological scarring".
Lactobacillus exhibits a mutualistic relationship with the human body, as it protects the host against potential invasions by pathogens, and in turn, the host provides a source of nutrients.

Vertically transmitted infection

vertical transmissionmother-to-child transmissionvertically
Horizontal transmission occurs between hosts of the same species, in contrast to vertical transmission, which tends to evolve symbiosis (after a period of high morbidity and mortality in the population) by linking the pathogen's evolutionary success to the evolutionary success of the host organism.
A vertically transmitted infection is an infection caused by pathogens (such as bacteria and viruses) that use mother-to-child transmission, that is, transmission directly from the mother to an embryo, fetus, or baby during pregnancy or childbirth.

Parasitism

parasiteparasiticparasites
However, these animals are usually, in common parlance, referred to as parasites rather than pathogens.
These parasites are microorganisms, namely protozoa, bacteria, or viruses, often intracellular pathogens (causing disease).

Bacteria

bacteriumbacterialEubacteria
Typically, the term is used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus.
These differences in structure can produce differences in antibiotic susceptibility; for instance, vancomycin can kill only gram-positive bacteria and is ineffective against gram-negative pathogens, such as Haemophilus influenzae or Pseudomonas aeruginosa.

Fecal–oral route

fecal-oral routefecal-oralfaecal-oral route
Transmission of pathogens occurs through many different routes, including airborne, direct or indirect contact, sexual contact, through blood, breast milk, or other body fluids, and through the fecal-oral route.
The fecal–oral route (also called the oral–fecal route or orofecal route) describes a particular route of transmission of a disease wherein pathogens in fecal particles pass from one person to the mouth of another person.

Toxin

toxinstoxicbiotoxin
A pathogen may be described in terms of its ability to produce toxins, enter tissue, colonize, hijack nutrients, and its ability to immunosuppress the host.
Toxins produced by microorganisms are important virulence determinants responsible for microbial pathogenicity and/or evasion of the host immune response.

Optimal virulence

the host population might never develop tolerance to the pathogendecreasing virulencevirulence versus transmissibility
Evolutionary medicine has found that under horizontal transmission, the host population might never develop tolerance to the pathogen.[citation needed]
A pathogen that is too restrained will lose out in competition to a more aggressive strain that diverts more host resources to its own reproduction.

Pathogenic bacteria

bacterial infectionbacterial infectionsbacterial
However, a relatively small list of pathogenic bacteria can cause infectious diseases.
Although most bacteria are harmless or often beneficial, some are pathogenic, with the number of species estimated as fewer than a hundred that are seen to cause infectious diseases in humans.

Plasmid

plasmidsepisomeplasmid vector
A bacterium may participate in opportunistic infections in immunocompromised hosts, acquire virulence factors by plasmid infection, become transferred to a different site within the host, or respond to changes in the overall numbers of other bacteria present.

Mycobacterium tuberculosis

M. tuberculosistubercle bacillusMycobacterium
One of the bacterial diseases with the highest disease burden is tuberculosis, caused by the bacterium Mycobacterium tuberculosis, which killed 1.5 million people in 2013, mostly in sub-Saharan Africa.
tb) is a species of pathogenic bacteria in the family Mycobacteriaceae and the causative agent of tuberculosis.

Foodborne illness

food poisoningptomaineptomaine poisoning
Pathogenic bacteria contribute to other globally significant diseases, such as pneumonia, which can be caused by bacteria such as Streptococcus and Pseudomonas, and foodborne illnesses, which can be caused by bacteria such as Shigella, Campylobacter, and Salmonella.
Foodborne illness (also foodborne disease and colloquially referred to as food poisoning) is any illness resulting from the spoilage of contaminated food, pathogenic bacteria, viruses, or parasites that contaminate food, as well as toxins such as poisonous mushrooms and various species of beans that have not been boiled for at least 10 minutes.

Creutzfeldt–Jakob disease

Creutzfeldt-Jakob diseaseCJDcreutzfeldt-jakob syndrome
These abnormally folded proteins are found characteristically in some diseases such as scrapie, bovine spongiform encephalopathy (mad cow disease) and Creutzfeldt–Jakob disease.
Prions, the infectious agent of CJD, may not be inactivated by means of routine surgical instrument sterilization procedures.

Campylobacter

campylobacter infectionsCampylobacter jejuni
Pathogenic bacteria contribute to other globally significant diseases, such as pneumonia, which can be caused by bacteria such as Streptococcus and Pseudomonas, and foodborne illnesses, which can be caused by bacteria such as Shigella, Campylobacter, and Salmonella.
Most Campylobacter species can infect humans and other animals, causing disease.

Koch's postulates

Koch’s postulatesKoch's postulatepostulates
Koch's postulates)''.
Koch's postulates were developed in the 19th century as general guidelines to identify pathogens that could be isolated with the techniques of the day.

Candida albicans

C. albicansCandidayeast
There are approximately 300 known fungi that are pathogenic to humans including Candida albicans, which is the most common cause of thrush, and Cryptococcus neoformans, which can cause a severe form of meningitis.
It is usually a commensal organism, but it can become pathogenic in immunocompromised individuals under a variety of conditions.

Tuberculosis

consumptionpulmonary tuberculosisTB
One of the bacterial diseases with the highest disease burden is tuberculosis, caused by the bacterium Mycobacterium tuberculosis, which killed 1.5 million people in 2013, mostly in sub-Saharan Africa.
The high lipid content of this pathogen accounts for many of its unique clinical characteristics.

Papaya ringspot virus

Papaya ringspotringspotringspot virus
Notable plant viruses include the Papaya ringspot virus which has caused millions of dollars of damage to farmers in Hawaii and Southeast Asia, and the Tobacco mosaic virus which caused scientist Martinus Beijerinck to coin the term "virus" in 1898.
Papaya ringspot virus (PRSV) is a pathogenic plant virus in the genus Potyvirus and the virus family Potyviridae which primarily infects the papaya tree.

Plant pathology

plant pathogenplant pathologistPhytopathology
Bacterial plant pathogens are also a serious problem causing leaf spots, blights, and rots in many plant species.
Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors).