関: infectious agents, pathogens

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any disease-producing agent (especially a virus or bacterium or other microorganism)

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病原菌,病原体

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/05/10 07:18:55」(JST)

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A pathogen (Greek: πάθος pathos “suffering, passion” and -γενής -genēs “producer of”) in the oldest and broadest sense is anything that can produce disease.^[1] Typically the term is used to mean an infectious agent (colloquially known as a germ) — a microorganism, in the widest sense such as a virus, bacterium, prion, fungus or protozoan, that causes disease in its host. The host may be an animal, a plant, a fungi or even another microorganism.^[2]^[3]

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 are caused by viral pathogens include 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.

Types of pathogen

Subcellular infectious objects

Prionic

According to the prion theory, prions are infectious pathogens that do not contain nucleic acids. These abnormally folded proteins are found characteristically in some diseases such as scrapie, bovine spongiform encephalopathy (mad cow disease) and Creutzfeldt–Jakob disease.^[4] Although prions fail to meet the requirements laid out by Koch's postulates, the hypothesis of prions as a new class of pathogen led Stanley B. Prusiner to receive the Nobel Prize in Physiology or Medicine in 1997.

Viral

Pathogenic viruses are diseases mainly those of the families of: Adenoviridae, Picornaviridae, Herpesviridae, Hepadnaviridae, Flaviviridae, Retroviridae, Orthomyxoviridae, Paramyxoviridae, Papovaviridae, Polyomavirus, Rhabdoviridae, Togaviridae. Viruses typically range between 20-300 nanometers in length. ^[5]

Prokaryotes

Bacterial

Although the vast majority of bacteria are harmless or beneficial, a few pathogenic bacteria can cause infectious diseases. Bacteria can often be killed by antibiotics because the cell wall on the outside is destroyed, expelling the DNA out of the body of the pathogen, therefore making the pathogen incapable of producing proteins and dies. They typically range between 1 and 5 micrometers in length.

Eukaryotes

Fungal

Fungi comprise a eukaryotic kingdom of microbes that are usually saprophytes (consume dead organisms) but can cause diseases in humans, animals and plants. Fungi are the most common cause of diseases in crops and other plants. The typical fungal spore size is 1-40 micrometer in length.

Other parasites

Some eukaryotic organisms, such as protists and helminths, cause disease.

Treatment and health care

Bacteria are usually treated with antibiotics while viruses are treated with antiviral compounds. Eukaryotic pathogens are typically not susceptible to antibiotics and thus need specific drugs. Infection with many pathogens can be prevented by immunization. A small amount of pathogens are used in vaccines to make immunity stay alert and strengthen defense on the insides to prepare for a larger quantity of the virus ever getting inside. Hygiene is critical for the prevention of infection by pathogens.

Virulence

Virulence (the tendency of a pathogen to cause damage to a host's fitness) evolves when that pathogen can spread from a diseased host, despite that host being very debilitated. 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.

Evolutionary medicine has found that under horizontal transmission, the host population might never develop tolerance to the pathogen.

Transmission

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.

References

^ Dictionary.com: Pathogen. Retrieved August 17, 2013
^ http://www.medterms.com/script/main/art.
^ MetaPathogen - about various types of pathogenic organisms
^ The prion diseases STANLEY B. PRUSINER, Scientific American
^ Viral Special Pathogens Branch | [26] Moved | CDC

External links

Pronunciation Guide to Microorganisms

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English Journal

Development of a novel protein biochip enabling validation of immunological assays and detection of serum IgG and IgM antibodies against Treponema pallidum pathogens in the patients with syphilis.

Huang NL1, Ye L1, Schneider ME2, Du YX2, Xu YH3, Fan LB1, Du WD4.
Biosensors & bioelectronics.Biosens Bioelectron.2016 Jan 15;75:465-71. doi: 10.1016/j.bios.2015.08.036. Epub 2015 Sep 3.
In this study, we developed a novel protein biochip methodology that was characterized by dithiobis (succinimidyl undecanoate) (DSU) and specialized for detection of serum IgG and IgM antibodies against Treponema pallidum pathogens in the patients with syphilis, respectively. The biochips were valid
PMID 26364122

For whom the endocannabinoid tolls: Modulation of innate immune function and implications for psychiatric disorders.

Henry RJ1, Kerr DM2, Finn DP3, Roche M4.
Progress in neuro-psychopharmacology & biological psychiatry.Prog Neuropsychopharmacol Biol Psychiatry.2016 Jan 4;64:167-80. doi: 10.1016/j.pnpbp.2015.03.006. Epub 2015 Mar 17.
Toll-like receptors (TLRs) mediate the innate immune response to pathogens and are critical in the host defence, homeostasis and response to injury. However, uncontrolled and aberrant TLR activation can elicit potent effects on neurotransmission and neurodegenerative cascades and has been proposed t
PMID 25794989

Antimicrobial Peptides and their Pore/Ion Channel Properties in Neutralization of Pathogenic Microbes.

Sharma S, Sahoo N, Bhunia A1.
Current topics in medicinal chemistry.Curr Top Med Chem.2016;16(1):46-53.
The essence of successful antimicrobial chemotherapy lies in selective toxicity of the agent towards the pathogen. An ideal antimicrobial agent should kill pathogens effectively with little or no effect on host cells. There is a dearth of antibiotic and antimicrobial therapies due the rapid developm
PMID 26139119