imported>Justin Yang |
imported>John Stephenson |
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| A '''pathogen''' is the organism that causes an [[infectious disease]]. It may be a [[bacterium]], [[protozoa]]n, [[fungus]], etc. Another way to phrase this is that '''pathogenic organisms''' are disease-producing. | | A '''pathogen''' is the organism that causes an [[infectious disease]]. It may be a [[bacterium]], [[protozoa]]n, [[fungus]], etc. Another way to phrase this is that '''pathogenic organisms''' are disease-producing. |
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| A '''pathogen''' ({{lang-el|πάθος}} ''pathos'', "suffering, passion" and γἰγνομαι (γεν-) ''gignomai'' (gen-) "I give birth to") or '''infectious agent''' — colloquially, a '''germ''' — is a [[microbe]] or [[microorganism]] such as a [[virus]], [[bacterium]], [[prion]], or [[fungus]] that causes [[disease]] in its [[animal]] or [[plant]] [[Host (biology)|host]].<ref>http://www.medterms.com/script/main/art.</ref><ref>http://www.metapathogen.com</ref> 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.
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| The body contains many natural orders of defense against some of the common pathogens (such as ''[[Pneumocystis]]'') in the form of the human [[immune system]] and by some "helpful" [[bacteria]] present in the human body's [[Human flora|normal flora]]. However, if the immune system or "good" bacteria is damaged in any way (such as by [[chemotherapy]], [[HIV|human immunodeficiency virus]] (HIV), or [[antibiotic]]s being taken to kill other pathogens), pathogenic [[bacteria]] that were being held at bay can proliferate and cause harm to the host. Such cases are called [[opportunistic infection]].
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| Some pathogens (such as the bacterium ''[[Yersinia pestis]]'' which may have caused the [[Black Plague]], the ''[[Variola]]'' virus, and the [[Malaria]] protozoa) have been responsible for massive numbers of casualties and have had numerous effects on afflicted groups. Of particular note in modern times is HIV, which is known to have infected several million humans globally, along with the [[Influenza]] virus. Today, while many medical advances have been made to safeguard against infection by pathogens, through the use of [[vaccination]], [[antibiotics]], and [[fungicide]], pathogens continue to threaten human life. Social advances such as [[food safety]], [[hygiene]], and [[water treatment]] have reduced the threat from some pathogens.
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| Not all pathogens are negative. In [[entomology]], pathogens are one of the "Three P's" ([[predator]]s, pathogens, and [[parasitoids]]) that serve as natural or introduced [[biological control]]s to suppress [[arthropod]] [[Pest (organism)|pest]] populations.
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| ==Types of pathogen==
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| ===Viral===
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| {{See|Virus disease}}
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| Pathogenic viruses are mainly those of the families of: [[Adenoviridae]], [[Picornaviridae]], [[Herpesviridae]], [[Hepadnaviridae]], [[Flaviviridae]], [[Retroviridae]], [[Orthomyxoviridae]], [[Paramyxoviridae]], [[Papovaviridae]], [[Polyomavirus]], [[Rhabdoviridae]], [[Togaviridae]]. Some notable pathogenic viruses cause: smallpox, influenza, mumps, measles, [[chickenpox]], ebola, and rubella. Viruses typically range between 20-300 nanometers in length.
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| ===Bacterial===
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| {{Main|Pathogenic bacteria}}
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| Although the vast majority of bacteria are harmless or beneficial, a few pathogenic bacteria can cause infectious diseases. The most common bacterial disease is [[tuberculosis]], caused by the bacterium ''[[Mycobacterium tuberculosis]]'', which affects about 2 million people mostly in sub-Saharan Africa. Pathogenic bacteria contribute to other globally important 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]]''. Pathogenic bacteria also cause infections such as [[tetanus]], [[typhoid fever]], [[diphtheria]], [[syphilis]] and [[Hansen's disease]]. Bacteria can often be killed by antibiotics because the cell wall in the outside is destroyed and then the DNA. They typically range between 1-5 micrometers in length.
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| ===Fungal===
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| Fungi comprise a eukaryotic kingdom of microbes that are usually [[Saprophyte|saprophytes]] but can cause diseases in humans, animals and plants. Fungi are the most common cause of diseases in crops and other plants. Life threatening fungal infections in humans most often occur in immunocompromised patients or vulnerable people with a weakened immune system, although fungi are common problems in the immunocompetent population as the causative agents of skin, nail or yeast infections. Most antibiotics that function on bacterial pathogens cannot be used to treat fungal infections because fungi and their hosts both have eukaryotic cells. Most clinical fungicides belong to the [[Azole|azole group]]. The typical fungal spore size is 1-40 micrometer in length.
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| ===Other parasites===
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| {{main|Human parasites}}
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| Some eukaryotic organisms, such as [[protists]] and [[helminths]], cause disease. One of the best known diseases caused by protists in the genus ''[[Plasmodium]]'' is [[malaria]]. These can range from 3-200 micrometers in length.
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| ===Prionic===
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| {{Main|Prion}}
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| Prions are infectious pathogens that do not contain [[nucleic acid]]s. Prions are abnormal proteins whose presence causes some diseases such as [[scrapie]], [[bovine spongiform encephalopathy]] (mad cow disease) and [[Creutzfeldt–Jakob disease]].<ref>[http://www.mad-cow.org/~tom/prionSP.html ''The prion diseases''] STANLEY B. PRUSINER, Scientific American</ref> The discovery of prion as a new class of pathogen led [[Stanley B. Prusiner]] to receive the [[Nobel Prize in Physiology or Medicine]] in [[1997]].
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| ==Potency==
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| One hypothesis regarding pathogens states that the longer a pathogen can survive outside of the body, the more dangerous it can be to a potential host.{{citation needed|date=March 2009}} For example, the [[smallpox virus]] (''variola virus'') can survive outside the human body for approximately 885 days. It is also one of the most deadly pathogenic viruses, as it kills between 20-50% of the people it infects. The tuberculosis bacterium kills 1 in 5 of the people it infects, but only survives 244 days outside of its host. However, research into the basis of the ability of pathogens to cause disease provides evidence from multiple and diverse species of the existence of pathogenicity or virulence factors, encoded within the pathogens' genetic material, that facilitate microbes to cause disease.
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| In countries that have higher sanitation standards, pathogens cannot survive for as long outside of the human. This is seen as encouragement to mutations to the pathogen which would make it less deadly, as such mutations would allow the pathogen to survive in the host for longer periods of time.{{citation needed|date=March 2009}}
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| ==Transmission==
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| {{main|Transmission (medicine)}}
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| One of the primary pathways by which food or water become contaminated is from the release of untreated sewage into a [[drinking water]] supply or onto cropland, with the result that people who eat or drink contaminated sources become infected. In [[developing countries]] most sewage is discharged into the environment or on cropland; even in [[developed countries]] there are periodic system failures resulting in a [[sanitary sewer overflow]].
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| ==Examples of pathogens==
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| ===Major human pathogens===
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| *''[[Bacillus anthracis]]'' — the causative agent of [[anthrax]] in humans and animals.
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| *''[[Clostridium botulinum]]'' — releases the most powerful [[neurotoxin]] leading to death from [[botulism]].
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| * ''[[Mycobacterium tuberculosis]]'' — the causative agent of most cases of [[tuberculosis]]
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| * ''[[Mycobacterium leprae]]'' — the bacterium that causes [[leprosy]] (Hansen's disease)
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| * ''[[Yersinia pestis]]'' — [[pneumonic plague|pneumonic]], [[septicemic plague|septicemic]], and the notorious [[bubonic plague|bubonic]] plagues (aka "[[Black Death]]")
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| * ''[[Rickettsia prowazekii]]'' — the etiologic agent of [[epidemic typhus|typhus fever]]
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| * ''[[Bartonella]]'' spp.
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| * [[Spanish influenza]] virus
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| ==See also==
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| * [[Ecological competence]]
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| * [[Emerging Pathogens Institute]]
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| ==References==
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| {{reflist}}
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| ==External links==
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| *[http://microvet.arizona.edu/Courses/MIC419/Tutorials/infectiousdisease.html Infectious Disease -- University of Arizona (microvet.arizona.edu)]
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| *[http://www.d.umn.edu/~rhicks1/diversity/Pronunciation%20Guide.pdf Pronunciation Guide to Microorganisms]
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| {{Infectious_disease}}
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| [[Category:Microbiology]]
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| [[af:Patogeen]]
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| [[am:ጀርም]]
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| [[ar:ممراض]]
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| [[bs:Patogen]]
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| [[ca:Patogen]]
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| [[cs:Patogen]]
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| [[cy:Pathogen]]
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| [[da:Patogen]]
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| [[de:Krankheitserreger]]
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| [[et:Patogeen]]
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| [[es:Agente biológico patógeno]]
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| [[eo:Infekta agento]]
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| [[eu:Patogeno]]
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| [[fa:بیمارگر]]
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| [[fr:Agent infectieux]]
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| [[ga:Pataigin]]
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| [[gl:Axente biolóxico patóxeno]]
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| [[ko:병원체]]
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| [[id:Patogen]]
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| [[is:Sýkill]]
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| [[it:Microrganismo patogeno]]
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| [[he:פתוגניות]]
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| [[kn:ರೋಗಾಣು]]
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| [[ht:Patojèn]]
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| [[lv:Patogēns]]
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| [[lt:Patogenas]]
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| [[hu:Kórokozó]]
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| [[nl:Pathogeen]]
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| [[ja:病原体]]
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| [[no:Patogen]]
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| [[pl:Patogen]]
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| [[pt:Agente patogénico]]
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| [[ro:Agent patogen]]
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| [[qu:Unquchiq]]
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| [[ru:Патоген]]
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| [[simple:Pathogen]]
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| [[sk:Patogén]]
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| [[sl:Patogen]]
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| [[sr:Patogen]]
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| [[su:Kuman]]
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| [[sv:Smittämne]]
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| [[ta:நோய்க்காரணி]]
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| [[tr:Patojen]]
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| [[uk:Патоген]]
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| [[ur:ممراض]]
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| [[zh:病原]]
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