Germ theory

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'''Germ theory''' is the [[theory (science)|theory]] that microscopic organisms ([[bacteria]], [[virus]]es, [[fungi]], or certain protozoa, as well as a few very weird things like free-living [[prion]]s and [[cancer]] cells) cause many infectious diseases.<ref name="SAGEPubMattingly">{{Cite book |last=Mattingly |first=James |url=https://books.google.com/books?id=wptjEAAAQBAJ&pg=PA334#v=onepage&q&f=false|title=The SAGE Encyclopedia of Theory in Science, Technology, Engineering, and Mathematics |date=2022-09-21 |publisher=SAGE Publications |isbn=978-1-4833-4771-4 |pages=331–335 |language=en}}</ref> The idea that minuscule creatures can cause disease (also called an ''animacular hypothesis'' or ''animacular theory'') was proposed as early as ancient Roman and late medieval times.<ref>{{Cite journal |last=Allen |first=Phyllis |date=1947 |title=Early American Animalcular Hypotheses |url=https://www.jstor.org/stable/44441190 |journal=Bulletin of the History of Medicine |volume=21 |issue=5 |pages=734–743 |issn=0007-5140}}</ref><ref name="HarvardLibrary">{{Cite web |title=Historical Views of Diseases and Epidemics: Germ Theory |url=https://curiosity.lib.harvard.edu/contagion/feature/germ-theory |url-status=live |website=Harvard Library}}</ref> Later confirmed and popularized in the 19th century by French biologist [[Louis Pasteur]] and others, germ theory is one of the most well-established principles in medicine and epidemiology, as well as a cornerstone for public sanitation policy. Incredibly, despite a mountain of evidence that would make [[evolution]] look like a statistical glitch, it still has its [[denialism|deniers]], many of whom portray Pasteur as an outright fraud. Such people, curiously, will seldom offer to take an injection of [[HIV]] or a shot glass of salmonella to prove their thesis.

==Basics==
Germ theory states that microorganisms can and often do cause disease.<ref name="SAGEPubMattingly"/> The often referred-to [[Koch's postulates]] are one method that demonstrates the relationship between a microorganism and a disease, but they are not always dispositive.

==History==
Humans have explored the causes of disease transmission since written records existed. [[Herodotus]] discussed the origins of [[smallpox]]. Hippocrates studied many infectious diseases, and described them quite accurately. Marcus Terentius Varro even wrote in the year 36 BC that diseases could be caused by "certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose".<ref name="Gorski2021">Gorski, David [https://sciencebasedmedicine.org/germ-theory-denial-in-the-age-of-the-covid-19-pandemic/ "Germ theory denial in the age of the COVID-19 pandemic"]. [[Science-Based Medicine]], January 4, 2021.</ref><ref>{{cite book | vauthors = Varro MT, Storr-Best L | title = Varro on Farming | location = London, England | publisher = G. Bell and Sons, Ltd. | date = 1912 | volume = Book 1 | url = https://archive.org/stream/onfarmingmterent00varruoft#page/38/mode/2up/search/diseases | page = 9 }}</ref> He and his contemporaries obviously had no way to seriously verify germ theory,{{efn|Although, ancient Romans did create devices to magnify vision, which is impressive, but they wouldn't have been near enough to view disease-causing viruses or bacteria with.}} however, and this was essentially just an educated guess that happened to be correct. But by 1676, Antonie van Leeuwenhoek had verified by microscope the existence of certain microorganisms such as protozoa and bacteria.<ref>{{Cite book |last=Robertson |first=Lesley |url=https://books.google.com/books?id=qiYiDAAAQBAJ&newbks=0 |title=Antoni van Leeuwenhoek: Master of the Minuscule |last2=Backer |first2=Jantien |last3=Biemans |first3=Claud |last4=Doorn |first4=Joop van |last5=Krab |first5=Klaas |last6=Reijnders |first6=Willem |date=2016-05-09 |publisher=Brill |isbn=978-90-04-30430-7 |pages=81 |language=en}}</ref><ref name="SAGEPubMattingly"/> So, with the invention of powerful enough microscopes, the rubric for verifying a germ theory of disease began to take shape.

More prominent early theories focused on ''miasmas'' (some force that apparently could only be observed by its effects on people, thought to be carried invisibly in air or water), ''[[Heroic medicine|humoral imbalance]]'' (the assumption that four vital substances existed in the body and an imbalance of them caused disease), and other speculative ideas.<ref name="SAGEPubMattingly"/> Do note that despite these ideas appearing ''quaint'' or ''preposterous'' in our more enlightened times, these concepts were based on ''real observation'' and taken very seriously. Even if flawed, these concepts are the [[Protoscience|precursor to modern science]] in that they were honest attempts to learn and build a foundation for saving lives. Miasma theory proponents sparked reforms such as those advanced by the {{wpl|sanitary movement}}, improving public health.<ref>{{Cite news |last=Gainty |first=Caitjan |date=July 5, 2021 |title=Germ theory denialism is alive and well – and taking the nuance out of scientific debate |work=The Conversation |url=https://theconversation.com/germ-theory-denialism-is-alive-and-well-and-taking-the-nuance-out-of-scientific-debate-163408 |access-date=January 20, 2023}}</ref> Still, actual progress in empirically validating germ theory wouldn't take place until the 18th and 19th centuries.

In the 19th century, [[Ignaz Semmelweis]] made seminal observations on childbed fever (puerperal fever), noting that in situations where doctors washed their hands between procedures, the incidence of sepsis among delivering mothers dropped off drastically. Other researchers, such as {{wpl|Theodor Billroth}} (discovery of streptococci in pus), [[Louis Pasteur|Pasteur]] (discovery of strep in the blood of a septic woman), and [[Joseph Lister]] (pioneer of antisepsis in surgery) cemented the germ theory of disease as one of the foundations of modern science.<ref name="SAGEPubMattingly"/>

The strongest opposition to germ theory (more specifically, microscopic life giving rise to macroscopic life and disease) was "spontaneous generation" or [[abiogenesis]], the concept that life needed no precursor and literally spawned from nothing or from inert material.<ref name="SAGEPubMattingly"/> Actual microbial life was very certain and undeniable at this time by all but the most stubborn researchers. Abiogenesis suggested a great obstacle to transmission of disease (though never truly made clear as to how) from person to person.

An early theory involving microbes was published by Athanasius Kircher in 1658: he observed blood infected by bubonic plague through a microscope, describing the "little worms" he saw. He supposed that rotting material caused universally present eggs for these invisible creatures to hatch. His experiments inspired later reviews of the matter by Francesco Redi which challenged Kircher's ideas supportive of spontaneous generation.<ref name="HarvardLibrary"/><ref>{{Cite news |last=Glassie |first=John |date=April 22, 2020 |title="Invisible Little Worms": Athanasius Kircher's Study of the Plague |work=The Public Domain Review |url=https://publicdomainreview.org/essay/athanasius-kircher-study-of-the-plague}}</ref><ref>{{Cite news |last=Findlen |first=Paula |title=Microscopic Musings: Athanasius Kircher and the Roman Plague of 1656–57 |work=Harvard Library Bulletin |url=https://harvardlibrarybulletin.org/microscopic-musings-athanasius-kircher-and-roman-plague}}</ref>

Disproving abiogenesis took many people and experiments but it is Robert Koch who is generally regarded as disproving abiogenesis. He along with Lister used their observations to develop health measures that would kill harmful bacteria. Koch formed postulates regarding germ theory and tested them by isolating various microorganisms (such as anthrax, tuberculosis, and cholera) that caused diseases.<ref name="SAGEPubMattingly"/> {{wpl|Koch's postulates}} are:

*The microorganism must be found in any organism that has contracted it but not in a healthy organism.
*The microorganism must be removed from the afflicted organism and developed in a pure culture.
*The cultured microorganism should infect healthy organisms when introduced to them. 
*The microorganism must be reisolated from the inoculated, diseased experimental host and marked as the same as the same causative agent originally used.<ref name="SAGEPubMattingly"/>

Though this was massive evidence for germ theory, there are now some obvious limitations. Viruses had not yet been discovered and can not be cultured independently, some things may be ''more'' affected than others (a cow versus a human, for example) or some not at all by a pathogen, and some hosts can't be infected. [[Polymerase chain reaction]] (PCR) testing is one method used today that can be used to diagnose infectious diseases caused by viruses.<ref name="SAGEPubMattingly"/> Some newer writings have expanded on Koch's postulates (see {{wpl|Molecular Koch's postulates}}) to otherwise cover gaps in his observations afforded by more recent discoveries, such as the {{wpl|Bradford Hill criteria}} (though some fusion of Koch and Hill's criteria are the most advisable).<ref name="SAGEPubMattingly"/><ref name="Gorski2021"/>

==Modern era==
Before the onset of the [[AIDS]] epidemic, it was thought that infectious diseases were on their way to being wiped out, penicillin was paraded as a miracle drug (and it certainly was) and a step shy of complete success. Still, today reemerging pathogens such as ''Staphylococcus aureus'' become resistant to old defenses and infect again. Many pathogens mutate, {{wpl|Recombinant_DNA | combine with the DNA}} of other, dead bacteria or sexually transfer ribosomal information between one another. Even unaltered pathogens that have been long-conquered pose an incredible risk to [[Anti-vaccination movement|a population with misconceptions and wariness of vaccines]] (and so avoids them).

Members that choose for themselves or their children to remain unvaccinated can pose a danger or inconvenience to vaccinated members of the population. Costs of treating preventable disease later in life can be monetary, loss of time (and time is money), and should a person who chose to remain unvaccinated die after attempts to treat them (wasting the resources) the population will suffer the loss with emotional grief and resources and money lost with disposing of the body. Vaccination is relatively inexpensive and vastly more responsible if that vaccination has been properly tested for risk.

==Germ theory denialism==

{{main|Germ theory denialism}}

The new, modern area of pathology has continued to grow in success and sophistication, especially with the study of [[genetics]] and [[genomics]] and just plain [[statistics]]. Despite this, a fringe [[Germ theory denialism|denialist movement]] has cropped up in recent years, and many forms of [[alternative medicine]] either ignore or outright deny germ theory. This will likely be to their own undoing and make them responsible for any harm to their children or others.

==Notes==
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==References==
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[[Category:Biology]]
[[Category:Medicine]]
[[Category:Disease]]

Categories: Biology, Medicine, Disease