Editing Black Death (section)

===Causes===

====Early theory====
{{Main|Theories of the Black Death}}

A report by the Medical Faculty of Paris stated that a conjunction of planets had caused "a great pestilence in the air" ([[miasma theory]]).{{sfn|Horrox|1994|p=159}} Muslim religious scholars taught that the pandemic was a "martyrdom and mercy" from God, assuring the believer's place in paradise. For non-believers, it was a punishment.{{sfn|Kelly|2006}}{{Page needed|date=October 2024}} Some Muslim doctors cautioned against trying to prevent or treat a disease sent by God. Others adopted preventive measures and treatments for plague used by Europeans. These Muslim doctors also depended on the writings of the ancient Greeks.<ref>{{cite book | vauthors = al-Asqalani IH |title=Badhl aI-md'On fi fadi at-ld'an |location=Cairo |url=https://archive.org/details/Library.mmn_20150901/mode/2up}}</ref><ref>{{cite thesis |vauthors=Legan JA |title=The medical response to the Black Death |date=2015 |type=B.A. |work=Senior Honors Projects |number=103 |url=https://commons.lib.jmu.edu/honors201019/103 |publisher=James Madison University |access-date=3 December 2020 |archive-date=19 October 2021 |archive-url=https://web.archive.org/web/20211019202939/https://commons.lib.jmu.edu/honors201019/103/ |url-status=live }}</ref>

====Predominant modern theory====
{{Multiple image
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|image1 = Xenopsylla chepsis (oriental rat flea).jpg
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|caption1 = The [[Oriental rat flea]] (''Xenopsylla cheopis'') engorged with blood. This [[species]] of flea is the primary [[vector (epidemiology)|vector]] for the transmission of ''[[Yersinia pestis]]'', the organism responsible for spreading bubonic plague in most plague epidemics. Both male and female fleas [[hematophagy|feed on blood]] and can transmit the infection.
|image2 = Flea infected with yersinia pestis.jpg
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|caption2 = Oriental rat flea (''Xenopsylla cheopis'') infected with the ''[[Yersinia pestis]]'' [[bacteria|bacterium]] which appears as a dark mass in the gut. The foregut (''proventriculus'') of this flea is blocked by a ''Y. pestis'' [[biofilm]]; when the flea feeds on an uninfected [[host (biology)|host]] ''Y. pestis'' is regurgitated into the wound, causing infection.
}}

Due to [[Crisis of the Late Middle Ages#Climate change and plague pandemic correlation|climate change in Asia]], rodents began to flee the dried-out grasslands to more populated areas, spreading the disease.{{sfn|Tignor|Brown|Liu|Shaw|2014|p=407}} The plague disease, caused by the bacterium ''[[Yersinia pestis]]'', is [[enzootic]] (commonly present) in populations of fleas carried by ground [[rodent]]s, including [[marmot]]s, in various areas, including [[Central Asia]], [[Kurdistan]], [[West Asia]], [[North India]], [[Uganda]], and the western United States.{{sfn|Ziegler|1998|p=25}}<ref>{{Cite web|url=https://www.cdc.gov/plague/maps/index.html|title=Maps and Statistics: Plague in the United States|date=25 November 2019|website=[[Centers for Disease Control and Prevention]]|access-date=8 April 2020|archive-date=8 April 2020|archive-url=https://web.archive.org/web/20200408090846/https://www.cdc.gov/plague/maps/index.html|url-status=live}}</ref>

''Y. pestis'' was discovered by [[Alexandre Yersin]], a pupil of [[Louis Pasteur]], during an [[1894 Hong Kong plague|epidemic of bubonic plague]] in Hong Kong in 1894; Yersin also proved this bacterium was present in rodents and suggested the rat was the main vehicle of transmission.{{sfn|Arrizabalaga|2010}}<ref>{{Cite journal| vauthors = Yersin A |year=1894|title=La peste bubonique a Hong-Kong|url=https://gallica.bnf.fr/ark:/12148/bpt6k58345103/f54|journal=Annales de l'Institut Pasteur: Journal de microbiologie|volume=8|issue=9|pages=662–67|issn=0020-2444|via=Gallica|access-date=12 April 2020|archive-date=12 April 2020|archive-url=https://web.archive.org/web/20200412092843/https://gallica.bnf.fr/ark:/12148/bpt6k58345103/f54|url-status=live}}</ref> The mechanism by which ''Y. pestis'' is usually transmitted was established in 1898 by [[Paul-Louis Simond]] and was found to involve the bites of fleas whose [[midgut]]s had become obstructed by replicating ''Y. pestis'' several days after feeding on an infected host.<ref>{{cite journal |last1=Simond |first1=P.-L. |title=La propagation de la peste |journal=Annales de l'Institut Pasteur |date=October 1898 |volume=12 |issue=10 |pages=625–687 |url=https://www.biodiversitylibrary.org/item/22266#page/633/mode/1up |trans-title=The spread of the plague |language=French |access-date=18 July 2024 |archive-date=18 July 2024 |archive-url=https://web.archive.org/web/20240718010607/https://www.biodiversitylibrary.org/item/22266#page/633/mode/1up |url-status=live }}  From p. 674:  ''"Nous avon pratiqué un certain nombre de fois l'examen microscopique du contenu intestinal des puces recueillies sur les rats spontanément pestiférés, et dans plusieurs cas nous avons constaté la présence d'un bacille morphologiquement semblable à celui de la peste."'' ("We carried out a number of times microscopic examinations of the intestinal contents of fleas [which were] collected from rats [which had become] infected with plague, and in several cases we noted the presence of a bacillus [which was] morphologically similar to that of the plague.")</ref> This blockage starves the fleas, drives them to aggressive feeding behaviour, and causes them to try to clear the blockage via [[vomiting|regurgitation]], resulting in thousands of plague bacteria flushing into the feeding site and infecting the host. The bubonic plague mechanism was also dependent on two populations of rodents: one resistant to the disease, which act as [[host (biology)|host]]s, keeping the disease [[endemic (epidemiology)|endemic]], and a second that lacks resistance. When the second population dies, the fleas move on to other hosts, including people, thus creating a human [[epidemic typhus|epidemic]].{{sfn|Christakos|Olea|Serre|Wang|2005|pp=110–14}}

====DNA evidence====
[[File:Bubonic plague victims-mass grave in Martigues, France 1720-1721.jpg|thumb|Skeletons in a mass grave from 1720 to 1721 in [[Martigues]], near [[Marseille]] in southern France, yielded molecular evidence of the ''orientalis'' strain of ''Yersinia pestis'', the organism responsible for bubonic plague. The second pandemic of bubonic plague was active in Europe from&nbsp;1347, the beginning of the Black Death, until 1750.]]

Definitive confirmation of the role of ''Y. pestis'' arrived in 2010 with a publication in ''[[PLOS Pathogens]]'' by Haensch et al.{{sfn|Haensch|Bianucci|Signoli|Rajerison|2010}}{{efn|In 1998, Drancourt et al. reported the detection of ''Y. pestis'' DNA in human dental pulp from a medieval grave.<ref>{{cite journal | vauthors = Drancourt M, Aboudharam G, Signoli M, Dutour O, Raoult D | title = Detection of 400-year-old Yersinia pestis DNA in human dental pulp: an approach to the diagnosis of ancient septicemia | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 95 | issue = 21 | pages = 12637–12640 | date = October 1998 | pmid = 9770538 | pmc = 22883 | doi = 10.1073/pnas.95.21.12637 | bibcode = 1998PNAS...9512637D | doi-access = free  | issn=0027-8424}}</ref> Another team led by [[Marcus Thomas Pius Gilbert|Tom Gilbert]] cast doubt on this identification{{sfn|Gilbert|Cuccui|White|Lynnerup|2004}} and the techniques employed, stating that this method "does not allow us to confirm the identification of Y. pestis as the [[etiology|aetiological]] agent of the Black Death and subsequent plagues. In addition, the utility of the published tooth-based ancient DNA technique used to diagnose fatal [[bacteremia|bacteraemia]]s in historical epidemics still awaits independent corroboration".}} They assessed the presence of [[DNA]]/[[RNA]] with [[polymerase chain reaction]] (PCR) techniques for ''Y. pestis'' from the [[dental alveolus|tooth socket]]s in human skeletons from mass graves in northern, central and southern Europe that were associated archaeologically with the Black Death and subsequent resurgences. The authors concluded that this new research, together with prior analyses from the south of France and Germany, "ends the debate about the cause of the Black Death, and unambiguously demonstrates that ''Y. pestis'' was the [[disease causative agent|causative agent]] of the epidemic plague that devastated Europe during the Middle Ages".{{sfn|Haensch|Bianucci|Signoli|Rajerison|2010}} In 2011 these results were further confirmed with genetic evidence derived from Black Death victims in the [[East Smithfield]] burial site in England. Schuenemann et al. concluded in 2011 "that the Black Death in medieval Europe was caused by a variant of ''Y. pestis'' that may no longer exist".{{sfn|Bos|2011}}

Later in 2011, [[Kirsten Bos|Bos]] et al. reported in ''[[Nature (journal)|Nature]]'' the first draft genome of ''Y. pestis'' from plague victims from the same East Smithfield cemetery and indicated that the strain that caused the Black Death is ancestral to most modern strains of ''Y. pestis''.{{sfn|Bos|2011}}

Later genomic papers have further confirmed the [[phylogenetics|phylogenetic]] placement of the ''Y. pestis'' strain responsible for the Black Death as both the ancestor{{sfn|Spyrou|Keller|Tukhbatova|Scheib|2019}} of later plague epidemics—including the [[third plague pandemic]]—and the descendant{{sfn|Wagner|Klunk|Harbeck|Devault|2014}} of the strain responsible for the [[Plague of Justinian]]. In addition, plague genomes from prehistory have been recovered.{{sfn|Rasmussen|Allentoft|Nielsen|Orlando|2015}}

DNA taken from 25 skeletons from 14th-century London showed that plague is a strain of ''Y. pestis'' almost identical to that which [[21st-century Madagascar plague outbreaks|hit Madagascar in 2013]].<ref name=guardian/><ref>{{Cite news|url=https://www.bbc.co.uk/news/science-environment-26770334|title=Black Death skeletons unearthed by Crossrail project| vauthors = Morgan J |date=30 March 2014|work=BBC News|access-date=20 August 2017|language=en-GB|archive-url=https://web.archive.org/web/20171225001808/http://www.bbc.co.uk/news/science-environment-26770334|archive-date=25 December 2017|url-status=live}}</ref> Further DNA evidence also proves the role of ''Y. pestis'' and traces the source to the [[Tian Shan]] mountains in [[Kyrgyzstan]].<ref>{{cite web|url=https://www.cnn.com/2022/06/15/health/black-death-plague-source-identified-scn/index.html|publisher=CNN|last=Hunt|first=Katie|title=DNA analysis reveals source of Black Death|date=June 15, 2022|access-date=June 18, 2022|archive-date=18 June 2022|archive-url=https://web.archive.org/web/20220618150441/https://www.cnn.com/2022/06/15/health/black-death-plague-source-identified-scn/index.html|url-status=live}}</ref>

====Alternative explanations====
Researchers are hampered by a lack of reliable statistics from this period. Most work has been done on the spread of the disease in England, where estimates of overall population at the start of the plague vary by over 100%, as no census was undertaken in England between the time of publication of the [[Domesday Book]] of 1086 and the [[poll tax#Great Britain|poll tax]] of the year 1377.{{sfn|Ziegler|1998|p=233}} Estimates of plague victims are usually [[extrapolation|extrapolate]]d from figures for the clergy.

[[Mathematical modelling]] is used to match the spreading patterns and the means of [[transmission (medicine)|transmission]]. In 2018 researchers suggested an alternative model in which ''"the disease was spread from human fleas and body lice to other people".'' The second model claims to better fit the trends of the plague's death toll, as the rat-flea-human hypothesis would have produced a delayed but very high spike in deaths, contradicting historical death data.<ref>{{cite news| vauthors = Guarino B |date=2018-01-16|newspaper=[[The Washington Post]]|url=https://www.washingtonpost.com/news/speaking-of-science/wp/2018/01/16/the-classic-explanation-for-the-black-death-plague-is-wrong-scientists-say/|title=The classic explanation for the Black Death plague is wrong, scientists say|archive-url=https://archive.today/20180122005044/https://www.washingtonpost.com/news/speaking-of-science/wp/2018/01/16/the-classic-explanation-for-the-black-death-plague-is-wrong-scientists-say/|archive-date=22 January 2018|access-date=2 April 2020|url-status=live}}</ref><ref>{{cite news|title=Rats May Not Be to Blame for Spreading the 'Black Death'| vauthors = Rettner R |publisher=[[Live Science]]|date=2018-01-17|url=https://www.livescience.com/61444-black-death-cause-found-transmission.html|access-date=2 April 2020|archive-date=28 March 2020|archive-url=https://web.archive.org/web/20200328004408/https://www.livescience.com/61444-black-death-cause-found-transmission.html|url-status=live}}</ref> The Oriental rat flea has poor survival in cooler climates and reevaluation suggests the [[humean flea]] was the principal vector of plague epidemics in Northern Europe.<ref name="durden">{{cite book | last=Durden | first=Lance A. | last2=Hinkle | first2=Nancy C. | title=Medical and Veterinary Entomology | chapter=Fleas (Siphonaptera) | publisher=Elsevier | date=2019 | isbn=978-0-12-814043-7 | doi=10.1016/b978-0-12-814043-7.00010-8 | page=145–169}}</ref>

[[Lars Walløe]] argued that these authors "take it for granted that Simond's infection model, black rat → rat flea → human, which was developed to explain the spread of plague in India, is the only way an epidemic of ''Yersinia pestis'' infection could spread".{{sfn|Walløe|2008|p=69}} Similarly, [[Monica Green (historian)|Monica Green]] has argued that greater attention is needed to the range of (especially non-[[commensalism|commensal]]) animals that might be involved in the transmission of plague.{{sfn|Green|2015|pages=31ff}}

Archaeologist Barney Sloane has argued that there is insufficient evidence of the extinction of numerous rats in the archaeological record of the medieval waterfront in London, and that the disease spread too quickly to support the thesis that ''Y. pestis'' was spread from fleas on rats; he argues that transmission must have been person to person.<ref>{{Cite news | vauthors = Kennedy M |title=Black Death study lets rats off the hook |journal=The Guardian |isbn=978-0-7524-2829-1 |place=London |url=https://www.theguardian.com/world/2011/aug/17/black-death-rats-off-hook |year=2011 |access-date=14 December 2016 |archive-url=https://web.archive.org/web/20130827191239/http://www.theguardian.com/world/2011/aug/17/black-death-rats-off-hook |archive-date=27 August 2013 |url-status=live }}</ref>{{sfn|Sloane|2011}} This theory is supported by research in 2018 which suggested transmission was more likely by body lice and [[Oriental rat flea|flea]]s during the [[second plague pandemic]].{{sfn|Dean|Krauer|Walløe|Lingjærde|2018}}

====Summary====
Academic debate continues, but no single alternative explanation for the plague's spread has achieved widespread acceptance.{{sfn|Christakos|Olea|Serre|Wang|2005|pp=110–14}} Many scholars arguing for ''Y. pestis'' as the major agent of the pandemic suggest that its extent and symptoms can be explained by a combination of bubonic plague with other diseases, including [[typhus]], [[smallpox]], and [[respiratory tract infection|respiratory infection]]s. In addition to the bubonic infection, others point to additional [[Sepsis|septicemic]] and [[Pneumonia|pneumonic]] forms of plague, which lengthen the duration of outbreaks throughout the seasons and help account for its high mortality rate and additional recorded symptoms.<ref name="Byrne2004pp21-9">{{harvnb|Byrne|2004|pp=21–29}}</ref> In 2014, [[Public Health England]] announced the results of an examination of 25 bodies exhumed in the [[Clerkenwell]] area of London, as well as of wills registered in London during the period, which supported the pneumonic hypothesis.<ref name="guardian" /> Currently, while [[osteoarchaeology|osteoarcheologist]]s have conclusively verified the presence of ''Y. pestis'' bacteria in burial sites across northern Europe through examination of bones and [[dental pulp]], no other epidemic pathogen has been discovered to bolster the alternative explanations.{{sfn|Snowden|2019|pp=50–51}}