Editing Plague (disease) (section)

==Cause==
[[File:Xenopsylla chepsis (oriental rat flea).jpg|thumb|The [[Oriental rat flea]] (''Xenopsylla cheopis'') engorged with blood after a blood meal. This species of flea is the primary [[Vector (epidemiology)|vector]] for the transmission of ''Yersinia pestis'', the organism responsible for bubonic plague in most plague [[epidemic]]s in Asia, Africa, and South America. Both male and female fleas [[hematophagy|feed on blood]] and can transmit the infection.]]
[[File:Ulceration of flea bite cause by yersinia pestis.jpg|thumb|A child bitten by a flea [[Infection|infected]] with the bacterium ''Yersinia pestis''. ''Y. pestis'', a member of the family [[Yersiniaceae]], has caused the bite to become [[Ulcer (dermatology)|ulcerated]].]]
Transmission of ''Y. pestis'' to an uninfected individual is possible by any of the following means:<ref name="PM">'' Plague Manual: Epidemiology, Distribution, Surveillance and Control'', pp. 9, 11. WHO/CDS/CSR/EDC/99.2</ref>
* droplet contact&nbsp;– coughing or sneezing on another person
* direct physical contact&nbsp;– touching an infected person, including sexual contact
* indirect contact&nbsp;– usually by touching [[soil contamination]] or a contaminated surface
* airborne transmission&nbsp;– if the microorganism can remain in the air for long periods
* fecal-oral transmission&nbsp;– usually from contaminated food or water sources
* [[vector borne transmission]]&nbsp;– carried by insects or other animals.
''Yersinia pestis'' circulates in animal reservoirs, particularly in rodents, in the natural foci of infection found on all continents except Australia. The natural foci of plague are situated in a broad belt in the tropical and sub-tropical latitudes and the warmer parts of the temperate latitudes around the globe, between the parallels 55° N and 40° S.<ref name=PM/>
Contrary to popular belief, rats did not directly start the spread of the bubonic plague. It is mainly a disease in the [[flea]]s (''[[Xenopsylla cheopis]]'') that infested the rats, making the rats themselves the first victims of the plague. Rodent-borne infection in a human occurs when a person is bitten by a flea that has been infected by biting a rodent that itself has been infected by the bite of a flea carrying the disease. The bacteria multiply inside the flea, sticking together to form a plug that blocks its stomach and causes it to starve. The flea then bites a host and continues to feed, even though it cannot quell its hunger, and consequently, the flea vomits blood tainted with the bacteria back into the bite wound. The bubonic plague bacterium then infects a new person and the flea eventually dies from starvation. Serious outbreaks of plague are usually started by other disease outbreaks in rodents or a rise in the rodent population.<ref>{{Cite journal|last=Yersin|first=Alexandre|year=1894|title=La peste bubonique à Hong-Kong|url=http://www.biusante.parisdescartes.fr/histoire/medica/resultats/index.php?p=3&cote=epo1234&do=page|journal=Annales de l'Institut Pasteur|volume=8|pages=662–67}}</ref>

A 21st-century study of a 1665 outbreak of [[Eyam#1665 plague outbreak|plague in the village of Eyam]] in England's Derbyshire Dales&nbsp;– which isolated itself during the outbreak, facilitating modern study&nbsp;– found that three-quarters of cases are likely to have been due to human-to-human transmission, especially within families, a much larger proportion than previously thought.<ref>{{cite web |url=https://www.bbc.co.uk/news/uk-england-derbyshire-51904810 |title=Coronavirus: What can the 'plague village of Eyam teach us?|website=BBC News |author=Greig Watson |date= 22 April 2020}}</ref>