Editing Yellow fever (section)

==Epidemiology==
Yellow fever is [[Endemic (epidemiology)|common]] in tropical and subtropical areas of South America and Africa.<ref>{{cite book | vauthors = Simon LV, Hashmi MF, Torp KD | chapter = Yellow Fever |date=2022 |chapter-url=http://www.ncbi.nlm.nih.gov/books/NBK470425/ | title = StatPearls |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=29262028 |access-date=2022-04-25 }}</ref> Worldwide, about 600 million people live in endemic areas. The WHO estimates 200,000 cases of yellow fever worldwide each year.<ref>{{Cite web |date=2019-02-19 |title=Global Health - Newsroom - Yellow Fever |url=https://www.cdc.gov/globalhealth/newsroom/topics/yellowfever/index.html |access-date=2022-04-25 |website=www.cdc.gov |language=en-us}}</ref> About 15% of people infected with yellow fever progress to a severe form of the illness, and up to half of those will die, as there is no cure for yellow fever.<ref>{{Cite web|title=Yellow fever vaccination booster not needed|url=https://www.who.int/news/item/17-05-2013-yellow-fever-vaccination-booster-not-needed|access-date=2021-10-09|website=World Health Organization|language=en}}</ref>

===Africa===
[[File:Yellow fever Africa 2009.jpeg|thumb|upright=1.2|Areas with risk of yellow fever in Africa (2017)]]

An estimated 90% of yellow fever infections occur on the African continent.<ref name=Toll2009/> In 2016, [[2016 Angola and DR Congo yellow fever outbreak|a large outbreak originated in Angola]] and spread to neighboring countries before being contained by a massive vaccination campaign.<ref>{{Cite web |title=Mass vaccination campaign to protect millions against yellow fever in Angola and the Democratic Republic of the Congo |url=https://www.who.int/news-room/feature-stories/detail/mass-vaccination-campaign-to-protect-millions-against-yellow-fever-in-angola-and-democratic-republic-of-the-congo |access-date=2022-04-25 |website=World Health Organization |language=en}}</ref> In March and April 2016, 11 imported cases of the Angola genotype in unvaccinated Chinese nationals were reported in China, the first appearance of the disease in Asia in recorded history.<ref>{{cite web |title=Yellow Fever – China |url=https://www.who.int/csr/don/22-april-2016-yellow-fever-china/en/ |website=World Health Organization |access-date=9 February 2017 |archive-url=https://web.archive.org/web/20170319162041/http://who.int/csr/don/22-april-2016-yellow-fever-china/en/ |archive-date=19 March 2017}}</ref><ref>{{cite journal | vauthors = Woodall JP, Yuill TM | title = Why is the yellow fever outbreak in Angola a 'threat to the entire world'? | journal = International Journal of Infectious Diseases | volume = 48 | pages = 96–97 | date = July 2016 | pmid = 27163382 | doi = 10.1016/j.ijid.2016.05.001 | doi-access = free }}</ref>

[[Phylogenetic]] analysis has identified seven [[genotype]]s of yellow fever viruses, and they are assumed to be differently adapted to humans and to the vector ''A. aegypti''. Five genotypes (Angola, Central/East Africa, East Africa, West Africa I, and West Africa II) occur only in Africa. West Africa genotype I is found in [[Nigeria]] and the surrounding region.<ref name=Mutebi2002>{{cite journal | vauthors = Mutebi JP, Barrett AD | title = The epidemiology of yellow fever in Africa | journal = Microbes and Infection | volume = 4 | issue = 14 | pages = 1459–1468 | date = November 2002 | pmid = 12475636 | doi = 10.1016/S1286-4579(02)00028-X }}</ref> West Africa genotype I appears to be especially infectious, as it is often associated with major outbreaks. The three genotypes found outside of Nigeria and Angola occur in areas where outbreaks are rare. Two outbreaks, in Kenya (1992–1993) and Sudan (2003 and 2005), involved the East African genotype, which had remained undetected in the previous 40 years.<ref name=Ellis2008>{{cite journal | vauthors = Ellis BR, Barrett AD | title = The enigma of yellow fever in East Africa | journal = Reviews in Medical Virology | volume = 18 | issue = 5 | pages = 331–346 | year = 2008 | pmid = 18615782 | doi = 10.1002/rmv.584 }}</ref>

===South America===
[[File:Yellow fever South America 2009.jpeg|thumb|upright=1.2|Areas with risk of yellow fever in South America (2018)]]

In South America, two genotypes have been identified (South American genotypes I and II).<ref name=Barr2007/> Based on phylogenetic analysis these two genotypes appear to have originated in West Africa<ref name="Mutebi2004">{{cite journal | vauthors = Mutebi JP, Rijnbrand RC, Wang H, Ryman KD, Wang E, Fulop LD, Titball R, Barrett AD | display-authors = 6 | title = Genetic relationships and evolution of genotypes of yellow fever virus and other members of the yellow fever virus group within the Flavivirus genus based on the 3' noncoding region | journal = Journal of Virology | volume = 78 | issue = 18 | pages = 9652–9665 | date = September 2004 | pmid = 15331698 | pmc = 515011 | doi = 10.1128/JVI.78.18.9652-9665.2004 }}</ref> and were first introduced into Brazil.<ref name="Auguste2010">{{cite journal | vauthors = Auguste AJ, Lemey P, Pybus OG, Suchard MA, Salas RA, Adesiyun AA, Barrett AD, Tesh RB, Weaver SC, Carrington CV | display-authors = 6 | title = Yellow fever virus maintenance in Trinidad and its dispersal throughout the Americas | journal = Journal of Virology | volume = 84 | issue = 19 | pages = 9967–9977 | date = October 2010 | pmid = 20631128 | pmc = 2937779 | doi = 10.1128/JVI.00588-10 }}</ref> The date of introduction of the predecessor African genotype which gave rise to the South American genotypes appears to be 1822 (95% confidence interval 1701 to 1911).<ref name="Auguste2010"/> The historical record shows an outbreak of yellow fever occurred in Recife, Brazil, between 1685 and 1690. The disease seems to have disappeared, with the next outbreak occurring in 1849.<ref>{{Cite book | vauthors = Bhattacharya A |url=https://books.google.com/books?id=b6ynBQAAQBAJ&pg=PA92 |title=A REVIEW ON VIRAL HEMORRHAGIC FEVER | date=7 June 2013 |publisher=Lulu.com |isbn=978-1-304-11397-9 |language=en}}</ref> It was likely introduced with the trafficking of slaves through the [[Atlantic slave trade|slave trade]] from Africa. Genotype I has been divided into five subclades, A through E.<ref name=deSouza2010>{{cite journal | vauthors = de Souza RP, Foster PG, Sallum MA, Coimbra TL, Maeda AY, Silveira VR, Moreno ES, da Silva FG, Rocco IM, Ferreira IB, Suzuki A, Oshiro FM, Petrella SM, Pereira LE, Katz G, Tengan CH, Siciliano MM, Dos Santos CL | display-authors = 6 | title = Detection of a new yellow fever virus lineage within the South American genotype I in Brazil | journal = Journal of Medical Virology | volume = 82 | issue = 1 | pages = 175–185 | date = January 2010 | pmid = 19950229 | doi = 10.1002/jmv.21606 }}</ref>

In late 2016, a large outbreak began in [[Minas Gerais]] state of Brazil that was characterized as a sylvatic or jungle [[epizootic]].<ref name="Faria2017">{{cite web |vauthors = Faria NR | title = Real-time Genomic Surveillance of the Yellow Fever Virus Outbreak in Brazil, 2017 |website=Virological | date = May 2017 |url=https://virological.org/t/real-time-genomic-surveillance-of-the-yellow-fever-virus-outbreak-in-brazil-2017/182}}</ref>  Real-time phylogenetic investigations at the epicentre of the outbreak revealed that the outbreak was caused by the introduction of a virus lineage from the Amazon region into the southeast region around July 2016,<ref name="Faria2018">{{cite journal |vauthors = Faria NR, Kraemer MU, Hill SH, Goes de Jesus J, Aguiar RS, Iani FC, etal | title = Genomic and epidemiological monitoring of yellow fever virus transmission potential | journal = Science | volume = 361 | issue = 6405 | pages = 894–899 | date = August 2018 | pmid = 30139911 | pmc = 6874500 | doi =  10.1126/science.aat7115| bibcode = 2018Sci...361..894F }}</ref> spreading rapidly across several neotropical monkey species, including [[brown howler]] monkeys,<ref>{{cite web |title=Yellow fever killing thousands of monkeys in Brazil |url=https://www.sciencedaily.com/releases/2017/03/170322155611.htm |website=www.sciencedaily.com |access-date=24 March 2017 |url-status=live |archive-url=https://web.archive.org/web/20170324174443/https://www.sciencedaily.com/releases/2017/03/170322155611.htm |archive-date=24 March 2017}}</ref> which serve as a [[sentinel species]] for yellow fever. No cases had been transmitted between humans by the ''A. aegypti'' mosquito, which can sustain urban outbreaks that can spread rapidly. In April 2017, the sylvatic outbreak continued moving toward the Brazilian coast, where most people were unvaccinated.<ref name="Yellow fever – Brazil"/> By the end of May the outbreak appeared to be declining after more than 3,000 suspected cases, 758 confirmed and 264 deaths confirmed to be yellow fever.<ref>{{cite web |title=ProMED-mail post Yellow fever - Americas (47): Brazil, PAHO/WHO |url=http://www.promedmail.org/post/5071826 |website=www.promedmail.org |publisher=International Society for Infectious Diseases |access-date=1 June 2017 |language=en |url-status=live |archive-url=https://web.archive.org/web/20170908222719/http://www.promedmail.org/post/5071826 |archive-date=8 September 2017}}</ref> The Health Ministry launched a vaccination campaign and was concerned about spread during the [[Carnival]] season in February and March. The CDC issued a [[Centers for Disease Control and Prevention#Travelers' Health|Level 2 alert (practice enhanced precautions.)]]<ref>{{cite web |title=Yellow Fever in Brazil – Alert – Level 2, Practice Enhanced Precautions – Travel Health Notices {{!}} Travelers' Health {{!}} CDC |url=https://wwwnc.cdc.gov/travel/notices/alert/yellow-fever-brazil |website=wwwnc.cdc.gov |access-date=1 June 2017 |language=en-us |url-status=live |archive-url=https://web.archive.org/web/20170525133831/https://wwwnc.cdc.gov/travel/notices/alert/yellow-fever-brazil |archive-date=25 May 2017}}</ref>

A Bayesian analysis of genotypes I and II has shown that genotype I accounts for virtually all the current infections in [[Brazil]], [[Colombia]], [[Venezuela]], and [[Trinidad]] and [[Tobago]], while genotype II accounted for all cases in [[Peru]].<ref name="Mir2017">{{cite journal | vauthors = Mir D, Delatorre E, Bonaldo M, Lourenço-de-Oliveira R, Vicente AC, Bello G | title = Phylodynamics of Yellow Fever Virus in the Americas: new insights into the origin of the 2017 Brazilian outbreak | journal = Scientific Reports | volume = 7 | issue = 1 | page = 7385 | date = August 2017 | pmid = 28785067 | pmc = 5547128 | doi = 10.1038/s41598-017-07873-7 | bibcode = 2017NatSR...7.7385M }}</ref> Genotype I originated in the northern Brazilian region around 1908 (95% highest posterior density interval [HPD]: 1870–1936). Genotype II originated in Peru in 1920 (95% HPD: 1867–1958).<ref name="Mir2017"/> The estimated rate of mutation for both genotypes was about 5 × 10<sup>−4</sup> substitutions/site/year, similar to that of other RNA viruses.{{citation needed|date=November 2024}}

===Asia===
The main vector (''A. aegypti'') also occurs in tropical and subtropical regions of Asia, the Pacific, and Australia, but yellow fever had never occurred there until jet travel introduced 11 cases from the [[2016 Angola and DR Congo yellow fever outbreak]] in Africa. Proposed explanations include:<ref>{{cite journal | vauthors = Lataillade LG, Vazeille M, Obadia T, Madec Y, Mousson L, Kamgang B, Chen CH, Failloux AB, Yen PS | display-authors = 6 | title = Risk of yellow fever virus transmission in the Asia-Pacific region | journal = Nature Communications | volume = 11 | issue = 1 | page = 5801 | date = November 2020 | pmid = 33199712 | pmc = 7669885 | doi = 10.1038/s41467-020-19625-9 | bibcode = 2020NatCo..11.5801L }}</ref>
* That the strains of the mosquito in the east are less able to transmit Yellow fever virus.{{citation needed|date=November 2024}}
* That immunity is present in the populations because of other diseases caused by related viruses (for example, [[dengue]]).<ref>{{Cite web |title=Dengue and severe dengue |url=https://www.who.int/news-room/fact-sheets/detail/dengue-and-severe-dengue |access-date=2022-04-25 |website=World Health Organization |language=en}}</ref>
* That the disease was never introduced because the shipping trade was insufficient.

But none is considered satisfactory.<ref>{{cite book | veditors = Vainio J, Cutts F |title=Yellow Fever |publisher=WHO Division of Emerging and other Communicable Diseases Surveillance and Control |year=1998  }}</ref><ref>{{cite journal | vauthors = Monath TP |title= The absence of yellow fever in Asia: hypotheses. A cause for concern? |journal= Virus Inf Exch Newslett |pages=106–7 |date= 1989 }}</ref> Another proposal is the absence of a slave trade to Asia on the scale of that to the Americas.<ref name="Cathey2014">{{cite journal | vauthors = Cathey JT, Marr JS | title = Yellow fever, Asia and the East African slave trade | journal = Transactions of the Royal Society of Tropical Medicine and Hygiene | volume = 108 | issue = 5 | pages = 252–257 | date = May 2014 | pmid = 24743951 | doi = 10.1093/trstmh/tru043 }}</ref> The [[trans-Atlantic slave trade]] probably introduced yellow fever into the Western Hemisphere from Africa.<ref name="Bryant2007">{{cite journal | vauthors = Bryant JE, Holmes EC, Barrett AD | title = Out of Africa: a molecular perspective on the introduction of yellow fever virus into the Americas | journal = PLOS Pathogens | volume = 3 | issue = 5 | pages = e75 | date = May 2007 | pmid = 17511518 | pmc = 1868956 | doi = 10.1371/journal.ppat.0030075 | doi-access = free }}</ref>