Editing Lassa fever (section)

==Epidemiology==
[[file:Lassa fever Outbreak Distribution Map.svg|thumb|350px|Lassa fever distribution. Countries reporting continued spread of disease and outbreaks in blue. Countries reporting a few cases, periodic isolation of virus, or serological evidence of infection in green. Countries with unknown status in grey.<ref>{{Cite web|url=https://www.cdc.gov/vhf/lassa/outbreaks/index.html|title=Outbreak Distribution Map of Lassa Fever|publisher=CDC|date=2019-03-04|website=www.cdc.gov|language=en-us|access-date=2019-04-27}}</ref>]]

There are about 300,000 to 500,000 cases which result in 5,000 deaths a year.<ref name=Ogbu_2007/><ref name=BMJ2017/> One estimate places <ref>{{Cite web |title=Lassa Fever |url=https://africacdc.org/disease/lassa-fever/ |access-date=2022-04-23 |website=Africa CDC |language=en-GB |archive-date=29 June 2022 |archive-url=https://web.archive.org/web/20220629132022/https://africacdc.org/disease/lassa-fever/ |url-status=live }}</ref> the number as high as 3 million cases per year.<ref name=Go2012/>

Estimates of Lassa fever are complicated by the lack of easy-available diagnosis, limited public health surveillance infrastructure, and high clustering of incidence near high intensity sampling.<ref name=":1" />

The infection affects females 1.2 times more than males. The age group predominantly infected is 21–30 years.<ref>{{Cite web|url=https://www.premiumtimesng.com/news/headlines/381433-lassa-fever-nigerias-death-toll-reaches-144.html|title=Lassa Fever: Nigeria's death toll reaches 144|last=Owoseye|first=Ayodamola|date=2020-03-11|language=en-GB|access-date=2020-03-13|archive-date=12 March 2020|archive-url=https://web.archive.org/web/20200312154450/https://www.premiumtimesng.com/news/headlines/381433-lassa-fever-nigerias-death-toll-reaches-144.html|url-status=live}}</ref>

===Geography===
Lassa high risk areas are near the western and eastern extremes of West Africa. As of 2018, the Lassa belt includes Guinea, Nigeria, Sierra Leone and Liberia.<ref name=JAMA2018>{{cite journal|author1=David Greenky|author2=Barbara Knust|author3=Eric J. Dziuban|title=What Pediatricians Should Know About Lassa Virus|journal=[[JAMA Pediatrics]]|year=2018|volume=172|issue=5|pages=407–408|doi=10.1001/jamapediatrics.2017.5223|pmid=29507948|pmc=5970952}}</ref> As of 2003, 10-16% of people in Sierra Leone and Liberia admitted to hospital had the virus.<ref name="Rich2003" /> The case fatality rate for those who are hospitalized for the disease is about 15-20%. Research showed a twofold increase risk of infection for those living in close proximity to someone with infection symptoms within the last year.<ref>{{Cite web |title=Lassa fever |url=https://www.who.int/news-room/fact-sheets/detail/lassa-fever#:~:text=The%20overall%20case%20fatality%20rate,treatment%20improves%20chances%20of%20survival. |access-date=2025-03-09 |website=www.who.int |language=en}}</ref>

The high risk areas cannot be well defined by any known biogeographical or environmental breaks except for the multimammate rat, particularly Guinea ([[Kindia Region|Kindia]], [[Faranah Region|Faranah]] and [[Nzérékoré Region|Nzérékoré]] regions), Liberia (mostly in [[Lofa County|Lofa]], [[Bong County|Bong]], and [[Nimba County|Nimba]] counties), Nigeria (in about 10 of 36 states) and Sierra Leone (typically from [[Kenema District|Kenema]] and [[Kailahun District|Kailahun]] districts).  It is less common in the Central African Republic, Mali, Senegal and other nearby countries, and less common yet in Ghana and the Democratic Republic of the Congo. Benin had its first confirmed cases in 2014, and Togo had its first confirmed cases in 2016.<ref name="PHE" />

As of 2013, the spread of Lassa outside of West Africa had been very limited. Twenty to thirty cases had been described in Europe, as being caused by importation through infected individuals.<ref name=Go2012/> These cases found outside of West Africa were found to have a high fatality risk because of the delay of diagnosis and treatment due to being unaware of the risk associated with the symptoms.<ref name=Go2012/> Imported cases have not manifested in larger epidemics outside of Africa due to a lack of human to human transmission in hospital settings. An exception had occurred in 2003 when a healthcare worker became infected before the person showed clear symptoms.<ref name=Go2012/>

In October 2024, a resident of [[Iowa]], United States has passed away due to Lassa fever following a trip to West Africa, as reported by the Iowa Department of Health and Human Services.<ref name="Branswell">{{Cite web |last=Branswell |first=Helen |date=2024-10-28 |title=U.S. death from Lassa fever, an Ebola-like virus, is reported in Iowa |url=https://www.statnews.com/2024/10/28/lassa-fever-us-case-iowa-death/ |access-date=2024-10-29 |website=STAT |language=en-US}}</ref> Health officials indicate the person likely contracted Lassa fever—transmissible through contact with infected body fluids or, potentially, with rodents while abroad, according to guidance from the [[Centers for Disease Control and Prevention]].<ref>{{Cite web |last=CDC |date=2024-10-28 |title=Lassa Fever Suspected in Death of U.S. Traveler Returning from West Africa |url=https://www.cdc.gov/media/releases/2024/s1028-lassa-fever.html |access-date=2024-10-29 |website=CDC Newsroom |language=en-us}}</ref>

=== Nigeria ===

====2018 outbreak====
{|class="wikitable" style="float: right; margin:0 1em 0.5em 1em;"
|+ Infections and deaths by country
|-
| '''Country''' || '''Infections''' || '''Deaths'''
|-
| [[Nigeria]] || 2,121 || 132
|-
| [[Liberia]] || 108 || 
|-
| [[Sierra Leone]] || 129 || 12
|-
| [[Guinea]] || 98 || 
|}
An outbreak of Lassa fever occurred in Nigeria during 2018 and spread to 18 of the country's states; it was the largest outbreak of Lassa recorded.<ref>{{cite journal|last1=Maxmen|first1=Amy|title=Deadly Lassa-fever outbreak tests Nigeria's revamped health agency|journal=Nature|volume=555|issue=7697|pages=421–422|date=15 March 2018|doi=10.1038/d41586-018-03171-y|pmid=29565399|language=EN|bibcode=2018Natur.555..421M|doi-access=free}}</ref><ref name=WHO2018-03>{{cite news|title=On the frontlines of the fight against Lassa fever in Nigeria|url=https://www.who.int/features/2018/lassa-fever-nigeria/en/|archive-url=https://web.archive.org/web/20180318094709/http://www.who.int/features/2018/lassa-fever-nigeria/en/|url-status=dead|archive-date=18 March 2018|work=World Health Organization|date=March 2018}}</ref><ref>{{cite news|last1=Beaubien|first1=Jason|title=Nigeria Faces Mystifying Spike in Deadly Lassa Fever|url=https://www.npr.org/sections/goatsandsoda/2018/03/19/587603462/nigeria-faces-mystiifying-spike-in-deadly-lassa-fever|work=NPR|date=19 March 2018|language=en|access-date=18 June 2019|archive-date=19 March 2018|archive-url=https://web.archive.org/web/20180319235226/https://www.npr.org/sections/goatsandsoda/2018/03/19/587603462/nigeria-faces-mystiifying-spike-in-deadly-lassa-fever|url-status=live}}</ref> The outbreak primarily affected [[Nigeria]], [[Liberia]], [[Sierra Leone]], and [[Guinea]], with cases reported since January 2018.<ref>{{Cite journal |last1=Balogun |first1=Oluwafemi O. |last2=Akande |first2=Oluwatosin W. |last3=Hamer |first3=Davidson H. |date=2020-11-23 |title=Lassa Fever: An Evolving Emergency in West Africa |journal=The American Journal of Tropical Medicine and Hygiene |volume=104 |issue=2 |pages=466–473 |doi=10.4269/ajtmh.20-0487 |issn=1476-1645 |pmc=7866331 |pmid=33236712}}</ref><ref>{{Cite web |title=Lassa Fever – Nigeria |url=https://www.who.int/emergencies/disease-outbreak-news/item/01-march-2018-lassa-fever-nigeria-en |access-date=2025-03-21 |website=www.who.int |language=en}}</ref>

As of 25 February 2018, there were 1081 suspected cases and 90 reported deaths; 317 of the cases and 72 deaths were confirmed as Lassa which increased to a total of 431 reported cases in 2018.<ref>{{cite news|url=https://www.who.int/csr/don/01-march-2018-lassa-fever-nigeria/en/|archive-url=https://web.archive.org/web/20180301141952/http://www.who.int/csr/don/01-march-2018-lassa-fever-nigeria/en/|url-status=dead|archive-date=1 March 2018|title=Lassa Fever – Nigeria|date=1 March 2018|work=World Health Organization}}</ref> During the outbreak, a total of 3,498 [[Infection|infections]] were recorded, resulting in 171 deaths. Nigeria was the most severely impacted, accounting for over half of the total cases and fatalities. [[World Health Organization|The World Health Organization]] (WHO) reported on 27 March 2018 that 1,081 suspected cases and 90 deaths had occurred.<ref>{{Cite web |date=2025-03-20 |title=Lassa Fever {{!}} WHO {{!}} Regional Office for Africa |url=https://www.afro.who.int/health-topics/lassa-fever |access-date=2025-03-21 |website=www.afro.who.int |language=en}}</ref> It was one of the most severe Lassa fever outbreaks in the region in recent years, exhausting a significant portion of the global emergency medical response resources.<ref>{{Cite web |last=CDC |date=2025-01-31 |title=About Lassa Fever |url=https://www.cdc.gov/lassa-fever/about/index.html |access-date=2025-03-21 |website=Lassa Fever |language=en-us}}</ref>

Health organizations, including [[Médecins Sans Frontières|Doctors Without Borders]] and the WHO, collaborated with national governments to contain the outbreak through mass awareness campaigns, improved surveillance, and emergency medical interventions. In total, 2.1 million people received preventive health education, while emergency treatment centers were established across affected regions.<ref>{{Cite web |title=Meeting of the Lassa Fever Coalition Governing Entity (LGE) {{!}} West African Health Organization |url=https://www.wahooas.org/web-ooas/en/actualites/meeting-lassa-fever-coalition-governing-entity-lge |access-date=2025-03-21 |website=www.wahooas.org}}</ref><ref>{{Cite journal |last1=Aloke |first1=Chinyere |last2=Obasi |first2=Nwogo Ajuka |last3=Aja |first3=Patrick Maduabuchi |last4=Emelike |first4=Chinedum Uche |last5=Egwu |first5=Chinedu Ogbonnia |last6=Jeje |first6=Olamide |last7=Edeogu |first7=Chuks Oswald |last8=Onisuru |first8=Olalekan Olugbenga |last9=Orji |first9=Obasi Uche |last10=Achilonu |first10=Ikechukwu |date=2023-01-03 |title=Combating Lassa Fever in West African Sub-Region: Progress, Challenges, and Future Perspectives |journal=Viruses |volume=15 |issue=1 |pages=146 |doi=10.3390/v15010146 |doi-access=free |issn=1999-4915 |pmc=9864412 |pmid=36680186}}</ref>

Nigeria was the hardest hit country, with 2,121 cases and 132 deaths reported. The outbreak affected 18 of its 36 [[States of Nigeria|states]], with the highest cases recorded in [[Edo]]''',''' [[Ondo State|Ondo]]''',''' and [[Ebonyi State|Ebonyi States]]. The [[Federal Ministry of Health and Social Welfare|Nigerian Ministry of Health]] launched an extensive awareness campaign and deployed medical teams to affected areas. Emergency supplies, including [[ribavirin]] (an antiviral drug), were distributed, and treatment centers were set up in federal hospitals to manage severe cases.<ref>{{Cite web |title=Nigeria: spread of Lassa fever, by status 2023 {{!}} Statista |url=https://www.statista.com/statistics/1126777/number-of-lassa-fever-cases-in-nigeria/#:~:text=From%20January%20to%20October%202023,in%20several%20West%20African%20countries. |archive-url=http://web.archive.org/web/20240807221000/https://www.statista.com/statistics/1126777/number-of-lassa-fever-cases-in-nigeria/ |archive-date=2024-08-07 |access-date=2025-03-21 |website=Statista |language=en}}</ref><ref>{{Cite web |title=Lassa Fever - Nigeria |url=https://www.who.int/emergencies/disease-outbreak-news/item/lassa-fever---nigeria |access-date=2025-03-21 |website=www.who.int |language=en}}</ref>

==== 2019 outbreak ====
{{Infobox News event
| image = [[File:2009 Africa epidemic.png]]
| caption = Countries affected by the epidemic
| map_size = 50
| place = [[Sierra Leone]], [[Liberia]], [[Guinea]], and [[Nigeria]]
| casualties1 = 1,100 dead
| casualties2 = 25,000 suspected cases
| casualties3 = 
| notes = 
}}
The total cases in Nigeria in 2019 was 810 with 167 deaths, the largest case fatality rate (23.3%) until then.<ref>{{Cite web|url=https://qz.com/africa/1814567/coronavirus-less-deadly-than-nigeria-lassa-fever-viral-outbreak/|title=Nigeria is already dealing with a deadlier viral outbreak than the coronavirus epidemic|last=Edward-Ekpu|first=Uwagbale|website=Quartz Africa|date=8 March 2020|language=en|access-date=2020-03-13|archive-date=13 March 2020|archive-url=https://web.archive.org/web/20200313035110/https://qz.com/africa/1814567/coronavirus-less-deadly-than-nigeria-lassa-fever-viral-outbreak/|url-status=live}}</ref><ref name=":2" />

==== 2020 outbreak ====
The epidemic started from the second week of the January. By the tenth week the total number of cases has risen to 855 and deaths to 144, the case fatality rate of 16.8%.<ref name=":2">{{Cite web|url=https://www.ncdc.gov.ng/themes/common/files/sitreps/f9c5b3d7327f20c15c3916ff5514fb14.pdf|title=Lassa fever situation report|website=Nigeria Centre for Disease Control|date=March 2020|access-date=13 March 2020|archive-date=9 April 2020|archive-url=https://web.archive.org/web/20200409140325/https://www.ncdc.gov.ng/themes/common/files/sitreps/f9c5b3d7327f20c15c3916ff5514fb14.pdf|url-status=dead}}</ref>

====2021 outbreak====
On the 8th of December 2021, the Nigeria Centre for Disease Control (NCDC) was notified of the death of two persons from Lassa fever.<ref>{{Cite web |title=Nigeria Centre for Disease Control |url=https://ncdc.gov.ng/news/349/ncdc-intensifies-activities-for-lassa-fever-surveillance-and-response-following-outbreaks-of-cases-in-nigeria |access-date=2022-04-23 |website=ncdc.gov.ng |archive-date=15 April 2022 |archive-url=https://web.archive.org/web/20220415013226/https://www.ncdc.gov.ng/news/349/ncdc-intensifies-activities-for-lassa-fever-surveillance-and-response-following-outbreaks-of-cases-in-nigeria |url-status=live }}</ref>

====2022 outbreak====
The epidemic took a new form, from 3 to 30 January 2022, 211 laboratory confirmed Lassa fever cases including 40 deaths (case fatality ratio: 19%) have been cumulatively reported in 14 of the 36 Nigerian states and the Federal Capital Territory across the country.<ref>{{Cite web |title=Lassa Fever - Nigeria |url=https://www.who.int/emergencies/disease-outbreak-news/item/lassa-fever---nigeria |access-date=2022-04-23 |website=www.who.int |language=en |archive-date=16 February 2022 |archive-url=https://web.archive.org/web/20220216001642/https://www.who.int/emergencies/disease-outbreak-news/item/lassa-fever---nigeria |url-status=live }}</ref> In total from January until March, 132 deaths have been reported with a case fatality rate (CFR) of 19.1% which is lower than the CFR for the same period in 2021 (21.0%).<ref>{{Cite web |title=NCDC Lassa fever Situation Report Epi Week 13: 28 March - 3 April, 2022 - Nigeria |url=https://reliefweb.int/report/nigeria/ncdc-lassa-fever-situation-report-epi-week-13-28-march-3-april-2022 |access-date=2022-04-23 |website=ReliefWeb |date=17 April 2022 |language=en |archive-date=23 April 2022 |archive-url=https://web.archive.org/web/20220423082720/https://reliefweb.int/report/nigeria/ncdc-lassa-fever-situation-report-epi-week-13-28-march-3-april-2022 |url-status=live }}</ref>

====2024 outbreak====
In October 2024, a resident of [[Iowa]], United States, died from Lassa fever after traveling to West Africa. This case, confirmed by the [[Iowa Department of Health and Human Services]], underscores the risk of international spread. The individual likely contracted the virus abroad, as Lassa fever spreads through infected rodent excreta or bodily fluids. Health authorities are monitoring close contacts to prevent further transmission.<ref name="Branswell"/><ref>{{Cite web |last=CDC |date=2024-10-28 |title=Lassa Fever Suspected in Death of U.S. Traveler Returning from West Africa |url=https://www.cdc.gov/media/releases/2024/s1028-lassa-fever.html |access-date=2024-10-29 |website=CDC Newsroom |language=en-us}}</ref><ref>{{Cite web |last=ProLife HC |title=Lassa Fever Death in Iowa After West African Travel |url=https://prolifehc.com/post/Lassa-Fever-Death-in-Iowa-After-West-African-Travel |date=2024-10-29 |access-date=2024-10-29}}</ref>

====2025 outbreak====
Nigeria is grappling with a severe Lassa fever outbreak, reporting 535 confirmed cases and 98 deaths across 14 states since January, with a case fatality rate of 18.3%.<ref>{{Cite web |last=Anyaogu |first=Isaac |date=March 11, 2025 |title=Nigeria steps up fight against Lassa fever outbreak after 98 deaths this year |url=https://www.reuters.com/business/healthcare-pharmaceuticals/nigeria-steps-up-fight-against-lassa-fever-outbreak-after-98-deaths-this-year-2025-03-11/ |access-date=3 April 2025 |website=Reuters}}</ref> The disease spread to a patient who travelled to the UK, prompting contact tracing efforts in both countries. The Nigerian Centre for Disease Control (NCDC) issued a renewed advisory urging heightened awareness and preventative measures.

=== Liberia ===
Lassa fever is endemic in Liberia. From 1 January 2017 through 23 January 2018, 91 suspected cases were reported from six counties: Bong, Grand Bassa, Grand Kru, Lofa, Margibi, and Nimba. Thirty-three of these cases were laboratory confirmed, including 15 deaths (case fatality rate for confirmed cases = 45.4%).<ref>{{Cite web|url=https://www.who.int/csr/don/22-february-2018-lassa-fever-liberia/en/|archive-url=https://web.archive.org/web/20180222165208/http://www.who.int/csr/don/22-february-2018-lassa-fever-liberia/en/|url-status=dead|archive-date=22 February 2018|title=WHO {{!}} Lassa Fever – Liberia|website=WHO|access-date=2020-03-13}}</ref>

Liberia recorded 108 infections and 9 fatalities associated with 2018 Nigeria outbreak. The outbreak was concentrated in [[Lofa County|Lofa]] and [[Nimba County|Nimba]] Counties, where healthcare infrastructure was already fragile due to past epidemics. The Liberian Ministry of Health, supported by international partners, deployed mobile clinics and trained health workers to improve case detection and management.<ref>{{Cite web |title=Lassa Fever – Liberia |url=https://www.who.int/emergencies/disease-outbreak-news/item/22-february-2018-lassa-fever-liberia-en |access-date=2025-03-21 |website=www.who.int |language=en}}</ref>

In February 2020, a total of 24 confirmed cases with nine associated deaths has been reported from nine health districts in six counties. Grand Bossa and Bong counties account for 20 of the confirmed cases.<ref>{{Cite web|url=http://outbreaknewstoday.com/liberia-reports-increase-in-lassa-fever-45925/|title=Liberia reports increase in Lassa fever|date=2020-02-04|website=Outbreak News Today|language=en-US|access-date=2020-03-13|archive-date=5 March 2020|archive-url=https://web.archive.org/web/20200305061913/http://outbreaknewstoday.com/liberia-reports-increase-in-lassa-fever-45925/|url-status=live}}</ref>

===Other countries===
Sierra Leone reported 129 infections, with 12 deaths, in 2018. The outbreak was especially severe in Kenema and Bo Districts, where local health authorities struggled with limited resources. Public health officials launched community awareness initiatives to educate citizens about hygiene practices to prevent further spread.<ref>{{Cite web |title=Lassa Fever – The Netherlands (ex –Sierra Leone) |url=https://www.who.int/emergencies/disease-outbreak-news/item/2019-DON213 |access-date=2025-03-21 |website=www.who.int |language=en}}</ref>

Guinea experienced 98 cases and 8 fatalities, making it one of the least affected countries in the region in 2018. The outbreak was largely contained due to early intervention measures, including stringent border screenings and rapid response teams.<ref>{{Cite web |title=Lassa fever - Guinea |url=https://www.who.int/emergencies/disease-outbreak-news/item/2022-DON382 |access-date=2025-03-22 |website=www.who.int |language=en}}</ref><ref>{{Cite journal |last1=Keïta |first1=Mory |last2=Kizerbo |first2=Georges Alfred |last3=Subissi |first3=Lorenzo |last4=Traoré |first4=Fodé Amara |last5=Doré |first5=Ahmadou |last6=Camara |first6=Mohamed Fode |last7=Barry |first7=Ahmadou |last8=Pallawo |first8=Raymond |last9=Baldé |first9=Mamadou Oury |last10=Magassouba |first10=Nfaly |last11=Djingarey |first11=Mamoudou Harouna |last12=Fall |first12=Ibrahima Socé |date=2019-07-10 |title=Investigation of a cross-border case of Lassa fever in West Africa |journal=BMC Infectious Diseases |volume=19 |issue=1 |pages=606 |doi=10.1186/s12879-019-4240-8 |doi-access=free |issn=1471-2334 |pmc=6621975 |pmid=31291900}}</ref>