The first cases of Ebola virus infection were reported in Zaire (now known as the Democratic Republic of the Congo [DRC]) in 1976. There were 318 cases and 280 deaths, an 88% case fatality rate.[24]Report of an International Commission. Ebola haemorrhagic fever in Zaire, 1976. Bull World Health Organ. 1978;56(2):271-93.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2395567/pdf/bullwho00439-0113.pdf
http://www.ncbi.nlm.nih.gov/pubmed/307456?tool=bestpractice.com
Transmission in this outbreak was traced back to the use of contaminated needles in an outpatient clinic at Yambuku Mission Hospital. Since then, frequent outbreaks have occurred in Central and Western Africa.[25]Peterson AT, Bauer JT, Mills JN. Ecologic and geographic distribution of filovirus disease. Emerg Infect Dis. 2004 Jan;10(1):40-7.
https://wwwnc.cdc.gov/eid/article/10/01/03-0125_article
http://www.ncbi.nlm.nih.gov/pubmed/15078595?tool=bestpractice.com
The most common species of Ebola virus responsible for outbreaks is the Zaire ebolavirus, the second most common species being the Sudan ebolavirus.
The Zaire ebolavirus was responsible for the outbreak that started in West Africa in 2014 and finished in 2016. It was first reported in March 2014, and is the largest outbreak since the virus was first discovered in 1976. Genetic sequencing has shown that the virus isolated from infected patients in the 2014 outbreak is 97% similar to the virus that first emerged in 1976.[26]Centers for Disease Control and Prevention. CDC laboratories produce first genomic sequence of Liberian Ebola. August 2015 [internet publication].
https://www.cdc.gov/amd/stories/ebola.html
It is also responsible for smaller outbreaks in the DRC from 2017-2020. The Zaire ebolavirus has a reported case fatality rate of up to 90% in previous outbreaks.[4]Leroy EM, Gonzalez JP, Baize S. Ebola and Marburg haemorrhagic fever viruses: major scientific advances, but a relatively minor public health threat for Africa. Clin Microbiol Infect. 2011 Jul;17(7):964-76.
https://onlinelibrary.wiley.com/doi/10.1111/j.1469-0691.2011.03535.x/full
http://www.ncbi.nlm.nih.gov/pubmed/21722250?tool=bestpractice.com
Direct comparison of case fatality rates between different Ebola treatment centres and outbreaks should be interpreted with caution as many variables can introduce bias and skew even large cohort data. The case fatality rate during the 2014 outbreak was up to 64.3% in hospital admissions,[18]WHO Ebola Response Team. Ebola virus disease in West Africa: the first 9 months of the epidemic and forward projections. N Engl J Med. 2014 Oct 16;371(16):1481-95.
https://www.nejm.org/doi/full/10.1056/NEJMoa1411100#t=article
http://www.ncbi.nlm.nih.gov/pubmed/25244186?tool=bestpractice.com
falling to 31.5% in some treatment centres in West Africa,[27]Ansumana R, Jacobsen KH, Idris M, et al. Ebola in Freetown area, Sierra Leone - a case study of 581 patients. N Engl J Med. 2015 Feb 5;372(6):587-8.
https://www.nejm.org/doi/full/10.1056/NEJMc1413685
http://www.ncbi.nlm.nih.gov/pubmed/25539447?tool=bestpractice.com
and around 20% in patients managed outside West Africa.[28]New York Times. How many Ebola patients have been treated outside of Africa? January 2015 [internet publication].
https://www.nytimes.com/interactive/2014/07/31/world/africa/ebola-virus-outbreak-qa.html
In contrast to this, the Sudan ebolavirus has a lower case fatality rate of 53% to 65% in previous outbreaks, with the largest outbreak occurring in 2000 in Uganda (425 cases).[4]Leroy EM, Gonzalez JP, Baize S. Ebola and Marburg haemorrhagic fever viruses: major scientific advances, but a relatively minor public health threat for Africa. Clin Microbiol Infect. 2011 Jul;17(7):964-76.
https://onlinelibrary.wiley.com/doi/10.1111/j.1469-0691.2011.03535.x/full
http://www.ncbi.nlm.nih.gov/pubmed/21722250?tool=bestpractice.com
There has only been one outbreak of Bundibugyo ebolavirus: in 2007 in western Uganda, and this outbreak had a case fatality rate of 25%.[6]Roddy P, Howard N, Van Kerkhove MD, et al. Clinical manifestations and case management of Ebola haemorrhagic fever caused by a newly identified virus strain, Bundibugyo, Uganda, 2007-2008. PLoS One. 2012 Dec 28;7(12):e52986.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0052986
http://www.ncbi.nlm.nih.gov/pubmed/23285243?tool=bestpractice.com
Recent major outbreaks
2021: a new outbreak was reported in the DRC on 7 February 2021 in the North Kivu province. It is likely a resurgence of the outbreak that affected North Kivu, Ituri, and South Kivu provinces in 2018-2020.[29]World Health Organization. Disease outbreak news. Ebola virus disease – Democratic Republic of the Congo. 10 February 2021 [internet publication].
https://www.who.int/csr/don/10-february-2021-ebola-drc/en/
An outbreak was also reported in Guinea on 14 February 2021.[30]World Health Organization. Disease outbreak news. Ebola virus disease – Guinea. 17 February 2021 [internet publication].
https://www.who.int/csr/don/17-february-2021-ebola-gin/en/
2020: the eleventh outbreak in the DRC started on the 1st June in the Équateur province and was declared over on the 18th November, with a total of 130 cases and 55 deaths (case fatality rate 42%).[31]World Health Organization. Disease outbreak news: Ebola virus disease - Democratic Republic of the Congo. 18 November 2020 [internet publication].
https://www.who.int/csr/don/18-november-2020-ebola-drc/en/
2018-2020: the world’s second largest outbreak in the north Kivu and Ituri provinces of the DRC in 2018 was declared over on the 25th June 2020, with a total of 3481 cases and 2299 deaths (case fatality rate 66%).[32]World Health Organization. Ebola health update: north Kivu/Ituri, DRC, 2018-2020. July 2020 [internet publication].
https://www.who.int/emergencies/diseases/ebola/drc-2019
2018: small outbreak in the DRC with 54 cases and 33 deaths (case fatality rate 61%).[2]World Health Organization. Ebola virus disease fact sheet. February 2020 [internet publication].
https://www.who.int/mediacentre/factsheets/fs103/en/
2014-2016: the world’s largest outbreak started in the DRC in 2014 and finished in 2016, with over 28,000 cases and 11,000 deaths (case fatality rate 46%).[2]World Health Organization. Ebola virus disease fact sheet. February 2020 [internet publication].
https://www.who.int/mediacentre/factsheets/fs103/en/
WHO: Ebola outbreaks
external link opens in a new window
The WHO declares an outbreak is over when no confirmed or probable cases are detected for a period of 42 days (i.e., twice the maximum incubation period) since the last potential exposure to the last case occurred; however, WHO recommends heightened surveillance and response activities during the 42-day period and for at least 6 months after.[33]World Health Organization. WHO recommended criteria for declaring the end of the Ebola virus disease. 4 March 2020 [internet publicaton].
https://www.who.int/publications/m/item/who-recommended-criteria-for-declaring-the-end-of-the-ebola-virus-disease-outbreak