Ebola outbreaks have been restricted to Africa, with the exception of Reston ebolavirus. The International Committee on Taxonomy of Viruses currently recognizes four species of the Ebola: Zaire virus (ZEBOV), Sudan ebolavirus (SEBOV), Reston ebolavirus (REBOV), and Cote d'Ivoire ebolavirus (CIEBOV).[1] One additional species or type of Ebola is often recognized by the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC) as Bundibugyo ebolavirus or Ebola-Bundibugyo, following the outbreak in Uganda in 2007.[2][3][4]
Transmission between natural reservoirs and humans is rare, and outbreaks are often traceable to a single index case where an individual has handled the carcass of a gorilla, chimpanzee, or duiker.[5] The virus then spreads person-to-person, especially within families, hospitals, and during some mortuary rituals where contact among individuals becomes more likely.[6] Before outbreaks are confirmed in areas of weak surveillance on the local or regional levels, Ebola is often mistaken for malaria, typhoid fever, dysentery, influenza, or various bacterial infections which may be endemic to the region. Learning from failed responses, such as that to the 2000 Uganda outbreak, public health measures including the WHO's Global Outbreak and Response Network were instituted in areas at high risk. Field laboratories were established in order to confirm cases, instead of shipping samples to South Africa.[7]
The United States Centers for Disease Control and Prevention Special Pathogens Branch charter to study highly infectious viruses, many causing hemorrhagic fevers, has historically endowed it to closely follow Ebola outbreaks.[8] Compiling scientific journals and public health announcements, the following list is from Known Cases and Outbreaks of Ebola Hemorrhagic Fever, in Chronological Order:[9]
| Year | Country | Type | Reported human cases | Reported deaths | % Fatality | Description |
|---|---|---|---|---|---|---|
| 1976 | Zaire (Democratic Republic of Congo) | ZEBOV | 318 | 280 | 88% | Occurred in Yambuku and surrounding area. Disease was spread by close personal contact and by use of contaminated needles and syringes in hospitals/clinics. This outbreak was the first recognition of the disease.[10] |
| 1976 | Sudan | SEBOV | 284 | 151 | 53% | Occurred in Nzara, Maridi and the surrounding area. Disease was spread mainly through close personal contact within hospitals. Many medical care personnel were infected.[11] |
| 1976 | England | SEBOV | 1 | 0 | 0% | Laboratory infection by accidental stick of contaminated needle.[12] |
| 1977 | Zaire | ZEBOV | 1 | 1 | 100% | Noted retrospectively in the village of Tandala.[13] |
| 1979 | Sudan | SEBOV | 34 | 22 | 65% | Occurred in Nzara, Maridi. Recurrent outbreak at the same site as the 1976 Sudan epidemic.[14] |
| 1989 | USA | REBOV | 0 | 0 | 0% | REBOV was introduced into quarantine facilities in Virginia and Pennsylvania by monkeys imported from the Philippines.[15] |
| 1990 | USA | REBOV | 4 (asymptomatic) | 0 | 0% | REBOV was introduced once again into quarantine facilities in Virginia and Texas by monkeys imported from the Philippines. Four humans developed antibodies but did not get sick.[16] |
| 1989-1990 | Philippines | REBOV | 3 (asymptomatic) | 0 | 0% | High mortality among cynomolgus macaques in a primate facility responsible for exporting animals in the USA.[17] Three workers in the animal facility developed antibodies but did not get sick.[18] |
| 1992 | Italy | REBOV | 0 | 0 | 0% | REBOV was introduced into quarantine facilities in Siena by monkeys imported from the same export facility in the Philippines that was involved in the episodes in the United States. No humans were infected.[19] |
| 1994 | Gabon | ZEBOV | 52 | 31 | 60% | Occurred in Mékouka and other gold-mining camps deep in the rain forest. Initially thought to be yellow fever; identified as Ebola hemorrhagic fever in 1995.[20] |
| 1994 | Ivory Coast | CIEBOV | 1 | 0 | 0% | Scientist became ill after conducting an autopsy on a wild chimpanzee in the Tai Forest. The patient was treated in Switzerland.[21] |
| 1995 | Democratic Republic of Congo (formerly Zaire) | ZEBOV | 315 | 250 | 81% | Occurred in Kikwit and surrounding area. Traced to index case-patient who worked in forest adjoining the city. Epidemic spread through families and hospitals.[22] |
| 1996 Jan-Apr | Gabon | ZEBOV | 37 | 21 | 57% | Occurred in Mayibout area. A chimpanzee found dead in the forest was eaten by people hunting for food. Nineteen people who were involved in the butchery of the animal became ill; other cases occurred in family members.[20] |
| 1996-1997 Jul-Jan | Gabon | ZEBOV | 60 | 45 | 74% | Occurred in Booué area with transport of patients to Libreville. Index case-patient was a hunter who lived in a forest camp. Disease was spread by close contact with infected persons. A dead chimpanzee found in the forest at the time was determined to be infected.[20] |
| 1996 | South Africa | ZEBOV | 2 | 1 | 50% | A medical professional traveled from Gabon to Johannesburg, South Africa, after having treated Ebola virus-infected patients and thus having been exposed to the virus. He was hospitalized, and a nurse who took care of him became infected and died.[23] |
| 1996 | USA | REBOV | 0 | 0 | 0% | REBOV was introduced into a quarantine facility in Texas by monkeys imported from the Philippines. No human infections were identified.[24] |
| 1996 | Philippines | REBOV | 0 | 0 | 0% | REBOV was identified in a monkey export facility in the Philippines. No human infections were identified.[25] |
| 2000-2001 | Uganda | SEBOV | 425 | 224 | 53% | Occurred in Gulu, Masindi, and Mbarara districts of Uganda. The three most important risks associated with Ebola virus infection were attending funerals of Ebola hemorrhagic fever case-patients, having contact with case-patients in one's family, and providing medical care to Ebola case-patients without using adequate personal protective measures.[26] |
| 2001-2002 Oct-Mar | Gabon | ZEBOV | 65 | 53 | 82% | Outbreak occurred over the border of Gabon and the Republic of the Congo.[27] |
| 2001-2002 Oct-Mar | Republic of Congo | ZEBOV | 57 | 43 | 75% | Outbreak occurred over the border of Gabon and the Republic of the Congo. This was the first time that Ebola hemorrhagic fever was reported in the Republic of the Congo.[27] |
| 2002-2003 Dec-Apr | Republic of Congo | ZEBOV | 143 | 128 | 89% | Outbreak occurred in the districts of Mbomo and Kéllé in Cuvette Ouest Département.[28] |
| 2003 Nov-Dec | Republic of Congo | ZEBOV | 35 | 29 | 83% | Outbreak occurred in Mbomo and Mbandza villages located in Mbomo district, Cuvette Ouest Département.[29] |
| 2004 | Sudan | SEBOV | 17 | 7 | 41% | Outbreak occurred in Yambio county of southern Sudan. This outbreak was concurrent with an outbreak of measles in the same area, and several suspected EHF cases were later reclassified as measles cases.[30] |
| 2007 | Democratic Republic of Congo | ZEBOV | 264 | 187 | 71% | Outbreak occurred in Kasai Occidental Province. The outbreak was declared over on November 20. Last confirmed case on October 4 and last death on October 10.[31] |
| 2007-2008 Dec-Jan | Uganda | Bundibugyo ebolavirus | 149 | 37 | 25% | Outbreak occurred in Bundibugyo District in western Uganda. First reported occurrence of a new strain.[2][3][4] |
| 2008 Nov | Philippines | REBOV | 6 (asymptomatic) | 0 | 0% | First known occurrence of REBOV in pigs. Strain closely similar to earlier strains. Six workers from the pig farm and slaughterhouse developed antibodies but did not become sick.[32][33] |
| 2008-2009 Dec-Feb | Democratic Republic of Congo | ZEBOV | 32 | 14 | 47% | Outbreak occurred in the Mweka and Luebo health zones of the Province of Kasai Occidental.[34] |