Ebola epidemiology and demographics

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Michael Maddaleni, B.S.; Guillermo Rodriguez Nava, M.D. [2]

Overview

Outbreaks of Ebola have been generally restricted to Africa. Governments and individuals should quickly quarantine the area. Lack of roads and transportation helps to contain the outbreak in remote areas. The potential for widespread Ebola virus disease epidemics is considered low due to the high case-fatality rate, the rapidity of demise of patients, and the often remote areas where infections occur.

Cases of Ebola in Africa

Cases of Ebola Hemorrhagic Fever in Africa, 1976 - 2014 Country Town Cases Deaths Species Year Dem. Rep. of Congo Yambuku 318 280 Zaire ebolavirus 1976 South Sudan Nzara 284 151 Sudan ebolavirus 1976 Dem. Rep. of Congo Tandala 1 1 Zaire ebolavirus 1977 South Sudan Nzara 34 22 Sudan ebolavirus 1979 Gabon Mekouka 52 31 Zaire ebolavirus 1994 Ivory Coast Tai Forest 1 0 Taï Forest ebolavirus 1994 Dem. Rep. of Congo Kikwit 315 250 Zaire ebolavirus 1995 Gabon Mayibout 37 21 Zaire ebolavirus 1996 Gabon Booue 60 45 Zaire ebolavirus 1996 South Africa Johannesburg 2 1 Zaire ebolavirus 1996 Uganda Gulu 425 224 Zaire ebolavirus 2000 Gabon Libreville 65 53 Zaire ebolavirus 2001 Republic of Congo Not specified 57 43 Zaire ebolavirus 2001 Republic of Congo Mbomo 143 128 Zaire ebolavirus 2002 Republic of Congo Mbomo 35 29 Zaire ebolavirus 2003 South Sudan Yambio 17 7 Zaire ebolavirus 2004 Dem. Rep. of Congo Luebo 264 187 Zaire ebolavirus 2007 Uganda Bundibugyo 149 37 Bundibugyo ebolavirus 2007 Dem. Rep. of Congo Luebo 32 15 Zaire ebolavirus 2008 Uganda Luwero District 1 1 Sudan ebolavirus 2011 Uganda Kibaale District 11* 4* Sudan ebolavirus 2012 Dem. Rep. of Congo Isiro Health Zone 36* 13* Bundibugyo ebolavirus 2012 Uganda Luwero District 6* 3* Sudan ebolavirus 2012 Guinea, Sierra Leone, Liberia multiple 362* ? Zaire ebolavirus 2014 *Numbers reflect laboratory confirmed cases only.

Ebola Hemorrhagic Fever Distribution Map. Adapted from Centers for Disease Control and Prevention

Outbreaks

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).

Known Cases and Outbreaks of Ebola Hemorrhagic Fever, in Chronological Order

Year(s)	Country	Ebola subtype	Reported number of human cases	Reported number (%) of deaths among cases	Situation
1976	Zaire (Democratic Republic of the Congo - DRC)	Ebola virus	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.
1976	Sudan (South Sudan)	Sudan virus	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.
1976	England	Sudan virus	1	0	Laboratory infection by accidental stick of contaminated needle.
1977	Zaire	Ebola virus	1	1 (100%)	Noted retrospectively in the village of Tandala.
1979	Sudan (South Sudan)	Sudan virus	34	22 (65%)	Occured in Nzara, Maridi. Recurrent outbreak at the same site as the 1976 Sudan epidemic.
1989	USA	Reston virus	0	0	Ebola-Reston virus was introduced into quarantine facilities in Virginia and Pennsylvania by monkeys imported from the Philippines.
1990	USA	Reston virus	4 (asymptomatic)	0	Ebola-Reston virus 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.
1989-1990	Philippines	Reston virus	3 (asymptomatic)	0	High mortality among cynomolgus macaques in a primate facility responsible for exporting animals in the USA. Three workers in the animal facility developed antibodies but did not get sick.
1992	Italy	Reston virus	0	0	Ebola-Reston virus was introduced into quarantine facilities in Sienna 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.
1994	Gabon	Ebola virus	52	31 (60%)	Occured 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.
1994	Ivory Coast	Taï Forest virus	1	0	Scientist became ill after conducting an autopsy on a wild chimpanzee in the Tai Forest. The patient was treated in Switzerland.
1995	Democratic Republic of the Congo (formerly Zaire)	Ebola virus	315	250 (81%)	Occured in Kikwit and surrounding area. Traced to index case-patient who worked in forest adjoining the city. Epidemic spread through families and hospitals.
1996 (January-April)	Gabon	Ebola virus	37	21 (57%)	Occured 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 occured in family members.
1996-1997 (July-January)	Gabon	Ebola virus	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.
1996	South Africa	Ebola virus	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.
1996	USA	Reston virus	0	0	Ebola-Reston virus was introduced into a quarantine facility in Texas by monkeys imported from the Philippines. No human infections were identified.
1996	Philippines	Reston virus	0	0	Ebola-Reston virus was identified in a mokey export facility in the Philippines. No human infections were identified.
1996	Russia	Ebola virus	1	1 (100%)	Laboratory contamination
2000-2001	Uganda	Sudan virus	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.
October 2001-March 2002	Gabon	Ebola virus	65	53 (82%)	Outbreak occured over the border of Gabon and the Republic of the Congo.
October 2001-March 2002	Republic of Congo	Ebola virus	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.
v December 2002-April 2003	Republic of Congo	Ebola virus	143	128 (89%)	Outbreak occurred in the districts of Mbomo and Kéllé in Cuvette Ouest Département.
November-December 2003	Republic of Congo	Ebola virus	35	29 (83%)	Outbreak occured in Mbomo and Mbandza villages located in Mbomo distric, Cuvette Ouest Département.
2004	Sudan (South Sudan)	Sudan virus	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 measeles cases.
2004	Russia	Ebola virus	1	1 (100%)	Laboratory contamination.
2007	Democratic Republic of Congo	Ebola virus	264	187 (71%)	Outbreak occurred in Kasai Occidental Province. The outbreak was declared over November 20. Last confirmed case on October 4 and last death on October 10.
December 2007-January 2008	Uganda	Bundibugyo virus	149	37 (25%)	Outbreak occurred in Bundibugyo District in western Uganda. First reported occurance of a new strain.
November 2008	Philippines	Reston virus	6 (asymptomatic)	0	First known occurrence of Ebola-Reston in pigs. Strain closely similar to earlier strains. Six workers from the pig farm and slaughterhouse developed antibodies but did not become sick.
December 2008-February 2009	Democratic Republic of the Congo	Ebola virus	32	15 (47%)	Outbreak occurred in the Mweka and luebo health zones of the Province of Kasai Occidental.
May-11	Uganda	Sudan virus	1	1 (100%)	The Ugandan Ministry of Health informed the public that a patient with suspected Ebola Hemorrhagic fever died on May 6, 2011 in the Luwero district, Uganda. The quick diagnosis from a blood sample of Ebola virus was provided by the new CDC Viral Hemorrhagic Fever laboratory installed at the Uganda Viral Research Institute (UVRI).
June-October 2012	Uganda	Sudan virus	11*	4* (36.4%)	Outbreak occurred in the Kibaale District of Uganda. Laboratory tests of blood samples were conducted by the UVRI and the U.S. Centers for Disease Control and Prevention (CDC).
June-November 2012	Democratic Republic of the Congo	Bundibugyo virus	36*	13* (36.1%)	Outbreak occurred in DRC’s Province Orientale. Laboratory support was provided through CDC and the Public Health Agency of Canada (PHAC)’s field laboratory in Isiro, and through the CDC/UVRI lab in Uganda. The outbreak in DRC has no epidemiologic link to the near contemporaneous Ebola outbreak in the Kibaale district of Uganda.
November 2012-January 2013	Uganda	Sudan virus	6*	3* (50%)	Outbreak occurred in the Luwero District. CDC assisted the Ministry of Health in the epidemiologic and diagnostic aspects of the outbreak. Testing of samples by CDC's Viral Special Pathogens Branch occurred at UVRI in Entebbe.
March 2014-Present	Guinea, Liberia, and Sierra Leone	Ebola virus	362*	?	Ongoing outbreak across Guinea, northern Liberia, and now eastern Sierra Leone. Numbers of patients is constantly evolving due to the on-going investigation.
* Numbers reflect laboratory confirmed cases only.

West Africa outbreak

First affected Districts in Guinea and neighboring areas.
Image extracted from WHO: Ebola Hemorrhagic Fever in Guinea

Distribution of confirmed and suspected cases as of 16 June 2014.
Image extracted from WHO: Ebola Virus Disease (EVD) in West Africa (situation as of 16 June 2014)

On March 23, 2014, the Ministry of Health of Guinea notified the World Health Organization (WHO) of a rapidly evolving outbreak of Ebola virus disease (EVD) in forested areas south eastern Guinea: Guekedou, Macenta, Nzerekore and Kissidougou districts. As of 22 March, 2014, a total of 49 cases including 29 deaths (case fatality ratio: 59%) were reported. Four health care workers were among the victims. At the same time, suspected cases in border areas of Liberia and Sierra Leone were being investigated. Six blood samples were tested at Institut Pasteur in Lyon, France, resulting positive for Ebola virus by PCR, confirming the first Ebola virus disease outbreak in Guinea. Preliminary results from sequencing of a part of the L gene showed strong homology with Zaire Ebolavirus. The ministry of health together with the WHO and other partners initiated measures to control the outbreak and prevent further spread. Médecins Sans Frontières, Switzerland (MSF-CH) started working in the affected areas and assisted with the establishment of isolation facilities, and also supported transport of the biological smaples from suspected cases and contacts to international reference laboratories for urgent testing. The Emerging and Dangerous Pathogens Laboratory Network (EDPLN) worked with the Guinean VHF Laboratory in Donka, the Institut Pasteur in Lyon, the Institut Pasteur in Dakar, and the Kenema Lassa fever laboratory in Sierra Leone to make available appropriate Filovirus diagnostic capacity in Guinea and Sierra Leone.

On 30 March, 2014, the Ministry of Health of Liberia provided updated details on the suspected and confirmed cases of Ebola virus disease in Liberia. As of 29 March, seven clinical samples, all from adult patients from Foya district, Lofa County, were tested by PCR using Ebola Zaire virus primers by the mobile laboratory of the Institut Pasteur (IP) Dakar in Conakry. Two of those samples tested positive for the ebolavirus. There were 2 deaths among the suspected cases; a 35 year-old woman who died on 21 March tested positive for ebolavirus while a male patient who died on 27 March tested negative. At that time, Foya was the only district in Liberia that reported confirmed or suspected cases of Ebola Hemorrhagic Fever. As of 26 March, Liberia had 27 contacts under medical follow-up. Liberia established a high level National Task Force to lead the response. Response partners include WHO, the International Red Cross (IRC), Samaritan’s Purse (SP) Liberia, Pentecostal Mission Unlimited (PMU)-Liberia, CHF-WASH Liberia, PLAN-Liberia, UNFPA and UNICEF.

On 3 April, 2014, the outbreak was confirmed to be caused by a strain of ebolavirus with very close homology (98%) to the Zaire ebolavirus. This is the first time the disease has been detected in West Africa.

As of 17 June 2014, in Guinea a total of 7 new cases and 5 new deaths were reported from Gueckedou (4 cases and 5 deaths) and Boffa (3 cases and 0 deaths). This brings the cumulative number of cases and deaths reported from Guinea to 398 (254 confirmed, 88 probable and 56 suspected) and 264 deaths. The geographical distribution of these cases and deaths is as follows: Conakry (70 cases and 33 deaths); Guéckédou (224 cases and 173 deaths); Macenta (41 cases and 28 deaths); Dabola, (4 cases and 4 deaths); Kissidougou (8 cases and 5 deaths); Dinguiraye (1 case and 1 death); Telimele (30 cases and 9 deaths); Bofa (19 cases and 10 deaths) and Kouroussa (1 case and 1 death). Twenty four (24) patients are currently in EVD Treatment Centres: Conakry (6), Guéckédou (9), Telimele (3) and Boffa (6). The number of contacts currently being followed countrywide is 1,258 and distributed as follows: Conakry (252), Guéckédou (529), Macenta (52), Telimele (118), Dubreka (118) and Boffa (189). So far 69.4% (2,848 contacts being followed-up out of a 4,106 contacts registered since the beginning of the outbreak) have completed the mandatory 21 days observation period.

In Liberia a total of 9 new cases and 5 new deaths were reported from Lofa (6 cases and 0 death) and Montserado (3 cases and 5 deaths). This brings the cumulative number of cases and deaths reported from Liberia to 33 (18 confirmed, 8 probable and 7 suspected) and 24 deaths. The geographical distribution of these cases and deaths is as follows: Lofa (21 cases and 14 deaths); Montserado (8 cases and 8 deaths); Margibi (2 cases and 2 deaths) and Nimba (2 cases and 0 death). Five (5) patients are currently in EVD Treatment Centres in Lofa. The number of contacts currently being followed countrywide is 108 and distributed as follows: Lofa (95), Montserado (13). So far 41.5% (108 contacts being followed-up out of a 260 contacts registered since the beginning of the outbreak) have completed the mandatory 21 days observation period.

In Sierra Leone a total of 31 new cases and 4 new deaths were reported from Kailahun (29 cases and 4 deaths), Kono (1 case) and Western (1 case). This brings the cumulative number of cases and deaths reported from Sierra Leone to 97 (92 confirmed, 3 probable and 2 suspected) and 49 deaths. The geographical distribution of these cases and deaths is as follows: Kailahun (92 cases and 46 deaths); Kambia (1 cases and 0 deaths); Port Loko (2 cases and 1 deaths); Kono, (1 case and 0 death) and Western (1 cases and 1 death. Thirty three (33) patients are currently in EVD Treatment Centre of Kenema. The number of contacts currently being followed countrywide is 37 from Kailahun. Contact listing is continuing in Kailahun, Kambia and Port Loko.

Democratic Republic of the Congo

As of August 30, 2007, 103 people (100 adults and three children) were infected by a suspected hemorrhagic fever outbreak in the village of Mweka, Democratic Republic of the Congo (DRC). The outbreak started after the funerals of two village chiefs, and 217 people in four villages fell ill. The World Health Organization sent a team to take blood samples for analysis and confirmed that many of the cases are the result of the Ebola virus . The Congo's last major Ebola epidemic killed 245 people in 1995 inKikwit, about 200 miles from the source of the Aug. 2007 outbreak.

On November 30, 2007, the Uganda Ministry of Health confirmed an outbreak of Ebola in the Bundibugyo District. After confirmation of samples tested by the United States National Reference Laboratories and the Centers for Disease Control, the World Health Organization confirmed the presence of a new species of the Ebola virus. The epidemic came to an official end on February 20, 2008. 149 cases of this new strain were reported and 37 of those led to deaths.

Uganda Outbreak

On October 8, 2000, an outbreak of an unusual febrile illness with occasional hemorrhage and significant mortality was reported to the Ministry of Health (MoH) in Kampala by the superintendent of St. Mary's Hospital in Lacor, and the District Director of Health Services in the Gulu District. A preliminary assessment conducted by MoH found additional cases in Gulu District and in Gulu Hospital, the regional referral hospital. On October 15, suspicion of Ebola hemorrhagic fever (EHF) was confirmed when the National Institute of Virology (NIV), Johannesburg, South Africa, identified Ebola virus infection among specimens from patients, including health-care workers at St. Mary's Hospital. This report describes surveillance and control activities related to the EHF outbreak and presents preliminary clinical and epidemiologic findings.

Control activities were organized around surveillance and epidemiology, clinical case management, social education and mobilization, and coordination and logistic support. An active EHF surveillance system was initiated to determine the extent and magnitude of the outbreak, identify foci of disease activity, and detect cases early. Ill persons were encouraged to be assessed at a hospital and, if indicated, to be hospitalized to reduce further community transmission. Targeted prevention activities included follow-up of contacts of identified cases for 21 days; establishment of trained burial teams for all potential and confirmed EHF deaths; community education; cessation of traditional healing and burial practices; cessation of large public gatherings; and updates of hospital infection-control measures, including isolation wards. Laboratory testing was performed at a field laboratory established at St. Mary's Hospital by CDC and supplemented by additional testing at CDC and NIV. Sequence analysis revealed that the virus associated with this outbreak was Ebola-Sudan and differed at the nucleotide sequence level from earlier Ebola-Sudan isolates by 3.3% and 4.2% in the polymerase (362 nucleotides sequenced) and nucleocapsid (146 nucleotides sequenced) protein encoding genes, respectively.

During the third week of October, active surveillance was established and included three case notification categories: alert, suspect, and probable. The alert category comprised persons with sudden onset of high fever, sudden death, or hemorrhage, and was used by community members to alert health-care personnel. The suspect category comprised persons with fever and contact with a potential case-patient; persons with unexplained bleeding; persons with fever and three or more specified symptoms (i.e., headache, vomiting, anorexia, diarrhea, weakness or severe fatigue, abdominal pain, body aches or joint pains, difficulty swallowing, difficulty breathing, and hiccups), and all unexplained deaths. The suspect category was used by mobile surveillance teams to determine whether a patient required transport to an isolation ward. The probable category included persons who met these criteria and were assessed and reported by a physician. Laboratory tests included virus antigen detection and antibody ELISA tests and reverse transcriptase polymerase chain reaction. Laboratory-confirmed case-patients were defined as patients who met the surveillance case definitions and were either positive for Ebola virus antigen or Ebola IgG antibody.

During October 5--November 27, among 62 persons with laboratory-confirmed EHF admitted to Gulu Hospital, symptoms included diarrhea (66%), asthenia(64%),anorexia (61%), headache (63%), nausea and vomiting (60%), abdominal pain (55%), and chest pain (48%). Patients presented for care a mean of 8 days (range: 2--20 days) after symptom onset. Bleeding occurred in 12 (20%) patients and primarily involved the gastrointestinal tract. Among the 62 confirmed case-patients, 36 (58%) died; among patients aged <15 years, four of five died (case fatality: 80%). Spontaneous abortions were reported among pregnant women infected with EHF. Patients who died usually exhibited a rapid progression of shock, increasing coagulopathy, and loss ofconsciousness.

As of January 23, 2001, 425 presumptive* case-patients with 224 (53%) deaths attributed to EHF were recorded from three districts in Uganda: 393 (93%) from Gulu, 27 (6%) from Masindi, and five (1%) from Mbarara. The combined area comprises approximately 11,700 square miles (31,000 square kilometers; 2000 combined population: 1.8 million) (See the map of Uganda below) (1). Although the cluster of cases in early October triggered identification of the outbreak and response measures, investigations (i.e., case-record review and interviews with surviving patients or their surrogates) identified cases occurring in the community and patients hospitalized several weeks earlier. The onset of illness of the earliest presumptive case was August 30, 2000, and onset of last presumptive case was January 9, 2001 (See the graph below the map of Uganda). The ages of presumptive case-patients ranged from 3 days--72 years (median: 28 years); 269 (63%) were women. Mean time from symptom onset to death was 8 days (95% confidence interval=±5 days); 218 (51%) presumptive cases were laboratory confirmed.

Epidemiologic investigations identified the three most important means of transmission as attending funerals of presumptive EHF case-patients where ritual contact with the deceased occurred, and intrafamilial or nosocomial transmission. Fourteen (64%) of 22 health-care workers in Gulu were infected after establishing the isolation wards; these incidences led to the reinforcement of infection-control measures. Two distant focal outbreaks were initiated by movement of infected contacts of EHF cases from Gulu to Mbarara and Masindi districts. National notification and surveillance efforts led to the rapid identification of these foci and effective containment.

Distribution of presumptive case-patients with Ebola hemorrhagic fever-Uganda August 2000-January 2001Adapted from Centers for Disease Control and Prevention.

Number of presumptive case-patients with Ebola hemorrhagic fever, by week of onset - Uganda, August 2000-January 2001Adapted from Centers for Disease Control and Prevention.

Distribution

This is a map of the distribution of ebola in Africa.

Distribution of Ebola and Marburg virus in Africa (note that integrated genes from filoviruses have been detected in mammals from the New World as well). (A) Known points of filovirus disease. Projected distribution of ecological niche of: (B) all filoviruses, (C) ebolaviruses, (D) marburgviruses.