Ebola virus, Filoviridae family, is comprised of four distinct subtypes: Zaïre, Sudan, Côte d'Ivoire and Reston. Three subtypes, occurring in the Democratic Republic of the Congo (formerly Zaire), Sudan and Côte d'Ivoire, have been identified as causing illness in humans. Ebola haemorrhagic fever (EHF) is a febrile haemorrhagic illness which causes death in 50-90% of all clinically ill cases. Human infection with the Ebola Reston subtype, found in the Western Pacific, has only caused asymptomatic illness, meaning that those who contract the disease do not experience clinical illness. The natural reservoir of the Ebola virus seems to reside in the rain forests of the African continent and in areas of the Western Pacific .
Ebola outbreak chronology
The Ebola virus is transmitted by direct contact with the blood, secretions, organs or other bodily fluids of infected persons.
Burial ceremonies where mourners have direct contact with the body of the deceased person can play a significant role in the transmission of Ebola.
The infection of human cases with Ebola virus has been documented through the handling of infected chimpanzees, gorillas, and forest antelopes--both dead and alive--as was documented in Côte d'Ivoire, the Republic of Congo and Gabon. The transmission of the Ebola Reston strain through the handling of cynomolgus monkeys has also been reported.
Health care workers have frequently been infected while treating Ebola patients, through close contact without the use of correct infection control precautions and adequate barrier nursing procedures.
Incubation period: two to 21 days.
Ebola is often characterized by the sudden onset of fever, intense weakness, muscle pain, headache and sore throat. This is often followed by vomiting, diarrhoea, rash, impaired kidney and liver function, and in some cases, both internal and external bleeding. Laboratory findings show low counts of white blood cells and platelets as well as elevated liver enzymes.
Specialized laboratory tests on blood specimens detect specific antigens and/or genes of the virus. Antibodies to the virus can be detected, and the virus can be isolated in cell culture. Tests on samples present an extreme biohazard risk and are only conducted under maximum biological containment conditions. New developments in diagnostic techniques include non-invasive methods of diagnosis (testing saliva and urine samples) and testing inactivated samples to provide rapid laboratory diagnosis to support case management during outbreak control activities.
Therapy and vaccine
Severe cases require intensive supportive care, as patients are frequently dehydrated and in need of intravenous fluids or oral rehydration with solutions containing electrolytes.
No specific treatment or vaccine is yet available for Ebola haemorrhagic fever. Several vaccine candidates are being tested but it could be several years before any are available. A new drug therapy has shown early promise in laboratory studies and is currently being evaluated further. However, this too will take several years.
Experimental studies involving the use of hyper-immune sera on animals have demonstrated no protection against the disease.
Suspected cases should be isolated from other patients and strict barrier nursing techniques implemented.
Contact tracing and follow-up of people who may have been exposed to Ebola through close contact with other cases is essential.
All hospital personnel should be briefed on the nature of the disease and its routes of transmission. Particular emphasis should be placed on ensuring that invasive procedures such as the placing of intravenous lines and the handling of blood, secretions, catheters and suction devices are carried out under strict barrier nursing conditions. Hospital staff should have individual gowns, gloves, masks and goggles. Non-disposable protective equipment must not be reused unless they have been properly disinfected.
Infection may also be spread through contact with the soiled clothing or bed linens from a patient with Ebola. Disinfection is therefore required before handling these items.
Communities affected by Ebola should make efforts to ensure that the population is well informed, both about the nature of the disease itself and about necessary outbreak containment measures, including burial of the deceased. People who have died from Ebola should be promptly and safely buried.
As the primary mode of person-to-person transmission is contact with contaminated blood, secretions or body fluids, any person who has had close physical contact with patients should be kept under strict surveillance, i.e. body temperature checks twice a day, with immediate hospitalization and strict isolation recommended in case of the onset of fever.
Hospital personnel who come into close contact with patients or contaminated materials without barrier nursing attire must be considered as contacts and followed up accordingly.
The Ebola virus was first identified in a western equatorial province of Sudan and in a nearby region of Zaïre (now the Democratic Republic of the Congo) in 1976 after significant epidemics in Yambuku, northern Democratic Republic of the Congo, and Nzara, southern Sudan.
Between June and November 1976, the Ebola virus infected 284 people in Sudan, causing 151 deaths. In the Democratic Republic of the Congo, there were 318 cases and 280 deaths in September and October. An isolated case occurred in the Democratic Republic of the Congo in 1977, and there was another outbreak in Sudan in 1979 (33 cases, including 22 deaths).
In 1989, an Ebola virus subtype Reston, was isolated in quarantined laboratory cynomolgus monkeys (Macacca fascicularis) in Reston, Virginia, USA. From 1989 to 1996, several outbreaks caused by the Ebola Reston subtype occurred in monkeys imported from the Philippines to the USA (Reston in Virginia, Alice in Texas and Pennsylvania) and to Italy. Investigations traced the source of all Ebola Reston outbreaks to one export facility near Manila in the Philippines, but the mode of contamination of this facility was not determined. Several monkeys died, and at least four people were infected, although none of them suffered clinical illness.
One human case of Ebola haemorrhagic fever of the Cote d'Ivoire subtype and several cases in chimpanzees were confirmed in Côte d'Ivoire in November 1994.
A large epidemic occurred in Kikwit, the Democratic Republic of the Congo in 1995 with 315 cases, 244 of which had fatal outcomes.
In Gabon, Ebola haemorrhagic fever was first documented in 1994 (19 cases including 9 deaths). Successive outbreaks occurred in February (37 cases including 21 deaths) and July of 1996 (60 cases including 45 deaths).
In October 2000, Ebola was reported in Gulu district in northern Uganda. Between September 2000 and January 2001, the Sudan subtype of the Ebola virus infected 425 cases, including 224 deaths, making this the largest epidemic so far documented of Ebola. This was the first reported emergence of the Sudan Ebola virus since 1979.
From October 2001 to December 2003, several EHF outbreaks of the Zaïre subtype, were reported in Gabon and the Republic of Congo with a total of 302 cases and 254 deaths: Mékambo-Mbomo-Kéllé 2001-2002, Kéllé-Mbomo 2003 and Mbandza-Mbomo 2003.
Approximately 1,850 cases with over 1,200 deaths have been documented since the Ebola virus was discovered.
The natural reservoir of the Ebola virus is unknown despite extensive studies, but seems to reside in the rain forests on the African continent and in the Western Pacific.
Although non-human primates have been a source of infection for humans, they are not thought to be the reservoir. They, like humans, are believed to be infected directly from the natural reservoir or through a chain of transmission from the natural reservoir.
On the African continent, Ebola infections of human cases have been linked to direct contact with gorillas, chimpanzees, monkeys, forest antelope and porcupines found dead in the rainforest. So far, the Ebola virus has been detected in the wild in carcasses of chimpanzees (in Côte-d'Ivoire and Republic of Congo), gorillas (Gabon and Republic of Congo) and duikers (Republic of Congo).
Different hypotheses have been developed to try to explain the origin of Ebola outbreaks. Laboratory observation has shown that bats experimentally infected with Ebola do not die, and this has raised speculation that these mammals may play a role in maintaining the virus in the tropical forest.
Extensive ecological studies are underway in the Republic of Congo and Gabon to identify the Ebola's natural reservoir.