Ebola haemorrhagic fever is a severe disease caused by a virus of the filovirus family, which occurs in humans and other primates. The disease emerged in 1976 in almost simultaneous outbreaks in the Democratic Republic of the Congo (DRC) and Sudan. Ebola then disappeared after 1979 and was not recognized again until 1994, and outbreaks have been occurring with increasing frequency since. The largest outbreak to date began in Uganda in 2000, involving 425 presumptive cases and 224 deaths.

There are five distinct serotypes of Ebola virus, four of which have caused disease in humans: Ebola Zaïre, Ebola Sudan and Ebola Côte d’Ivoire. The fourth serotype, Ebola Reston, has caused severe illness in non-human primates but not in humans. Ebola Reston was first detected in October 1989 in Reston, Virginia (USA) in a colony of monkeys imported from the Philippines, and has subsequently caused outbreaks in non-human primates in Pennsylvania (Philadelphia), Texas (Alice) and Italy (Sienna). Several research workers became infected with the virus during these outbreaks, but did not become ill. Investigations traced the source of all outbreaks caused by the Reston strain to one export facility in the Philippines, but how the facility was contaminated has not been determined. The fifth serotype, Ebola Bundibugyo [ Towner et al, PLOS Pathogens ], was first identified as the cause of an outbreak in Uganda in 2007-8.

Figure: Timeline and outcome of Ebola haemorrhagic fever outbreaks, 1976-2009

* A: Democratic Republic of Congo, B: Sudan, C: Gabon, D: Uganda, E: Republic of Congo

 

Confirmed cases of Ebola haemorrhagic fever have been reported in the Democratic Republic of the Congo (formerly Zaire), Sudan, Gabon, Uganda, Republic of Congo and the Ivory Coast. Laboratory workers have been infected due to needle stick injuries in England, the USA and Russia.

A map of outbreaks is available.

Table: Outbreaks of Ebola haemorrhagic fever

Year	Country	Ebola virus subtype	Cases	Deaths	Case fatality rate
1976	Zaire (Democratic Republic of Congo)	Ebola-Zaire	318	280	88%
1976	Sudan	Ebola-Sudan	284	151	53%
1976	England	Ebola-Sudan	1	0	0%
1977	Zaire (DRC)	Ebola-Zaire	1	1	100%
1979	Sudan	Ebola-Sudan	34	22	65%
1989	USA	Ebola-Reston	0*	0	0%
1990	USA	Ebola-Reston	0*	0	0%
1992	Italy	Ebola-Reston	0*	0	0%
1994	Gabon	Ebola-Zaire	52	31	60%
1994	Côte d’Ivoire	Ebola-Côte d’Ivoire	1	0	0%
1995	Liberia	Ebola-Côte d’Ivoire	1	0	0%
1995	Democratic Republic of Congo (formerly Zaire)	Ebola-Zaire	315	250	79%
1996	Gabon	Ebola-Zaire	37	21	57%
1996	Gabon	Ebola-Zaire	60	45	75%
1996	South Africa	Ebola-Zaire	1	1	100%
2000-1	Uganda	Ebola-Sudan	425	224	53%
2001-2	Gabon and Republic of Congo	Ebola-Zaire	124	97	78%
2002-3	Republic of Congo	Ebola-Zaire	143	128	89%
2003	Republic of Congo	Ebola-Zaire	35	29	83%
2004	Sudan	Ebola-Sudan	17	7	41%
2005	Republic of Congo	n/k	12	9	75%
2007	Democratic Republic of Congo (formerly Zaire)	?Ebola-Zaire**	372	166	45%
2007	Uganda	Ebola-Bundibugyo	149†	37†	25%†
2008-9	D R Congo	n/k	32	15	47%
Total			2339	1492	64%

* Ebola-Reston was introduced into quarantine facilities by monkeys imported from the Philippines. A total of 8 humans developed antibodies but did not become ill

** Zaire type highly likely, but never confirmed

† Provisional figures

Natural Reservoir

Ebola virus is believed to be zoonotic, however the natural reservoir is unknown, despite extensive investigations. Non-human primates have been a source of human infection however they are not thought to be the reservoir as they develop severe, fatal illness when infected. High numbers of animal carcasses were noted in the surrounding areas prior to outbreaks in Gabon and the DRC, and recovered carcasses were infected with a variety of strains of Ebola virus suggesting they were not the reservoir but had been infected by more than one source.It is currently believed that humans and non-human primates are likely to be infected directly from the same natural reservoir species, or through a chain of transmission from this species.

Transmission

It is unknown how Ebola virus first passes to humans, however it is thought that the first case in an outbreak becomes infected through contact with an infected animal. The virus is then transmitted to others through direct contact with the blood, secretions, organs or other bodily fluids of infected persons. People can also become infected through contact with objects, such as needles or soiled clothing, that have been contaminated with infected secretions. Hospital workers have frequently been infected in Ebola outbreaks through close contact with infected patients, and insufficient use of correct infection control precautions and barrier nursing procedures. Outbreaks have also been fuelled by traditional burial practices, in which mourners have direct contact with the bodies of the deceased.

Humans may also be infected if they handle infected animals, or come into contact with their bodily fluids or cell cultures, and cases have been documented in people who handled infected chimpanzees, gorillas and forest antelopes, both dead and alive, in Cote d’Ivoire, the Republic of Congo and Gabon.

Symptoms

The incubation period of Ebola virus ranges from 2 to 21 days. The onset of illness is sudden, with fever, headache, joint and muscle pain, sore throat and intense weakness. This is then followed by diarrhoea, vomiting, rash, impaired kidney and liver function and stomach pain. Some patients may develop a rash, red eyes, hiccups, internal and external bleeding. Ebola haemorrhagic fever is fatal in between 50-90% of all clinically ill cases.

Diagnosis

Clinical diagnosis of Ebola virus in the early stages of infection is difficult, as early symptoms are non-specific and similar to those of many other diseases. However once later symptoms develop a clinical diagnosis of Ebola may be made. Laboratory findings show low counts of white blood cells and platelets, and elevated liver enzymes.

Laboratory diagnosis must be carried out under maximum biological containment conditions.  Tests are available to detect antibodies to the virus or viral DNA, and the virus may also be isolated in cell culture. People may also be tested for antibodies after recovery. New tests have been developed to test for the virus in samples of saliva and urine, and inactivated samples, to allow rapid laboratory diagnosis during outbreaks.

Treatment

There is no specific treatment or vaccine available for Ebola haemorrhagic fever, however potential new vaccines and drug therapies are being developed and tested. Patients require intensive supportive therapy including intravenous fluids or oral rehydration with solutions including electrolytes, maintaining their oxygen status and blood pressure.

Prevention

To avoid person to person transmission of Ebola virus, great care needs to be taken when nursing patients, to avoid contact with infected bodily fluids. Patients should be isolated, and strict barrier nursing techniques should be used, including wearing masks, gloves and gowns. Invasive procedures such as the placing of intravenous lines, handling of blood, secretions, catheters and suction devices are a particular risk and infection control is essential. Hospital staff should have their own individual gowns, gloves, masks and goggles. Non-disposable protective equipment must be properly disinfected before re-use. Other infection control measures include proper use, disinfection, and disposal of instruments and equipment used in caring for patients. Those that have died of Ebola virus infection should be promptly and safely buried.

UK Guidelines

In the UK, the procedures outlined in "The Management and Control of Viral Haemorrhagic Fevers"must be followed for any suspected case. The guidance is available here

 

Other guidelines and information are available:

• CDC Ebola virus information, including guidance for health professionals: ttp://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/ebola.htm
• http://www.cdc.gov/ncidod/dhqp/bp_vhf_interimGuidance.html
• WHO Infection Control for Viral Haemorrhagic Fevers in the African Healthcare setting: http://www.who.int/csr/resources/publications/ebola/whoemcesr982sec1-4.pdf