Ebola virus, of which there are five species, is a Filovirus, closely related to the Marburg virus. It was first described in two outbreaks in 1976 in Sudan and the Democratic Republic of Congo. Its natural host is thought to be the fruit bat, though it infects a variety of other animals, including chimpanzees, monkeys, gorillas and antelopes.
Since the first known occurrence of human Ebola virus infection in 1976, there have been 24 outbreaks in Central and West Africa1 prior to the current outbreak. One species of the virus, found in China and the Philippines, is also capable of infecting humans, but to date no human cases of illness or death have been reported.
The virus is transmitted to humans only by contact with blood or other body fluids of infected animals, and from human to human only by contact with blood or body fluids of infected persons. There is no other mode of human to human transmission. For this reason, those most at risk of infection are healthcare professionals caring for patients infected with Ebola virus, family members and close friends of infected individuals in close contact with or caring for them, and those involved in funeral ceremonies or disposal of the bodies of infected individuals. The virus is found in the semen of infected males, so sexual transmission is possible.
The likely source of animal to human transmission is the handling of infected animal carcasses, in particular during the trade in bush meat.
After an incubation period of two to 21 days, the onset is characterised by fever, muscle pains and severe weakness, headache, sore throat and rash. There follows a GI phase, with diarrhoea, vomiting and abdominal pain. The liver, pancreas and kidneys may become involved at this stage, with impairment of hepatic and/or renal function. Finally, the patient enters a state of shock with hypovolaemia, tachycardia and haemorrhagic features. The case fatality rate may be as high as 90%. Ebola virus may continue to be present in body fluids for up to seven weeks or more, and as long as the virus is present in body fluids, the individual is still infectious.
The most important factor initially is a high level of suspicion when confronted with a feverish, ill patient who has potentially been exposed to infection. A careful history is essential, including a precise itinerary in the case of travellers returning home ill or becoming ill after their return, having regard to the incubation period of Ebola virus infection, and a history of contact with any individuals who were ill or subsequently became ill.
Routine blood tests show reduced white cell and platelet counts and abnormal LFTs. The virus itself may be identified by electron microscopy or cell culture and a range of serological tests can be employed to detect its presence.
There is currently no definitive treatment for Ebola virus infection. Treatment is entirely supportive, including fluid and electrolyte replacement. Two infected US aid workers have been given an experimental treatment, known as ZmappTM,2 a mixture of three monoclonal antibodies against the Ebola virus with ‘apparently encouraging’ signs in one of them. Another experimental drug is designed to target virus RNA.
Prevention and control
There is currently no vaccine available against Ebola virus, but the director of the US National Institute of Allergy and Infectious Diseases3 has said that clinical trials will start in September on a vaccine that has shown promising results during tests on animals. Several other vaccines are also in the process of evaluation. Canada has announced it will donate up to 1,000 doses of an experimental Ebola vaccine to help fight the outbreak.
Reducing the risk of animal to human transmission can be achieved if bush meat is avoided or not consumed raw, if gloves are worn while handling animal carcasses and if all meat is thoroughly cooked. These precautions should also apply to those slaughtering or handling the carcasses of farm animals or sick animals, especially pigs, which can be infected with one of the species of Ebola virus. Meat from these animals must be thoroughly cooked before being eaten.
Reducing human to human transmission is more complicated. Known cases of Ebola virus infection should, as far as possible, be isolated in hospital. If this is not socially or culturally acceptable, close physical contact should be avoided and gloves and protective clothing should be worn by those caring for these patients. Hand hygiene must be scrupulously observed by carers and visitors. Similar precautions must be observed when disposing of the bodies of those who have died from the infection.
Healthcare workers in hospital in contact with patients infected with, or suspected of being infected with, Ebola virus must wear gloves, masks and protective clothing, including goggles, to protect them from accidental contact with blood or other body fluids. They must also adopt safe injection practices and safe disposal of sharps and other material in contact with infected patients, and must take care to avoid needlestick injuries. Laboratory workers handling specimens from actual or potential Ebola-infected patients must be specially trained to handle infected material safely.
The outbreak in West Africa
The current outbreak of Ebola virus began in Guinea in March 2014 and has spread to Liberia, Nigeria and Sierra Leone. According to the WHO4, by 6 August, the total of cases in the four countries had reached 1,779 with 961 deaths.
On 6 and 7 August, an emergency committee designated this outbreak a public health emergency of international concern. The committee advised that ‘the Ebola outbreak in West Africa constitutes an 'extraordinary event' and a public health risk to other states; that the possible consequences of further international spread are particularly serious in view of the virulence of the virus, the intensive community and health facility transmission patterns, and the weak health systems in the currently affected and most at-risk countries; and that a co-ordinated international response is deemed essential to stop and reverse the international spread of Ebola’.
By 13 August, the number of deaths had risen to 1,013 and the WHO declared Kenya at high risk from the outbreak, because of its position as a travel hub for West African countries.5
In the UK, the risk is said to be very low and the Foreign and Commonwealth Office is not currently advising a ban on travel to the countries concerned,6 although it would appear wise not to travel there unless absolutely necessary. Anyone who finds it necessary to travel to Guinea, Liberia, Nigeria or Sierra Leone should be advised to follow all of the precautions outlined above to avoid infection via animal carcasses or meat and via human to human transmission.
- Ebola virus disease is a severe and frequently fatal illness in humans, with a case fatality rate of up to 90%
- It occurs mainly in rural areas of Central and West Africa
- The virus is initially transmitted to people from animals and spreads by human to human transmission through contact with blood and other body fluids
- There is currently no treatment and no preventive vaccine
- The risk of Ebola virus infection in the UK is low
1. World Health Organisation. www.who.int/mediacentre/factsheets/fs103/en/
2. Mapp Biopharmaceutical Inc. www.mappbio.com/zmapinfo.pdf
3. BBC News. www.bbc.co.uk/news/health-28656079
5. BBC News. www.bbc.co.uk/news/world-africa-28769678
6. Foreign & Commonwealth Office. www.gov.uk/government/news/ebola-government-response
- Dr Townend is chairman of the British Global and Travel Health Association (www.bgtha.org)