What is Ebola? Ebola virus disease

The Ebola outbreak in West Africa is the deadliest occurrence of the disease since its discovery in 1976.

Key facts

Ebola virus disease (EVD), formerly known as Ebola haemorrhagic fever, is a severe, often fatal illness in humans.
The virus is transmitted to people from wild animals and spreads in the human population through human-to-human transmission.
The average EVD case fatality rate is around 50%. Case fatality rates have varied from 25% to 90% in past outbreaks.
The first EVD outbreaks occurred in remote villages in Central Africa, near tropical rainforests, but the most recent outbreak in west Africa has involved major urban as well as rural areas.
Community engagement is key to successfully controlling outbreaks. Good outbreak control relies on applying a package of interventions, namely case management, surveillance and contact tracing, a good laboratory service, safe burials and social mobilisation.
Early supportive care with rehydration, symptomatic treatment improves survival. There is as yet no licensed treatment proven to neutralise the virus but a range of blood, immunological and drug therapies are under development.
There are currently no licensed Ebola vaccines but 2 potential candidates are undergoing evaluation.

Background

The Ebola virus causes an acute, serious illness which is often fatal if untreated. Ebola virus disease (EVD) first appeared in 1976 in 2 simultaneous outbreaks, one in Nzara, Sudan, and the other in Yambuku, Democratic Republic of Congo. The latter occurred in a village near the Ebola River, from which the disease takes its name.

The current outbreak in west Africa, (first cases notified in March 2014), is the largest and most complex Ebola outbreak since the Ebola virus was first discovered in 1976. There have been more cases and deaths in this outbreak than all others combined. It has also spread between countries starting in Guinea then spreading across land borders to Sierra Leone and Liberia, by air (1 traveller only) to Nigeria, and by land (1 traveller) to Senegal.

The most severely affected countries, Guinea, Sierra Leone and Liberia have very weak health systems, lacking human and infrastructural resources, having only recently emerged from long periods of conflict and instability. On August 8, the WHO Director-General declared this outbreak a Public Health Emergency of International Concern.

A separate, unrelated Ebola outbreak began in Boende, Equateur, an isolated part of the Democratic Republic of Congo.

The virus family Filoviridae includes 3 genera: Cuevavirus, Marburgvirus, and Ebolavirus. There are 5 species that have been identified: Zaire, Bundibugyo, Sudan, Reston and Taï Forest. The first 3, Bundibugyo ebolavirus, Zaire ebolavirus, and Sudan ebolavirus have been associated with large outbreaks in Africa. The virus causing the 2014 west African outbreak belongs to the Zaire species.

Transmission

It is thought that fruit bats of the Pteropodidae family are natural Ebola virus hosts. Ebola is introduced into the human population through close contact with the blood, secretions, organs or other bodily fluids of infected animals such as chimpanzees, gorillas, fruit bats, monkeys, forest antelope and porcupines found ill or dead or in the rainforest.

Ebola then spreads through human-to-human transmission via direct contact (through broken skin or mucous membranes) with the blood, secretions, organs or other bodily fluids of infected people, and with surfaces and materials (e.g. bedding, clothing) contaminated with these fluids.

Health-care workers have frequently been infected while treating patients with suspected or confirmed EVD. This has occurred through close contact with patients when infection control precautions are not strictly practiced.

Burial ceremonies in which mourners have direct contact with the body of the deceased person can also play a role in the transmission of Ebola.

People remain infectious as long as their blood and body fluids, including semen and breast milk, contain the virus. Men who have recovered from the disease can still transmit the virus through their semen for up to 7 weeks after recovery from illness.

Symptoms of Ebola virus disease

The incubation period, that is, the time interval from infection with the virus to onset of symptoms is 2 to 21 days. Humans are not infectious until they develop symptoms. First symptoms are the sudden onset of fever fatigue, muscle pain, headache and sore throat. This is followed by vomiting, diarrhoea, rash, symptoms of impaired kidney and liver function, and in some cases, both internal and external bleeding (e.g. oozing from the gums, blood in the stools). Laboratory findings include low white blood cell and platelet counts and elevated liver enzymes.

Diagnosis

It can be difficult to distinguish EVD from other infectious diseases such as malaria, typhoid fever and meningitis. Confirmation that symptoms are caused by Ebola virus infection are made using the following investigations:

antibody-capture enzyme-linked immunosorbent assay (ELISA)
antigen-capture detection tests
serum neutralization test
reverse transcriptase polymerase chain reaction (RT-PCR) assay
electron microscopy
virus isolation by cell culture.

Samples from patients are an extreme biohazard risk; laboratory testing on non-inactivated samples should be conducted under maximum biological containment conditions.

Treatment and vaccines

Supportive care-rehydration with oral or intravenous fluids- and treatment of specific symptoms, improves survival. There is as yet no proven treatment available for EVD. However, a range of potential treatments including blood products, immune therapies and drug therapies are currently being evaluated. No licensed vaccines are available yet, but 2 potential vaccines are undergoing human safety testing.

Prevention and control

Good outbreak control relies on applying a package of interventions, namely case management, surveillance and contact tracing, a good laboratory service, safe burials and social mobilisation. Community engagement is key to successfully controlling outbreaks. Raising awareness of risk factors for Ebola infection and protective measures that individuals can take is an effective way to reduce human transmission. Risk reduction messaging should focus on several factors:

Reducing the risk of wildlife-to-human transmission from contact with infected fruit bats or monkeys/apes and the consumption of their raw meat. Animals should be handled with gloves and other appropriate protective clothing. Animal products (blood and meat) should be thoroughly cooked before consumption.
Reducing the risk of human-to-human transmission from direct or close contact with people with Ebola symptoms, particularly with their bodily fluids. Gloves and appropriate personal protective equipment should be worn when taking care of ill patients at home. Regular hand washing is required after visiting patients in hospital, as well as after taking care of patients at home.
Outbreak containment measures including prompt and safe burial of the dead, identifying people who may have been in contact with someone infected with Ebola, monitoring the health of contacts for 21 days, the importance of separating the healthy from the sick to prevent further spread, the importance of good hygiene and maintaining a clean environment.

Controlling infection in health-care settings:

Health-care workers should always take standard precautions when caring for patients, regardless of their presumed diagnosis. These include basic hand hygiene, respiratory hygiene, use of personal protective equipment (to block splashes or other contact with infected materials), safe injection practices and safe burial practices.

Health-care workers caring for patients with suspected or confirmed Ebola virus should apply extra infection control measures to prevent contact with the patient’s blood and body fluids and contaminated surfaces or materials such as clothing and bedding. When in close contact (within 1 metre) of patients with EBV, health-care workers should wear face protection (a face shield or a medical mask and goggles), a clean, non-sterile long-sleeved gown, and gloves (sterile gloves for some procedures).

Laboratory workers are also at risk. Samples taken from humans and animals for investigation of Ebola infection should be handled by trained staff and processed in suitably equipped laboratories.

WHO response

WHO aims to prevent Ebola outbreaks by maintaining surveillance for Ebola virus disease and supporting at-risk countries to developed preparedness plans. The document provides overall guidance for control of Ebola and Marburg virus outbreaks:

Ebola and Marburg virus disease epidemics: preparedness, alert, control, and evaluation

When an outbreak is detected WHO responds by supporting surveillance, community engagement, case management, laboratory services, contact tracing, infection control, logistical support and training and assistance with safe burial practices.

Q: What is Ebola?

A: Ebola virus disease (EVD) is described by the World Health Organisation (WHO) as "a severe, often fatal illness in humans." It first appeared in 1976 in two simultaneous outbreaks – in Nzara, Sudan; and in Yambuku, in the Democratic Republic of Congo. The latter was in a village situated near the Ebola River, from which the disease takes its name.

The disease is mainly found in tropical Central and West Africa, and can have a 90 per cent mortality rate. In the current outbreak the death rates are running at about 70 per cent.

Q: How bad is the current outbreak?

A: The WHO and other international government agencies have reported a total of 4,493 deaths and 8,998 suspected cases of the disease. However the WHO believes that this substantially understates the magnitude of the outbreak, with possibly 2.5 times as many cases as have been reported Although this the largest outbreak ever recorded of the disease there have been significant sporadic outbreaks in the past, mainly in Uganda, the DRC, Sudan and Gabon. The worst previous outbreak, in 2000 in Uganda, saw 425 people infected. Just over half died.

The current epidemic began in Guinea when a 2-year-old boy called Emile died on 6 December last year in the village of Meliandou, Guéckédou Prefecture. His mother, sister, and grandmother then became ill with similar symptoms and also died. People infected by those victims spread the disease to other villages, eventually crossing into neighbouring Liberia and Sierra Leone.

Q: How is the virus transmitted?

A: The virus is known to live in fruit bats, and normally affects people living in or near tropical rainforests. It is introduced into the human population through close contact with the sweat, blood, secretions, organs or other bodily fluids of infected animals such as fruit bats, chimpanzees, forest antelope and porcupines found ill or dead or in the rainforest.

The virus spreads among populations through human-to-human transmission, with infection resulting from direct contact, through broken skin or mucous membranes, and indirect contact with environments or objects contaminated with such fluids, such as door handles and telephones.

Q: What does Ebola do?

A: Symptoms begin with fever, muscle pain and a sore throat, escalating rapidly to vomiting, diarrhoea and internal and external bleeding, leading quickly to death. Health workers are at serious risk of contracting the disease and need to wear a protective suit covering their entire body.

Q: Why is it spreading so rapidly in Liberia, Sierra Leone and Guinea?

A: Many of the areas that are seriously affected already suffer extreme poverty and have limited access to soap or running water to help control the spread of disease. Hospitals in these countries frequently lack basic supplies and are understaffed. Another significant problem is that burial ceremonies, in which mourners have direct contact with the body of the deceased person, can increase the spread of the disease.

Q How long does the virus survive?

A: One thing in mankind's favour is that the Ebola virus is quite fragile and easily destroyed by high temperatures, being dried out and disinfectants such as soapy water and alcohol gel.

It will survive a few days at longest if left in a pool of bodily fluid, such as spit or blood, in a cool, damp place.

Q: Is the disease treatable?

A: Early treatment improves a patient's chances of survival. However there is no vaccine or cure. Severely ill patients require intensive supportive. Patients are frequently dehydrated and require oral rehydration with solutions containing electrolytes or intravenous fluids.

There are limited supplies of experimental drugs, including ZMapp, a combination of monoclonal antibodies.

Q: Is there a vaccine?

A: An experimental vaccine, known as the cAd 3-ZEBOV, began Phase 1 trials on volunteers in Oxford and Bethesda last month. The vaccine is being administered to a further group of volunteers in Mali this month. If successful, the vaccine will be fast tracked for use in West Africa. A second vaccine, rVSV-ZEBOV, developed by the Public Health Agency of Canada, is ready to undergo Phase 1 trials.

Q: When did Ebola reach Britain?

A: The Government launched screening of passengers arriving at Heathrow and Gatwick airports and the Eurostar terminal at St Pancras.

On December 29 a health care worker who was helping combat the disease in Sierra Leone was diagnosed with the disease and was being treated in a Glasgow hospital.

Q: Can Ebola be stopped?

A The United Nations says it believes the world can defeat the Ebola outbreak in West Africa in six to nine months, “but only if a 'massive’ global response is implemented.”

UN secretary-general Ban Ki-moon has criticised the international response, saying that a trust fund he launched to fight Ebola has only raised $100,000 of its $1 billion target.

As part of its effort British army medics are on their way to West Africa to help in the fight against the virus. A team of 91 medics from 22 Field Hospital in Aldershot will run a hospital in Sierra Leone, set aside for health care workers who risk infection. The nurses, doctors and infectious disease consultants will join 40 soldiers already there.