Ebola virus disease (EVD), previously known as Ebola haemorrhagenic fever, is a rare and serious illness in humans that is often fatal. The disease occurs in western and central Africa and is transmitted to humans via wild animals such as fruit bats and monkeys. It can also be spread between humans through direct contact with blood, secretions and organs.
Ebola virus disease is caused by viruses in the Orthoebolavirus family and there are various types that cause the disease. The most common is the Zaire strain but there are six distinct Ebola virus species in total, of which four (Zaire, Sudan, Bundibugyo, and Taï Forest) cause severe disease in humans, with fatality rates varying from 30 per cent to 90 per cent.
Two large-scale outbreaks in West Africa and the Democratic Republic of Congo have led to the development of vaccines and treatments.
Ebola symptoms can appear suddenly, typically between two and 21 days after infection. Early symptoms can be flu-like and include fever, extreme tiredness, headache, muscle pain, and sore throat.
Other symptoms include:
After recovering from Ebola, some people may have symptoms for two years or longer. These can include tiredness, headache, muscle and joint pain, eye pain and vision problems, loss of appetite, hair loss and skin problems, trouble sleeping, memory loss, hearing loss, depression, and anxiety. The virus can remain in bodily fluids such as semen for some time after a patient has recovered so there may be sexual transmission.
Ebola disease is often fatal, with a case fatality rate that has varied from 25-90 per cent in past outbreaks, but averages around 50 per cent.
The disease is highly contagious so precautions are needed for those caring for patients with the disease. In the largest ever outbreak – the 2013-16 west Africa epidemic – the World Health Organization estimated that health workers were between 21 and 32 times more likely to be affected by the disease than the general population.
Ebola is introduced into the human population through close contact with the blood, secretions, organs or other bodily fluids of infected animals such as fruit bats, monkeys, forest antelope or porcupines. Fruit bats of the Pteropodidae family are thought to be natural Ebola virus hosts.
Human-to-human transmission occurs via direct contact with the blood or body fluids of a person who is sick with or has died from Ebola. It can also spread by touching objects contaminated with body fluids (like blood, faeces, vomit) from an infected person or the body of a person who died from Ebola. The virus can enter the body through cuts in the skin or when touching one’s eyes, nose or mouth.
Burial ceremonies involving direct contact with the body of the deceased can also contribute to transmission.
Ebola is an emergency and needs to be treated quickly. Early medical care improves a person’s chances of surviving Ebola. Treatment involves supportive care, such as providing help with breathing, giving oral and intravenous fluids and administering medicines for pain and nausea. Patients will usually be treated in isolation in a hospital and will need specialist care in an intensive care unit.
In recent years treatments and vaccines have become available. In 2020 the US Food and drug administration approved two monoclonal antibodies (Inmazeb and Ebanga). They work by blocking the Ebola virus from entering the body’s cells.
Preventing Ebola involves avoiding contact with the body fluids of people and animals that are infected with the disease. This includes avoiding contact with blood, urine, faeces, saliva, sweat, vomit, breast milk, amniotic fluid, semen, and vaginal fluid from people who are sick.
Clothes, bedding, needles, medical equipment, or other items that may have touched an infected person’s blood or body fluids could also harbour the virus. In parts of Africa where the disease is prevalent washing a body before burial is an important ritual but this must be avoided if the patient has died from the disease.
It is also important to avoid contact with bats, forest antelopes, primates, and blood, fluids, or eat meat from these animals.
Two vaccines are licenced for the disease, but they cover the Zaire strain only. When someone is diagnosed with this type of Ebola a ring vaccination strategy is deployed – where the close contacts of the person infected are vaccinated to help prevent the spread.
Ebola first appeared in 1976 in two simultaneous outbreaks: in what is now South Sudan and in Zaire, now Democratic Republic of the Congo (DRC).. The latter occurred in a village near the Ebola river, from which the disease takes its name.
Until 2014 the disease was confined to rainforests in Central Africa, mainly in the Democratic Republic of the Congo, Sudan and Uganda. However, in 2013 there was an outbreak in the west African country of Guinea which then spread to Liberia and Sierra Leone, resulting in more than 28,000 cases, including 11,000 deaths. The slow regional, national and global response to the disease in the early stages, compounded by the three countries’ weak health systems, fuelled the spread of the virus.
DRC has been particularly affected by the disease and between 2018 and 2020 there was an outbreak in the North Kivu region that killed more than 2,287 people. These two outbreaks led to the development of treatments and vaccines.
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