Site author Richard Steane
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Ebola Virus Disease (EVD)

[Split off from a unit on common (human) diseases caused by infection by a virus]

I have produced this section in response to events in Africa.

Between 2014 and 2016, a total of 28,616 cases of EVD and 11,310 deaths were reported in Guinea, Liberia, and Sierra Leone. This has sustantially affected healthcare workers. Liberia lost 8% of its doctors, nurses, and midwives to the virus, and events adversely affected treatment and control of HIV, tuberculosis, measles, and malaria in these countries. A number of foreign healthcare workers (from the UK and USA and other parts of the world) and ordinary travellers have been exposed to or actually contracted the disease but most have recovered after returning to their home countries.

In January 2020 there were 3416 confirmed cases and 2237 deaths in the North Kivu and Ituri provinces of the Democratic Republic of the Congo, and this is the world's second largest Ebola epidemic on record. The WHO was optimistic about treating this outbreak but ethnic violence was directed towards healthcare workers and there are fears that 300,000 people have been displaced and this may spread the virus.
It was declared a Public Health Emergency of International Concern (PHEIC).

In June 2020 the WHO reported that new genetic sequence analysis by the Democratic Republic of the Congo's National Institute of Biomedical Research (INRB) has found that the newly-identified Ebola virus circulating in the Equateur Province in western Democratic Republic of the Congo is different from the one which has infected more than 3400 people in the eastern part of the country.

Disease - Ebola Virus Disease (EVD)

Caused by
Ebolavirus (EBOV) - named after the Ebola River in the Democratic Republic of the Congo (formerly known as Zaire), the location of the first known outbreak (in August 1976)
PHIL_1832_lores (42K)
Image courtesy CDC

The virus particle has an unusual shape.
Other similar viruses - possibly resulting from mutations - are known for their effects on humans or other primates (some first seen in biological laboratories).

Signs and Symptoms:
Ebola is a haemorrhagic fever, i.e. it causes high temperature and the escape of blood - internally or externally. Some symptoms may initially resemble influenza, "stomach bugs" or malaria, but they then develop into a more serious phase.

Symptoms of Ebola include
Symptoms may appear anywhere from 2 to 21 days after exposure (average 8-10 days).

It is thought that sufferers are infectious (i.e. can pass on the disease in body fluids) from the time symptoms appear, but these devlop gradually. The CDC says that Ebola is only contagious if the person is experiencing active symptoms.

In survivors, the virus may remain in parts of the body which are not subject to the protection of the immune system: the eyes, brain and spinal cord. It may be latent for some time, and in some cases cause meningitis (inflammation of the membranes surrounding the brain and spinal cord).

Similarly, it has been found that some male survivors produce virus particles in their semen for some time. Unprotected sex may therefore spread the virus.

The WHO states that the average EVD case fatality rate is around 50%. Case fatality rates have varied from 25% to 90% in past outbreaks.

Recovery from Ebola depends on good supportive clinical care and the patient's immune response.

Oral reydration therapy (dilute solution of sugar and salts, taken by mouth) or intravenous therapy (similar solution, from a 'drip') are helpful.

In a community context Ebola cases need to be identified, isolated and treated. Possible contacts need to be traced, and treated in order to break the chains of transmission. Health care workers must strictly follow infection control (barrier nursing) in hospitals [or substitute buildings]. Safe burial practices may differ from traditional methods. It is better to check travellers before (or during?) flight than on arrival.

Specific chemical treatments for Ebola have not undergone some of the usual testing procedures. It may be said that the development of these drugs are subject to different economic and scientific influences in Africa and the western world.

Several chemicals seen as candidates for treating Ebola have been fast-tracked. Their potential side-effects and the lack of randomised clinical trials have been sidelined in the light of the perceived risks of Ebola.

Certain anti-viral drugs approved for other viral infections have been used in the treatment of Ebola, mostly in Africa, but it is difficult to compare their effectiveness as conditions are not standardised.

One possibility was the experimental drug ZMapp which is based on a combination of three monoclonal antibodies, aimed specifically at Ebola proteins. There are, however, several practical problems with it, including need for refrigeration and multiple dosing. It was in rather short supply. Two other general antiviral drugs, favipiravir (a viral RNA-dependent RNA polymerase inhibitor) and GS-5734 - also known as remdesivir (a nucleotide analogue), have been seen as showing more potential.

Between November 2018 and August 2019, 681 people with confirmed Ebola infection were enrolled into a drugs trial.
Participants could be any age, and included infants and pregnant women. The researchers randomly assigned participants to receive one of four experimental drugs: ZMapp, Mab114, REGN-EB3, or remdesivir.
After results from the first stage of a trial using 499 participants had been reviewed, the safety monitors recommended that two drugs - ZMapp and remdesivir - be dropped from the remainder of the trial, as these two drugs were much less effective at preventing death. Since that time, remdesivir has been tried against COVID 19.

In 2014-6 there was no vaccine against Ebola, although some went through stages of testing in Africa, but this stalled because large numbers of volunteers were needed for the next stage of testing.
There are now several vaccines in various stages of testing against the Ebola virus, and specifically the 'Zaire' strain of it. There are other strains, and the 'Sudan' strain is the next most common, but the surface glycoproteins on the different strains differ considerably so vaccines may be less effective in other outbreaks.

The two main vaccines are mainly known by their manufacturer's names (although development work has been carried out by several groups of workers in different countries). Their codes include 'Z' which refer to the Zaire strain:
GSK produced a vaccine based on an attenuated chimpanzee adenovirus vector -cAd3-EBO Z
Merck Sharp & Dohme (MSD) produced one using attenuated vesicular stomatitis virus - rVSV-ZEBOV.

In January 2021 the four leading international health and humanitarian organizations UNICEF, WHO, IFRC and MSF announced the establishment of a global Ebola vaccine stockpile - 'injectable single-dose Ebola vaccine' (rVSVΔG-ZEBOV-GP, live) to ensure outbreak response. Evidently the vaccine had been administered to more than 350,000 people in Guinea and in the 2018-2020 Ebola outbreaks in the Democratic Republic of the Congo.

It has been shown that ring vaccination is a highly effective means of preventing spread of the disease. This involves vaccinating those infected with Ebola as well as all their contacts, and also contacts of contacts. A programme of vaccination of healthcare workers has been instituted in several countries, especially in border areas.

People who recover from Ebola infection develop antibodies that last for at least 10 years.

Spread by:
Mainly by direct contact of the outer surface of the human body: skin (possibly damaged), eyes, nose, or mouth (mucous membranes) with blood or body fluids (urine, saliva, sweat, faeces, vomit, breast milk, or semen) from an infected individual.
Everyday social practices - handshakes etc - can cause widening of its spread in epidemic situations.

Transfer can also take place in a hospital setting via hypodermic needles and scalpel blades ("sharps") - sometimes re-used in certain circumstances.

Outbreaks are thought to have originated from wild (African) animals such as fruit bats of the family Pteropodidae, porcupines and bushmeat - including monkeys.

* It is not spread via the air by droplet infection. *

The virus is deactivated by normal disinfectants but it may be easily spread by sloppiness in hygiene.

Full (disposable) protective clothing including face masks is required for healthcare and associated personnel including those disposing of bodies, and this may be a special problem in hot conditions (especially when being removed).

Other topics on this site

Common (human) diseases caused by infection by a virus Was an introduction to this topic - now moved to be an independent file.

HIV/AIDS Part of a topic on Cell recognition

Virus particles Contrasting viruses with cellular organisms

Ebola Web Links

2014-2016 Ebola Outbreak in West Africa CDC. Centers for Disease Control and Prevention. CDC 24/7: Saving Lives. Protecting People.

Ebola virus disease from the World Health Organisation

Ebola (Ebola Virus Disease) CDC update

Deadly Ebola outbreak 'not global threat'

Ebola virus disease From Wikipedia, the free encyclopedia

Ebola virus epidemic in West Africa

History in the making:

Ebola: The First Glimpse of a Virus


Ebola screening begins at Heathrow airport

BBC News Africa items:

Why Ebola is so dangerous

I caught Ebola in Guinea and survived

UNICEF, WHO, IFRC and MSF announce the establishment of a global Ebola vaccine stockpile

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