Fruit bats are thought to be the natural hosts of the Ebola virus. Although the virus is no longer harmful for them, it is pathogenic in other wild animals from tropical rainforests, such as monkeys. Humans can be contaminated when handling these animals (butchering bushmeat, etc.). The virus then spreads among populations by human-to-human transmission.
In humans, the Ebola virus can be transmitted through direct contact with the blood or bodily fluids of sufferers, or through indirect contact with environments that have been contaminated by these fluids. The virus is not contagious during the incubation period. There is a moderate risk of infection in the first few hours after the initial symptoms appear, and a high risk once the disease has taken hold. Patients who have recovered from the disease are no longer infectious, but men can continue to spread the virus through their semen up to several months after clinical recovery.
Epidemics are caused by secondary human-to-human transmission. They can be exacerbated if people caring for Ebola virus patients do not take sufficient precautions. Funerals and burial ceremonies in which friends and relatives come into direct contact with the bodies of the deceased also strongly increase the risk of spreading the virus.
The only way to curb epidemics and human-to-human transmission is to take appropriate precautions to avoid infection, including regular hand-washing, isolating patients and not allowing skin or mucosa to come into contact with infected fluids. Physical protection, such as gloves, masks, goggles, gowns and boots, is vital. In recent years, an experimental vaccine has also been used in ring vaccination to stop the transmission of the virus.
The Ebola virus disease is a severe viral illness. Early signs resemble flu-like symptoms and are hard to diagnose – they include the sudden onset of fever over 38°C, weakness, muscle pain, headache and sore throat. These symptoms are followed by vomiting, diarrhea, rash, impaired kidney and liver function and in some cases internal and external bleeding. The incubation period, in other words the time between infection and the first symptoms, varies from 2 to 21 days, but is usually between 5 and 12 days.
Laboratory testing is the only way of confirming the diagnosis. Samples are tested under the strictest possible containment conditions.
The Ebola virus was first observed in 1976, with two simultaneous outbreaks in Sudan (151 deaths) and the Democratic Republic of the Congo (280 deaths). It was named "Ebola" after a river that flows through the DR Congo.
The Ebola virus belongs to the family Filoviridae (filoviruses), which has five distinct species: Bundibugyo (BDBV), Zaire (EBOV), Reston (RESTV), Sudan (SUDV) and Taï Forest (TAFV). The Ebola Bundibugyo, Zaire and Sudan strains have caused around 20 outbreaks of the disease in Central Africa, in remote villages near forests. The main outbreaks were in:
- 1995: 254 deaths in the Democratic Republic of the Congo,
- 2000: 224 deaths in Uganda,
- 2003: 128 deaths in the Congo,
- 2007: 187 deaths in the Democratic Republic of the Congo.
Until the current outbreak, the virus had claimed 1,590 victims.
In March 2014, a new outbreak of Zaire ebolavirus was identified in Guinea's forest region, spreading to neighboring countries Liberia and Sierra Leone and reaching urban areas. The virus then spread by air travel to Nigeria and by road to Senegal. In June 2016, when the World Health Organization (WHO) announced the official end of the epidemic, the record is sad: at least 28,000 officially declared cases, including more than 11,000 deaths. This is the largest known outbreak to date.
Sufferers of Ebola virus disease need intensive care to treat the symptoms (fever, pain and dehydration). There is currently no treatment for the disease and no vaccines have yet been approved by health authorities.
Ebola 2013-2016: lessons learned and how to respond to new epidemics
At the Institut Pasteur
The Institut Pasteur and the Institut Pasteur International Network are assisting the international aid effort by offering diagnostic support and epidemiological surveillance.
The National Reference Center for Viral Hemorrhagic Fevers, Lyon
The Jean Mérieux-Inserm BSL-4 laboratory in Lyon has been closely involved since the start of the outbreak. The laboratory houses the French National Reference Center (CNR) for Viral Hemorrhagic Fevers, which operates under the Institut Pasteur's Biology of Viral Emerging Infections Unit, directed by Sylvain Baize.
This team analyzed the first samples from Guinea during the 2013-2016 epidemic in West Africa and made the first positive diagnosis. Scientists also analyzed blood samples from patients and carried out tests to establish a detailed profile of the virus.
This team is on the front line of the fight against the Ebola virus. As well as analyzing samples in Lyon and monitoring suspected cases in France, in November 2014 it has has set up and directed the activity of the Macenta diagnostic center, in order to ensure the screening of patients during the epidemic of the time. Teams of volunteer scientists took turns in the field, who came not only from the Lyon unit of Sylvain Baize, but also from many teams at the Institut Pasteur in Paris, including the biological cell for emergency intervention.
In France, the National Reference Center for Viral Hemorrhagic Fevers, hosted by the Biology of Viral Emerging Infections Unit at the Institut Pasteur in Lyon, directed by Sylvain Baize, has been designated by the French Ministry of Health and tasked with contributing to diagnosis and epidemiological surveillance efforts for viral hemorrhagic fevers, in close collaboration with the French National Institute for Health Monitoring (InVS).
The Laboratory for Urgent Response to Biological Threats (CIBU)
In response to the Ebola epidemic that has been raging in West Africa since early 2014, the CIBU, directed by Jean-Claude Manuguerra, has been involved in work to diagnose samples from Guinea, in collaboration with the CNR team in Lyon. The CIBU has also been training volunteer scientists who are then sent to the diagnostic center in Macenta to help with diagnosis.
- Research projects at the Institut Pasteur in Paris
Improving our understanding of the Ebola virus
In order to develop better treatment strategies, design effective vaccines against Ebola and ensure continued efficacy of diagnostic tools, the evolution of the virus needs to be closely monitored. Then, with this in mind, a consortium of teams coordinated by the Institut Pasteur Ebola task force conducted analyses on samples from infected patients in different regions of Guinea during the 2013-2016 epidemic.thanks to the diagnostic work carried out by the Institut Pasteur in Dakar.
This sequencing work helped the scientists retrace the geographic spread of the virus and its progression over time. Epidemiological studies retracing the chains of transmission in Guinea have also been supplemented by data collected on the genetic variations of the virus. Finally, this data is critical for improving epidemic response strategies.
During this period, the team working under Amadou Sall (Institut Pasteur in Dakar) and Simon Cauchemez (Mathematical Modeling of Infectious Diseases Unit, Institut Pasteur in Paris) successfully reconstructed the chains of transmission of the Ebola virus and their context. They achieved this by conducting surveys on people living in Guinea's capital from February to August 2014. This data revealed the positive impact that control measures have had on the progression of the epidemic while highlighting the challenges that still need to be overcome to contain this epidemic in large urban centers. (The Lancet Infectious Diseases, January 23, 2015)
At the beginning of the 2013-2016 epidemic, the standard process used to diagnose Ebola took two to three days by RT-PCR and required sophisticated equipment and highly qualified medical workers. Moreover, the virus could only be detected once patients start showing symptoms, which can be mistaken for those of other infectious diseases raging in the region. Reducing the time and risks involved in the current diagnostic procedure wasa vital step in improving treatment for patients and increasing their chances of recovery.
At the Institut Pasteur, several research programs have been set up for the development of rapid diagnostic tests that are affordable and easy to use in the field or in hospitals. Pierre Lafaye, Head of the Antibody Engineering Platform, is coordinating these projects. One of these projects is a field diagnostic test which uses the RT LAMP enzyme to amplify DNA by reverse transcription at a stable temperature of roughly 60°C. The process is very fast (5 to 15 minutes) and highly sensitive. It was tested in December 2014 and compared to the standard test. Results showed that it was more sensitive than the standard test while having the same specificity. This test could detect the virus at earlier stages of infection and follow its progression in patients over a longer period of time.
The aim of this project is also to create a single, fast (using microfluidics), ultra-portable (paper-based) test to detect four diseases: dengue, malaria, Ebola and sleeping sickness.
Another project for a diagnostic test is designed for use in hospitals; it will require the involvement from health workers. It is highly sensitive and will be able to detect the presence of the virus in samples even before the first symptoms occur.
A scalable treatment to reach as many people as possible
The team led by Pierre Charneau (Molecular Virology and Vaccinology Unit) is working on development of a therapeutic Ebola vaccine. The advantage of a vaccine of this kind is that it can be used both to prevent infection and also as post-exposure treatment in the same way as regular medication. It could be administered to medical personnel with high exposure to the disease as well as patient contacts (family, friends) that could potentially be infected.
The technology used for this vaccine is based on non-integrative lentiviral vectors. These gene transfer vectors are unique in their ability to reliably introduce antigenic DNA into dendritic cells (i.e. cells that initiate the immune response). Scientists at the Institut Pasteur have composed an antigen using several small segments of the Ebola virus genome to make sure that the vaccine candidate is capable of inducing an intense cellular immune response that is fast and effective against all possible strains of the Ebola virus, on the basis of a single injection. Previous developments using the same technology against AIDS or malaria, have shown that these vaccines are effective in animals in very low doses, allowing for low production costs and therefore treatment which is accessible to the largest number of people possible. In the near future, the development of a vaccine would help to quell new epidemic foci by vaccinating those in close contact with new cases.
This vaccine will be developed and optimized for tests in animal models over the next few months in partnership with the Institut Pasteur in Dakar and the Institut Pasteur in Madagascar with field clinical trials to follow.
The Institut Pasteur teams working on the Ebola virus
National Reference Center for Viral Hemorrhagic Fevers, led by Sylvain Baize
Laboratory for Urgent Response to Biological Threats, led by Jean-Claude Manuguerra
Viral genomics and vaccination Unit, led by Frédéric Tangy
Molecular virology and vaccinology Unit, led by Pierre Charneau
Functionnal genetics of infectious diseases Unit, led by Anavaj Sakuntabhai
Institut Pasteur de Dakar, led by Amadou Sall