How Did the Ebola Virus Change Epidemiology?

SadaNews - The Ebola virus is no longer just a name associated with the fear of bleeding and rapid death, but has become one of the most important models through which the world has tested its ability to confront high-risk epidemics.

Since its first appearance in 1976, this virus has revealed with each new outbreak that the battle against infectious diseases is not determined solely by laboratories or hospitals, but by a delicate balance between science, early surveillance, community trust, and the strength of health systems.

Ebola belongs to the family of filoviruses, which appear under the microscope as long, twisted threads. The disease causes severe hemorrhagic fever that can quickly progress to organ failure and internal or external bleeding, especially if diagnosis is delayed or if the patient does not receive intensive supportive care in a timely manner.

The World Health Organization indicates that the historical average mortality rate for Ebola is around 50%, but it has varied significantly from one outbreak to another, ranging from 25% to 90%, depending on the virus type, speed of intervention, quality of medical care, and the ability of health authorities to isolate cases and trace contacts.

A Virus that Changed the World's Understanding of Epidemics

Ebola first appeared in 1976 during two nearly simultaneous outbreaks; one in Nzara, known today as South Sudan, and the other in Yambuku in the current Democratic Republic of the Congo near the Ebola River, from which the disease took its name.

Since then, Ebola is no longer an isolated disease in a specific region, but has become a clear example of how a virus that spreads in a remote village can turn into a regional and perhaps global threat if it coincides with weak surveillance, delayed diagnosis, and a lack of trust between the population and health teams.

The West Africa outbreak from 2014 to 2016 represented a major turning point in the history of the disease. It infected more than 28,000 people and caused the deaths of over 11,000, primarily spreading in Guinea, Liberia, and Sierra Leone, with subsequent cases reported in other countries linked to travel or secondary infection.

This outbreak was the largest in Ebola's history, revealing that the disease not only threatens individual lives but can shake entire health systems and impact the economy, education, movement, and public trust.

Multiple Types and Varying Risks

Ebola is not a single virus in a narrow sense, but a group of closely related species. Among the most important species associated with human infection are:

Zaire virus, which is most associated with major outbreaks and is the most dangerous, and against which the most important vaccines and treatments currently approved have been developed.

Sudan virus, first recorded in 1976, has a history of outbreaks in Uganda, Sudan, and South Sudan and continues to pose a challenge because vaccines and treatments approved against Zaire do not necessarily provide confirmed protection against it.

Bundibugyo virus, discovered in 2007, has been linked to fewer outbreaks compared to Zaire but remains capable of causing severe disease and deaths, especially in environments with fragile health systems or delayed containment.

These species differ in their genetic makeup, virulence levels, and associated mortality rates, as well as in their response to available vaccines and treatments. Thus, the medical question today is no longer: Do we have a vaccine against Ebola? But: Against which type of Ebola? In what epidemiological context? For which population group?

How is Ebola Transmitted?

The Ebola virus is primarily transmitted through direct contact with the blood or bodily fluids of an infected or deceased person. These fluids include vomit, feces, urine, saliva, sweat, blood, semen, and other bodily secretions.

Ebola does not spread in the same way that respiratory viruses like influenza or COVID-19 do; it typically does not transmit through the air or merely by passing by an infected person in a public place. The real risk begins with direct contact with the patient’s fluids, or touching contaminated items such as needles, clothing, or bed linens, or unsafe handling of deceased bodies during funeral practices.

Transmission from animals to humans may initiate some outbreaks, especially when dealing with infected or dead wild animals such as bats, certain primates, and antelopes. After the virus enters the community, its transmission from human to human becomes the critical factor in the scale of the outbreak.

Ordinary Symptoms Turn Severe

The difficulty with Ebola lies in its initial symptoms, which may resemble many common diseases in Africa, such as malaria, typhoid, or influenza. Symptoms usually begin after an incubation period ranging from two to 21 days, often appearing within 8 to 10 days of exposure to the virus.

In the early stage, the infected person experiences sudden fever, severe fatigue, headache, muscle and joint pain, and sore throat. These symptoms may not seem sufficient to raise suspicion, especially in areas where other febrile diseases are prevalent.

But as the illness progresses, more severe signs appear, such as vomiting, severe diarrhea, abdominal pain, rash, and acute dehydration. In advanced cases, bleeding may occur from the nose or gums, or bruising and bleeding under the skin may develop, or blood may be present in vomit or feces, alongside liver and kidney dysfunction, dropping blood pressure, and neurological disturbances such as confusion and irritability.

Here, the importance of early diagnosis becomes clear, as the patient in the initial days may benefit more from fluid and electrolyte replacement and directed treatment, whereas delays can lead the body into a downward spiral of dehydration, shock, and organ failure.

Confirmatory diagnosis of Ebola depends on the direct detection of the virus in blood, often using a polymerase chain reaction (PCR) test. This test is crucial because it distinguishes Ebola from other diseases that may share similar symptoms.

Accompanying analyses help estimate the severity of the case, such as low platelet counts, elevated liver enzymes, kidney dysfunction, and changes in inflammatory and coagulation markers. While these indicators alone are insufficient to confirm the disease, they provide doctors with a clearer picture of the case's trajectory and its risk of deterioration.

Medical guidelines emphasize isolating the suspected case immediately upon symptom onset, given a history of possible exposure, without waiting for the final result if suspicion is strong; any delay in isolation could allow the virus to spread within the household or healthcare facility.

From Supportive Care to Targeted Treatments

For a long time, the treatment of Ebola relied primarily on supportive care: fluid and electrolyte replacement, blood pressure stabilization, dehydration treatment, respiratory support if needed, monitoring of kidney and liver functions, and treating secondary bacterial infections if they arose.

This care is not a simple or secondary matter. Clinical experience has shown that providing sufficient fluids and salts and correcting body imbalances can significantly improve survival chances, especially if started early.

But a turning point came with the development of targeted treatments based on monoclonal antibodies. In the PALM trial conducted during the 2018-2019 Democratic Republic of the Congo outbreak, several experimental treatments were compared, and the results showed that some antibodies, such as REGN-EB3 and mAb114, were better than others at reducing mortality, especially when used early.

Subsequently, the U.S. Food and Drug Administration approved two treatments against the Zaire virus: Inmazeb, a combination of three antibodies, and Ebanga, a monoclonal antibody. In the data for Ebanga, for example, the 28-day mortality was 35.1% among those receiving treatment, compared to 49.4% in the control group, reflecting the importance of transitioning from supportive care alone to targeted therapy when the viral type is appropriate and the treatment is available.

Nevertheless, the picture should not be overstated; these treatments do not cover all types of Ebola and are not a substitute for isolation, surveillance, and infection control. They also require qualified centers, precise protocols, and supply chains capable of reaching outbreak areas.

Vaccines: The Greatest Achievement in Modern Ebola History

The development of an effective vaccine against Ebola is one of the most significant achievements in the history of fighting the virus. The rVSV-ZEBOV vaccine, commercially known as Ervebo, showed strong results in a ring vaccination trial conducted in Guinea during the West Africa outbreak. The concept of ring vaccination involves vaccinating contacts of confirmed cases and the contacts of those contacts, aiming to create a protective circle around the virus to prevent its spread within the community.

Trial data indicate that individuals who were vaccinated immediately within the vaccination rings did not experience any Ebola cases after a sufficient period for protection formation, making this vaccine a pivotal tool in the response to outbreaks associated with the Zaire virus.

In 2019, Ervebo received international regulatory recognition and became the first Ebola vaccine prequalified by the World Health Organization for use in high-risk countries. This vaccine is given in a single dose and is particularly useful in outbreak conditions when speed is a critical factor.

There is also another two-dose vaccination system known as Zabdeno and Mvabea, which relies on an initial dose followed by a second dose after about eight weeks. This regimen may be more suitable for proactive prevention in the most vulnerable groups, such as healthcare workers or residents of at-risk areas, but it is not the optimal choice for rapid response in the heart of an outbreak, as building protection takes longer.

The crucial point remains that the available vaccines are primarily focused against the Zaire virus, while the need persists for developing effective vaccines against the Sudan and Bundibugyo viruses and other types.

Why Does Control Sometimes Fail Despite Science?

Ebola experiences prove that the availability of a vaccine or treatment does not automatically equate to controlling an outbreak. The virus often prevails when several factors converge: delayed case detection, weak trust in health teams, lack of beds and protective equipment, difficulty accessing affected areas, armed conflicts, or continued unsafe burial practices.

In many outbreaks, the problem was not solely the absence of medical knowledge but the gap between that knowledge and the community. When people reject isolation, hide patients out of fear of stigma, or perceive response teams as a threat, transmission chains continue even if scientific tools are available.

Thus, community trust has become part of the treatment. Health education, engaging local and religious leaders, respecting the dignity of the deceased during safe burials, and communicating in an understandable language are all elements that are as crucial as gloves, masks, and vaccines.

Prevention Measures: A Comprehensive Package

International guidelines emphasize that controlling Ebola does not rely on a single procedure but on an integrated package that includes:

Rapid isolation of suspected and confirmed cases in designated places.

Daily tracking and monitoring of contacts throughout the incubation period, which can extend to 21 days.

Using personal protective equipment inside health facilities, especially when dealing with blood, vomit, feces, or any bodily fluids.

Disinfecting surfaces and medical instruments, and safe disposal of contaminated waste.

Safe and humane handling of deceased bodies, as the virus may remain present in bodily fluids post-mortem.

Community awareness of the real modes of transmission, to avoid panic on one hand, and prevent underestimation on the other.

Using approved vaccines in appropriate areas, especially in Zaire virus outbreaks.

Strengthening laboratories and epidemiological surveillance, enabling early case detection and preventing limited infections from escalating into widespread outbreaks.

Ebola in the Global Health Security Balance

Ebola has changed the way the world thinks about health security. It has shown that infectious diseases are no longer a local issue pertaining to a specific country, and that the weakness of a health system in a limited area can become a global test if intervention is delayed.

It has also proved that investing in scientific research is not a luxury but a strategic line of defense. The difference between past and present outbreaks lies not only in the availability of vaccines and treatments but in the world’s learning how to develop its tools during a crisis and how to conduct clinical trials in complex epidemic conditions without abandoning scientific and ethical standards.

Nevertheless, the battle remains open. The emergence of new outbreaks, the persistence of some viral types without an approved vaccine or treatment, and the intersection of epidemics with conflicts, migration, and poverty all contribute to making Ebola a persistent threat that does not belong solely to the past.

Source: Al Jazeera