Ebola virus disease (EVD) is a serious and often deadly illness caused by viruses in the Ebolavirus group, which are part of the Filoviridae family. The virus is zoonotic, meaning it can spread from animals to humans. Fruit bats, particularly those in the Pteropodidae family, are believed to be the natural hosts of the virus. People can catch Ebola through direct contact with the blood, body fluids (such as saliva, sweat, urine, or vomit), organs, or tissues of an infected person. The virus can also spread by touching objects or surfaces contaminated with these fluids. Most human-to-human spread happens in places with poor infection control, such as under-resourced healthcare facilities, or during traditional burial practices that involve handling the body of someone who died from the disease.
After a person is infected, symptoms usually appear within 2 to 21 days. The illness often starts suddenly with fever, extreme weakness, muscle aches, headaches, and sore throat. This is followed by vomiting, diarrhoea, and problems with kidney and liver function. In some cases, both internal and external bleeding can occur. The risk of death varies depending on the outbreak, the type of Ebola virus, and the quality of medical care, but more than half of patients may die, with some outbreaks killing over 70% of those infected.
Ebola was first identified in 1976 during two outbreaks at the same time—one in Nzara, Sudan, and the other in Yambuku, in what is now the Democratic Republic of the Congo. The second outbreak occurred near the Ebola River, which gave the virus its name. Since then, several outbreaks have happened, mainly in Central and West Africa. The largest was between 2014 and 2016, when more than 28,000 cases and over 11,000 deaths were reported. Better medical care, new experimental treatments, and preventive measures such as the rVSV-ZEBOV vaccine have improved survival rates and reduced the risk of spread, but early detection, fast response, and ongoing prevention are still major challenges in areas where the disease is most common.
History of Outbreaks
Ebola virus disease (EVD) was first identified in 1976 during two simultaneous outbreaks: one in Nzara, Sudan (now South Sudan), and another in Yambuku, a village near the Ebola River in what is now the Democratic Republic of the Congo (DRC). The outbreaks were caused by two different species of the virus—Sudan ebolavirus and Zaire ebolavirus—and together resulted in hundreds of deaths. Since then, EVD has caused multiple outbreaks, most of them concentrated in Central and West Africa, where the virus’s natural reservoirs and human-wildlife interactions create conditions for sporadic spillover events.
The most devastating Ebola epidemic to date occurred between 2014 and 2016 in West Africa, affecting primarily Guinea, Liberia, and Sierra Leone. This outbreak resulted in more than 28,000 reported cases and over 11,000 deaths, making it the largest and deadliest in the history of the disease. Contributing factors included weak healthcare infrastructure, delayed recognition of the outbreak, and high population mobility across porous borders. Urban transmission—rare in earlier outbreaks—played a significant role in its spread. Other significant outbreaks include the 2018–2020 epidemic in eastern DRC, which recorded more than 3,400 cases and 2,200 deaths, complicated by ongoing armed conflict that hampered access to affected communities. Smaller outbreaks have also been documented in countries such as Uganda, Sudan, and Gabon, often linked to localized exposure events.
Virus Classification
The Ebola virus is a member of the Filoviridae family, which includes filamentous viruses. The genus Ebolavirus contains six known species:
| Species | Notable Characteristics |
| Zaire ebolavirus | Most deadly, responsible for major outbreaks |
| Sudan ebolavirus | Causes severe disease, less lethal than Zaire |
| Taï Forest ebolavirus | Rare, originally found in Ivory Coast |
| Bundibugyo ebolavirus | Identified in Uganda with moderate mortality |
| Reston ebolavirus | Found in Asia, non-pathogenic to humans |
| Bombali ebolavirus | Discovered recently, role in human disease unclear |
Classification aids in understanding outbreak patterns and developing targeted treatments or vaccines.
Transmission and Spread
Ebola Virus Disease (EVD) spreads through specific interactions with infected materials and hosts. The virus has natural animal reservoirs and primarily transmits via direct contact with bodily fluids. Human-to-human transmission occurs mainly in close physical settings.
Modes of Transmission
The Ebola virus transmits through direct contact with infected blood, saliva, sweat, urine, feces, vomit, breast milk, or semen. It enters the body via broken skin or through mucous membranes such as the eyes, nose, or mouth. Contact with contaminated surfaces, clothing, bedding, or medical equipment can also facilitate transmission. In healthcare settings, the reuse of needles or syringes without proper sterilization has historically contributed to the spread of the virus. Importantly, Ebola is not transmitted through air or water; infection requires close and direct contact with infectious materials. Deceased individuals who had EVD remain highly contagious, and their bodies can transmit the virus until they are safely buried or cremated following strict infection prevention protocols.
Reservoirs and Zoonotic Origins
Fruit bats of the Pteropodidae family are considered the primary natural reservoirs of the Ebola virus. These bats carry the virus without exhibiting symptoms, enabling its persistence in nature. They can transmit the virus to other wildlife, including non-human primates such as chimpanzees and gorillas, as well as forest antelope. Zoonotic transmission to humans typically occurs when people handle or consume infected animals, particularly through hunting, butchering, or preparing bushmeat. Such spillover events often occur in rural or forested regions where human populations live in close proximity to wildlife habitats. Once the virus enters human populations through these routes, it can cause localized outbreaks that may escalate into larger epidemics if not contained.
Human-to-Human Spread
After human infection occurs, the virus spreads primarily through direct contact with the bodily fluids of symptomatic individuals. Family members, caregivers, and healthcare workers face the greatest risk due to the likelihood of close physical contact. Outbreaks are often amplified in hospitals and clinics lacking adequate personal protective equipment, isolation facilities, or proper sanitation practices. Traditional funeral and burial customs, which may involve washing, touching, or kissing the body of the deceased, also significantly increase transmission risk. While individuals are not contagious during the incubation period, infectiousness begins once symptoms appear, and the risk of transmission rises with disease progression due to increasing viral load in bodily fluids.
Signs and Symptoms
Ebola Virus Disease presents a sequence of symptoms that develop from initial infection to critical illness. These symptoms are distinct and evolve through phases involving fever, systemic illness, and severe organ dysfunction.
Incubation Period
The incubation period ranges from 2 to 21 days, most often between 8 and 10 days after exposure. During this time, the virus multiplies in the body without causing any noticeable symptoms, and the infected individual is not yet contagious. The virus initially targets immune cells, particularly monocytes, macrophages, and dendritic cells, before spreading to multiple organs through the bloodstream. This asymptomatic phase poses challenges for outbreak control because exposed individuals may unknowingly travel or interact with others before illness begins.
Early Symptoms
The early phase of Ebola infection usually begins suddenly with high fever (above 38.3°C / 101°F), severe headache, muscle and joint pain, profound fatigue, and sore throat. Patients may also experience chills, loss of appetite, and general malaise.
Within a short period, often within the first few days, gastrointestinal symptoms such as vomiting, diarrhoea, and abdominal pain develop. These symptoms are non-specific and may resemble other tropical diseases such as malaria or typhoid fever, but they become more concerning when accompanied by a known exposure risk or when they appear in the context of an ongoing outbreak.
Advanced Symptoms
As EVD progresses, more severe manifestations appear. Patients may develop a maculopapular rash (flat or raised red spots) and signs of organ dysfunction, including impaired liver and kidney function. Laboratory tests during this phase often reveal elevated liver enzymes, reduced platelet counts, and electrolyte imbalances.
Bleeding (haemorrhage) may occur in severe cases, presenting as petechiae (small pinpoint spots), ecchymoses (bruises), or bleeding from mucous membranes such as the gums and nose. Internal bleeding may also occur, leading to blood in stools or vomit. In advanced disease, neurological symptoms such as confusion, disorientation, seizures, and coma may develop, often signalling poor prognosis.
Complications
Severe cases can lead to haemorrhagic shock caused by significant blood loss, or disseminated intravascular coagulation (DIC)—a condition where widespread clotting in the blood vessels is followed by uncontrolled bleeding. Organ failures, especially of the liver and kidneys, cause severe metabolic disturbances such as acidosis and electrolyte depletion.
Secondary bacterial or fungal infections are common due to a weakened immune system and breaches in protective barriers such as the skin and mucous membranes. These infections can accelerate deterioration. Once multi-organ failure sets in, mortality rates often exceed 50%, and survival becomes unlikely without intensive, specialized care.
Diagnosis of Ebola Virus Disease
Diagnosis of Ebola Virus Disease relies on a combination of clinical symptoms, patient history, and specific laboratory tests. Prompt and accurate identification is critical due to the disease’s severity and potential for outbreaks.
Laboratory Testing
Laboratory confirmation is the gold standard for diagnosing EVD. The most widely used and reliable method is reverse transcription-polymerase chain reaction (RT-PCR), which detects Ebola virus genetic material (RNA) in blood or other bodily fluids. RT-PCR can confirm infection within days of symptom onset, even when the virus is present in low amounts. In the early stages of infection, antigen-capture enzyme-linked immunosorbent assay (ELISA) can detect viral proteins, providing a complementary diagnostic option.
Although virus isolation in cell culture can confirm Ebola infection, it is rarely performed due to the high biosafety risks and the need for specialized biosafety level 4 (BSL-4) laboratories. In confirmed cases, laboratory testing may be repeated periodically to monitor viral load and to confirm when a patient has cleared the infection. Post-recovery testing of specific body fluids such as semen, breast milk, or ocular fluid may also be conducted, as the virus can persist in these fluids for months.
Clinical Evaluation
The clinical evaluation of suspected Ebola cases begins with identifying early symptoms such as sudden fever, fatigue, muscle aches, headache, and sore throat. These symptoms often progress to vomiting, diarrhoea, abdominal pain, and in some cases, rash or both internal and external bleeding. However, not all patients show signs of haemorrhage.
A thorough exposure history is crucial. This includes recent travel to or residence in an area with active Ebola transmission, contact with known or suspected cases, or participation in high-risk activities such as funeral rites involving direct handling of a body. The disease’s incubation period ranges from 2 to 21 days, and the appearance of symptoms within this window after a possible exposure is considered a strong indicator for further testing.
Differential Diagnosis
Ebola shares early symptoms with several other infectious diseases common in endemic regions, which can lead to misdiagnosis. These include malaria, typhoid fever, leptospirosis, and other viral haemorrhagic fevers such as Lassa fever and Marburg virus disease. In some areas, malaria is the primary suspicion due to its high prevalence and symptom overlap; however, it can be quickly ruled out with rapid diagnostic tests.
Accurate diagnosis requires considering local disease patterns, seasonal outbreaks, and detailed patient history. Laboratory testing for other haemorrhagic fevers often involves separate, virus-specific assays. Misdiagnosis or delays in confirming Ebola can lead to further transmission, making rapid testing and careful clinical evaluation critical components of outbreak control.
Treatment and Management
Treatment for Ebola Virus Disease focuses on maintaining vital functions and preventing complications. Various supportive and targeted therapies aim to improve survival rates and reduce symptom severity.
Supportive Care
Supportive care remains the primary and most widely available approach to managing EVD. It involves maintaining hydration through oral or, more often, intravenous (IV) fluids to prevent dehydration caused by vomiting and diarrhoea. Electrolyte replacement—restoring essential minerals like sodium and potassium—is crucial to prevent heart and muscle complications. In severe cases, oxygen therapy may be used to support breathing, especially if lung function is impaired.
Continuous monitoring of vital signs, such as heart rate, blood pressure, and oxygen saturation, enables healthcare providers to detect and respond to sudden changes in a patient’s condition. Treating secondary bacterial or fungal infections with antibiotics or antifungal drugs is a key part of supportive care, as Ebola patients are highly susceptible to other infections. Adequate nutrition, pain relief using analgesics, and management of fever are also provided to improve comfort and support recovery. Evidence suggests that starting supportive care early in the illness greatly increases the chances of survival.
Antiviral Therapies
Antiviral drugs aim to stop or slow the replication of the Ebola virus within the body. Remdesivir, which works by blocking the viral enzyme RNA polymerase, has been tested for Ebola treatment with mixed results, but it remains an option in certain settings. Favipiravir, another antiviral, interferes with viral replication and has been used experimentally in outbreaks, though its effectiveness varies depending on the stage of illness and viral load.
The most successful antiviral approaches so far have been monoclonal antibody therapies, such as REGN-EB3 and mAb114 (Ebanga), both of which have shown high survival rates when administered early. These antibodies work by binding to the Ebola virus surface proteins, preventing the virus from entering human cells. Such treatments are now recommended as part of standard Ebola care in outbreak situations, especially for confirmed cases diagnosed early.
Experimental Treatments
Research into Ebola treatments is ongoing, with several experimental options under development or evaluation. ZMapp, a combination of three monoclonal antibodies, was one of the earliest therapies to show promise, though later studies found it less effective than newer antibody-based drugs. Convalescent plasma therapy, which uses blood plasma from Ebola survivors containing natural antibodies, has been tested but results have been inconsistent, partly due to variations in antibody levels between donors.
Other experimental strategies include gene-editing technologies that target viral genetic material, as well as novel antivirals that block multiple stages of the Ebola life cycle. Some studies are exploring immune-modulating drugs that could help the body control the inflammatory response triggered by severe infection. Access to experimental treatments is generally restricted to clinical trials or outbreak response programs under emergency use protocols.
Prevention and Control Measures
Effective prevention and control of Ebola Virus Disease requires strict hygiene practices, vaccination campaigns, and organized responses during outbreaks. Each component is critical to reducing transmission and managing cases efficiently.
Infection Prevention Protocols
- Use of personal protective equipment (PPE): Healthcare workers should wear gloves, gowns, masks, and eye protection when caring for Ebola patients.
- Hand hygiene: Wash hands frequently with soap and water or use alcohol-based hand sanitizers, especially before and after patient contact.
- Isolation of patients: Confirmed and suspected cases should be treated in designated isolation or treatment units to minimize exposure.
- Disinfection of surfaces: Clean and disinfect contaminated areas, instruments, and materials using approved agents such as chlorine solutions.
- Safe burial practices: Handle the remains of deceased patients with minimal contact; trained burial teams should follow safety protocols to prevent infection.
Vaccination
The rVSV-ZEBOV vaccine, a recombinant vesicular stomatitis virus–based vaccine, is currently the most widely used preventive measure during Ebola outbreaks. It has demonstrated high efficacy when implemented in ring vaccination strategies, in which contacts of confirmed cases and their contacts are immunized to create a protective barrier against spread.
Vaccination efforts focus on individuals at highest risk, including healthcare personnel, laboratory workers handling Ebola specimens, frontline responders, and people living in areas with active transmission. Maintaining the cold chain—a system that keeps vaccines at the required temperature from manufacture to administration—is essential to preserve potency.
Although the vaccine is not given routinely to the general public, it is strategically deployed in outbreak zones to halt transmission rapidly. Additional research is ongoing to develop multi-strain vaccines that provide broader and longer-lasting protection.
Outbreak Response Strategies
Successful Ebola control depends on rapid detection and immediate intervention. Early case identification and isolation limit opportunities for the virus to spread in the community. Contact tracing teams monitor all individuals who may have been exposed to a confirmed patient for the full 21-day incubation period, enabling prompt treatment if symptoms develop.
Community engagement is critical to the effectiveness of outbreak control measures. Providing clear, culturally appropriate information in local languages builds trust, reduces misinformation, and encourages cooperation with health authorities.
Mobile treatment centers and rapid diagnostic testing improve access to care and speed up confirmation of cases, allowing public health teams to act quickly. Collaboration between local health systems, national governments, non-governmental organizations, and international agencies such as the World Health Organization (WHO) and Médecins Sans Frontières (MSF) ensures coordinated resource distribution, logistical support, and real-time data sharing to manage outbreaks effectively.
Prognosis and Outcomes
The prognosis of Ebola Virus Disease (EVD) varies widely depending on multiple factors, including the strain of the virus and the quality of medical care. Outcomes can range from full recovery to death, with many survivors experiencing lasting health issues.
Survival Rates
Case fatality rates for EVD vary between 25% and 90%, largely depending on the virus strain involved and the quality of care provided. The Zaire ebolavirus, considered the most virulent strain, has recorded fatality rates between 70% and 90% in some outbreaks. Early detection combined with supportive care—such as intravenous or oral fluid replacement, treatment of secondary infections, and management of symptoms like fever and diarrhoea—significantly improves chances of survival. Access to advanced facilities, including intensive care units and monitoring of organ function, further reduces mortality.
Vulnerable populations, including children, pregnant women, the elderly, and individuals with pre-existing health conditions, face higher risks of severe disease and death. Without adequate medical intervention, death typically occurs within 6 to 16 days from the onset of symptoms, often as a result of multi-organ failure, shock, or severe internal and external haemorrhaging.
Long-Term Effects
Many survivors develop a cluster of complications known as post-Ebola syndrome (PES), which may persist for months or years. Common symptoms include joint and muscle pain, chronic fatigue, headaches, and vision problems such as uveitis (inflammation of the eye). Hearing loss has also been reported in some cases. Neurological complications such as memory loss, difficulty concentrating, and nerve pain may occur, alongside psychological issues including anxiety, depression, and post-traumatic stress disorder (PTSD).
Survivors may also experience social stigma and economic hardship due to prolonged recovery periods and community misconceptions about the disease. Persistent virus in certain body fluids, such as semen, ocular fluid, and breast milk, can remain for months after recovery, posing a potential risk of transmission. As a result, follow-up testing, counselling, and sexual health guidance are recommended for survivors to prevent further spread and manage ongoing health problems.