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What is Ebola virus disease?
Ebola is the name of a particularly aggressive virus capable of causing a potentially fatal hemorrhagic fever in humans and other primates (monkeys, gorillas, chimpanzees). The virus was first discovered in 1976 in what is now the Democratic Republic of the Congo, in Central Africa, where it was named after the Ebola River located near the site of the initial outbreak.
Ebola is a severe and often fatal disease, capable of spreading from person to person through direct contact with the blood or bodily secretions of an infected patient.
Symptoms of Ebola virus disease can appear anywhere from 2 to 21 days after exposure to the virus and typically include:
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Fever.
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Headache.
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Joint and muscle pain.
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Weakness.
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Diarrhea.
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Vomiting.
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Stomach pain.
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Loss of appetite.
Other symptoms can also occur, including:
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Skin rash.
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Red eyes.
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Internal and external bleeding (hemorrhage).
The initial symptoms of infection closely overlap with those of other, much more common illnesses, which makes timely diagnosis genuinely difficult. Diagnosis is generally confirmed through specific laboratory testing rather than symptoms alone.
There is currently no specific cure for Ebola. Treatment therefore relies on supportive care, including:
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Intravenous fluids.
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Oxygen therapy.
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Treatment of complications as they arise.
When considering the disease as a whole, including its high mortality rate, the rapid onset of debilitating symptoms, and the typical geographic isolation of outbreak areas, the overall risk of a global pandemic is generally considered low. That said, the virus’s extreme lethality means it has historically been recognized as having potential for misuse as a biological weapon, which is one of the reasons international health authorities continue to monitor and study it closely.
The Virus
The virus’s primary reservoir appears to be certain animal species, with bats believed to be the main natural host. Humans can contract the virus from infected animals.
Following this initial transmission from animals, the virus can then spread from person to person through contact with bodily fluids or contaminated needles.
How Is It Transmitted?
Since the primary animal reservoir has not yet been definitively confirmed with complete certainty, the exact way in which the very first human case in a given outbreak becomes infected remains somewhat unclear, though it is hypothesized to occur through direct contact with an infected animal.
From Animals to Humans
The virus may be transmitted to humans through exposure to the bodily fluids of an infected animal:
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Blood: the butchering or consumption of infected animals can spread the virus. Scientists who have worked with infected animals as part of their research have, in documented cases, contracted the virus this way.
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Waste products: tourists visiting certain African caves, as well as some mine workers, have been infected with the related Marburg virus, likely through contact with the feces or urine of infected bats.
From Person to Person
Infected individuals generally do not become contagious until they begin developing symptoms, which is an important distinction from some other infectious diseases where transmission can occur before symptom onset.
There is no evidence that Ebola virus can be spread through insect bites.
Once Ebola infection occurs in humans, there are several ways the virus can be transmitted to other people:
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Direct contact with the fluids and secretions of an infected person (saliva, blood, sweat, feces, urine, vomit, semen, and other bodily fluids).
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Exposure to objects (such as needles) that have been contaminated with infectious secretions.
The viruses responsible for this disease spread easily within families and groups of friends, since these individuals come into close contact with infectious secretions while caring for sick loved ones. During outbreaks (meaning localized epidemics), the disease can also spread rapidly within healthcare facilities, such as clinics and hospitals, if staff do not wear adequate protective equipment, including masks, gowns, and gloves. Medical centers in parts of Africa are often under-resourced to the point that needles and syringes must be reused, and some of the worst Ebola outbreaks in history have occurred as a direct result of contaminated injections.
Contagiousness persists for as long as blood, secretions, organs, or semen continue to contain the virus. Ebola virus has been isolated from semen for months after the onset of illness, and transmission through semen has been documented as long as 7 weeks after clinical recovery.
Food and Other Transmission Routes
Ebola virus is not spread through air, water, or food in general, although there have indeed been documented cases in parts of Africa involving transmission through the careless handling of bushmeat from wild animals that had come into contact with infected bats.
There is no evidence that mosquitoes or other insects can transmit Ebola virus, and only a small number of mammal species (including humans, bats, and non-human primates) have been shown to be capable of becoming infected with the virus.
Symptoms
The U.S. Centers for Disease Control and Prevention (CDC) has established the following criteria for identifying patients at risk of Ebola infection:
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Clinical criteria, including:
- Fever above 38.6°C (101.5°F).
- Headache.
- Muscle pain.
- Vomiting.
- Diarrhea.
- Abdominal pain.
- Unexplained bleeding.
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Epidemiological risk factors within the 21 days prior to symptom onset, such as:
- Contact with the blood or other bodily fluids, or human remains, of a patient known or suspected to have the infection.
- Residence in, or travel from, an affected area.
- Direct handling of bats or non-human primates originating from areas where the disease is endemic.
In the absence of both of these types of criteria, there is no reasonable cause for concern about infection. Let’s now look specifically at the main symptoms of the disease.
The average incubation period is approximately 8 to 12 days, though it can range from 2 to 21 days. The average interval between the appearance of the first symptoms and death ranges from 3 to 21 days, with an average of approximately 10 days in fatal cases.
The earliest symptoms that appear with Ebola infection include:
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Fever (present in 87 percent of patients).
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Sore throat.
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Skin rash (more visible in patients with lighter skin tones).
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Red eyes and conjunctivitis.
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Chills.
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Joint pain and muscle pain.
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General malaise.
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Weakness (present in 76 percent of patients).
After approximately 5 days, gastrointestinal symptoms can appear:
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Watery diarrhea (present in 66 percent of patients).
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Nausea and vomiting (present in 68 percent of patients).
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Abdominal pain.
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Loss of appetite (present in 65 percent of patients).
Along with other symptoms, including:
Some patients may also experience:
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Hiccups.
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Cough.
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Weight loss.
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Difficulty swallowing.
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Hemorrhaging (internal and external bleeding).
Hemorrhage is not always present, but when it does occur, it typically appears in a later stage of the illness, presenting as petechiae (small red or purple spots on the skin), bruising/hematomas, and unexplained bleeding following injections.
Patients who ultimately succumb to the disease typically develop more severe clinical signs from the very first days of illness. By contrast, in cases that end in recovery, patients may experience fever for several days before beginning to improve, usually around day 6 of illness, although a prolonged period of convalescence is still generally required even after this initial improvement.
Mortality among patients during the West African outbreak that began in 2014, one of the largest and most devastating Ebola outbreaks in recorded history, was approximately 71 percent overall (ranging from 46 percent in Nigeria to 69-72 percent in Guinea, Sierra Leone, and Liberia). Risk factors significantly associated with a fatal outcome in the affected African countries included:
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Age over 45 years.
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Unexplained bleeding.
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A range of other signs and symptoms, not all of which were universally present:
- Diarrhea.
- Chest pain.
- Cough.
- Difficulty breathing.
- Difficulty swallowing.
- Conjunctivitis.
- Sore throat.
- Confusion.
- Hiccups.
- Coma or loss of consciousness.
Pregnant women, unfortunately, are generally subject to a very high risk of miscarriage when infected with Ebola virus.
For those who do survive, recovery is typically slow. It can take months to regain lost weight and strength, and the virus can remain present within the body, particularly in certain bodily fluids and immune-privileged sites, for many months following clinical recovery.
Dangers and Complications
The mortality rate associated with Ebola virus disease is extremely high, ranging from 50 to 89 percent depending on the specific viral strain involved, one of the highest case fatality rates of any known human infectious disease.
As the disease progresses, it can cause:
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Failure of multiple organs.
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Severe hemorrhaging.
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Delirium.
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Seizures.
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Shock.
Researchers have also identified what is known as post-Ebola virus syndrome, a condition capable of affecting patients who have survived the acute infection. This syndrome presents with the appearance of symptoms including:
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Joint pain.
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Muscle pain.
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Eye problems (including, in some cases, blindness).
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Neurological disturbances.
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Severe fatigue.
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Hearing loss.
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Hair loss.
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Changes to the menstrual cycle.
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A general worsening of long-term health status.
This post-recovery syndrome, sometimes referred to as “post-Ebola syndrome”, has become an area of increasing research interest following recent outbreaks, since survivors represent a growing population whose long-term health needs require ongoing medical attention and support, often for years following their initial recovery from the acute infection.
Diagnosis
Early diagnosis of the disease is genuinely difficult, since initial symptoms such as red eyes and skin rash are nonspecific and are frequently seen in patients with far more common illnesses.
Laboratory tests used in diagnosis include:
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Within a few days after symptoms begin:
- ELISA (Enzyme-Linked ImmunoSorbent Assay) testing.
- IgM antibody testing.
- PCR (polymerase chain reaction) testing.
- Virus isolation.
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Later in the course of illness, or following hospitalization:
- IgM and IgG antibody testing.
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In deceased patients:
- Immunohistochemistry testing.
- PCR testing.
- Virus isolation.
Because these tests require specialized laboratory facilities and strict biosafety precautions given the extremely infectious nature of samples, diagnostic testing for Ebola is generally performed only at reference laboratories equipped to handle such high-risk pathogens safely.
Treatment and Therapy
Unfortunately, standard treatment for Ebola remains limited to supportive care and symptom management, since no specific antiviral cure currently exists for widespread clinical use. This supportive approach includes:
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Administration of fluids and electrolytes through intravenous therapy.
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Continuous maintenance of adequate oxygenation and blood pressure, potentially including blood transfusions when needed.
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Treatment of any secondary infections that may develop.
Beginning treatment promptly is genuinely important for improving outcomes, but unfortunately this is not always straightforward, since early diagnosis is not always possible given the nonspecific nature of initial symptoms.
It is worth noting that in recent years, significant progress has been made in developing targeted treatments for Ebola. Two monoclonal antibody therapies, Inmazeb (a combination of three monoclonal antibodies) and Ebanga (ansuvimab), have received regulatory approval in the United States specifically for the treatment of Zaire ebolavirus infection in adults and children, representing an important step forward from purely supportive care. These treatments work by targeting and neutralizing the virus itself, and their use, when available, has been associated with improved survival rates in treated patients, particularly when administered early in the course of illness.
Prevention
Preventing the disease presents numerous challenges. Since the exact route of initial transmission from animals to humans remains somewhat unclear, specific guidelines have been developed for healthcare workers to follow upon the identification of the first cases in an outbreak. In practical terms, however, isolating the sick individual remains essential for protecting family members and friends from infection.
It is also worth remembering, for those traveling to affected regions:
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Avoid traveling to areas with known active outbreaks.
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Wash your hands frequently, using soap and water or alcohol-based hand sanitizer containing at least 60 percent alcohol.
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Avoid bushmeat (meat from wild animals) in developing countries where outbreaks have occurred.
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Avoid contact with infected individuals.
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Do not handle the remains of patients who have died from Ebola.
Vaccine
On November 11, 2019, the first vaccine against Ebola was officially authorized for market use in the European Union. This vaccine, marketed under the brand name Ervebo (produced by Merck Sharp & Dohme B.V.), had been under study since 2014, the year the most severe Ebola outbreak in recent history erupted in West Africa.
This represented a conditional authorization, which allowed for a streamlined approval process compared to the standard pathway, given the pressing need to find an effective preventive solution to the ongoing epidemic emergency. This type of accelerated authorization is reserved for specific situations in which the benefit of immediate availability outweighs the risk associated with still-incomplete data, generally applying to medications aimed at treating, preventing, or diagnosing severely debilitating or potentially fatal diseases.
In other words, the vaccine was, at the time, still considered to be under investigation (it was deployed in the Democratic Republic of the Congo, where the mortality rate associated with infection at the time was approximately 67 percent). However, according to the World Health Organization, it was deemed sufficiently effective and safe to warrant broader use. Available data at the time indicated an immunization efficacy of approximately 97.5 percent among vaccinated patients.
Current safety information identifies the most common side effects as the classic reactions associated with injectable vaccines in general, including:
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Pain, swelling, and redness at the injection site.
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Headache.
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Fever.
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Muscle and joint pain.
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Fatigue.
A second vaccine, produced by Johnson & Johnson (administered as a two-dose regimen), was approved in July 2020, and numerous additional vaccine candidates continue to be studied as part of the ongoing global effort to strengthen defenses against future Ebola outbreaks.
Frequently Asked Questions
Can Ebola spread through the air like the flu or COVID-19?
No, Ebola is not an airborne virus. It spreads through direct contact with the blood or bodily fluids of an infected, symptomatic person, or through contact with contaminated objects such as needles. This is a fundamentally important distinction from respiratory viruses, and it is one of the key reasons why, despite its high mortality rate, Ebola has historically caused localized outbreaks rather than sustained global pandemics.
How long does someone remain contagious after recovering from Ebola?
Survivors can continue to carry the virus in certain body fluids, particularly semen, for an extended period after clinical recovery, with documented transmission through semen occurring as long as several weeks to months after recovery. For this reason, survivors are generally advised to practice safe sex and undergo follow-up testing for a period of time after recovery.
What should I do if I have recently traveled to a region with an Ebola outbreak and start feeling unwell?
If you develop fever or other compatible symptoms within 21 days of returning from an area with an active Ebola outbreak, you should seek medical attention immediately and inform healthcare providers of your recent travel history before arriving at a facility, so that appropriate precautions can be taken to protect both you and others.
Is there truly no cure for Ebola?
While there is no single universal “cure”, significant progress has been made in recent years. Two monoclonal antibody treatments have received regulatory approval specifically for Ebola caused by the Zaire ebolavirus species, and these treatments, combined with early and aggressive supportive care, have been shown to meaningfully improve survival rates when administered promptly.
How effective is the Ebola vaccine, and who should receive it?
The Ervebo vaccine has demonstrated high effectiveness, with studies indicating protection rates around 97.5 percent among vaccinated individuals. It is primarily recommended for people at high risk of exposure, including healthcare workers in affected regions and individuals living in or near active outbreak areas, rather than for general use among the broader public in non-endemic countries.
Why do Ebola outbreaks tend to stay localized rather than spreading globally?
Several factors contribute to this pattern, including the fact that infected individuals typically become severely ill very quickly, making long-distance travel unlikely; the relatively short window during which the virus survives outside the body; the fact that transmission requires direct contact with bodily fluids rather than airborne spread; and the geographic isolation of most historical outbreak locations, which are typically far from major international transportation hubs.
