Ebola hemorrhagic fever is caused by a virus. It is a severe and often fatal disease. It can affect humans and other primates. Researchers believe that the virus first spreads from an infected animal to a human. It can then spread from human to human through direct contact with a patient's blood or secretions.

Symptoms of Ebola may appear anywhere from 2 to 21 days after exposure to the virus. Symptoms usually include

• Fever
• Headache
• Joint and muscle aches
• Weakness
• Diarrhea
• Vomiting
• Stomach pain
• Lack of appetite

Other symptoms including rash, red eyes, and internal and external bleeding, may also occur.

The early symptoms of Ebola are similar to other, more common, diseases. This makes it difficult to diagnose Ebola in someone who has been infected for only a few days. However, if a person has the early symptoms of Ebola and there is reason to suspect Ebola, the patient should be isolated. It is also important to notify public health professionals. Lab tests can confirm whether the patient has Ebola.

There is no cure for Ebola. Treatment involves supportive care such as fluids, oxygen, and treatment of complications. Some people who get Ebola are able to recover, but many do not.

Ebola virus disease (EVD) is a deadly disease with occasional outbreaks that occur mostly on the African continent. EVD most commonly affects people and nonhuman primates (such as monkeys, gorillas, and chimpanzees). It is caused by an infection with a group of viruses within the genus Ebolavirus:

• Ebola virus (species Zaire ebolavirus)
• Sudan virus (species Sudan ebolavirus)
• Taï Forest virus (species Taï Forest ebolavirus, formerly Côte d’Ivoire ebolavirus)
• Bundibugyo virus (species Bundibugyo ebolavirus)
• Reston virus (species Reston ebolavirus)
• Bombali virus (species Bombali ebolavirus)

Of these, only four (Ebola, Sudan, Taï Forest, and Bundibugyo viruses) have caused disease in people. Reston virus can cause disease in nonhuman primates and pigs, but there have not been cases in people. Bombali virus was first identified in bats in 2018, and experts do not know yet if it causes disease in either animals or people.

Ebola virus was first discovered in 1976 near the Ebola River in what is now the Democratic Republic of Congo. Since then, the virus has been infecting people from time to time, leading to outbreaks in several African countries. Scientists do not know where Ebola virus comes from. Based on similar viruses, they believe EVD is animal-borne, with bats or nonhuman primates being the most likely source. Infected animals carrying the virus can transmit it to other animals, like apes, monkeys, duikers and humans.

The virus first spreads to people through direct contact with the blood, body fluids and tissues of animals. Ebola virus then spreads to other people through direct contact with body fluids of a person who is sick with or has died from EVD. This can occur when a person touches these infected body fluids or objects that are contaminated with them. The virus then gets into the body through broken skin or mucous membranes in the eyes, nose, or mouth. People can get the virus through sexual contact with someone who is sick with or has recovered from EVD. The virus can persist in certain body fluids, like semen, after recovery from the illness.

Ebola survivors may experience side effects after their recovery. These may include tiredness, muscle aches, eye and vision problems and stomach pain.

Emergence of Ebola in Humans

Ebola virus disease (EVD), one of the deadliest viral diseases, was discovered in 1976 when two consecutive outbreaks of fatal hemorrhagic fever occurred in different parts of Central Africa. The first outbreak occurred in the Democratic Republic of Congo (formerly Zaire) in a village near the Ebola River, which gave the virus its name. The second outbreak occurred in what is now South Sudan, approximately 500 miles (850 km) away.

Initially, public health officials assumed these outbreaks were a single event associated with an infected person who traveled between the two locations. However, scientists later discovered that the two outbreaks were caused by two genetically distinct viruses: Zaire ebolavirus and Sudan ebolavirus. After this discovery, scientists concluded that the virus came from two different sources and spread independently to people in each of the affected areas.

Viral and epidemiologic data suggest that Ebola virus existed long before these recorded outbreaks occurred. Factors like population growth, encroachment into forested areas, and direct interaction with wildlife (such as bushmeat consumption) may have contributed to the spread of the Ebola virus.

Since its discovery in 1976, the majority of cases and outbreaks of Ebola Virus Disease have occurred in Africa. The 2014-2016 Ebola outbreak in West Africa began in a rural setting of southeastern Guinea, spread to urban areas and across borders within weeks, and became a global epidemic within months.

Identifying a Host

Following the discovery of the virus, scientists studied thousands of animals, insects, and plants in search of its source (called reservoir among virologists, people who study viruses). Gorillas, chimpanzees, and other mammals may be implicated when the first cases of an EVD outbreak in people occur. However, they – like people – are “dead-end” hosts, meaning the organism dies following the infection and does not survive and spread the virus to other animals. Like other viruses of its kind, it is possible that the reservoir host animal of Ebola virus does not experience acute illness despite the virus being present in its organs, tissues, and blood. Thus, the virus is likely maintained in the environment by spreading from host to host or through intermediate hosts or vectors.

African fruit bats are likely involved in the spread of Ebola virus and may even be the source animal (reservoir host). Scientists continue to search for conclusive evidence of the bat’s role in transmission of Ebola. The most recent Ebola virus to be detected, Bombali virus, was identified in samples from bats collected in Sierra Leone.

Understanding Pathways of Transmission

The use of contaminated needles and syringes during the earliest outbreaks enabled transmission and amplification of Ebola virus. During the first outbreak in Zaire (now Democratic Republic of Congo – DRC), nurses in the Yambuku mission hospital reportedly used five syringes for 300 to 600 patients a day. Close contact with infected blood, reuse of contaminated needles, and improper nursing techniques were the source for much of the human-to-human transmission during early Ebola outbreaks.

In 1989, Reston ebolavirus was discovered in research monkeys imported from the Philippines into the U.S. Later, scientists confirmed that the virus spread throughout the monkey population through droplets in the air (aerosolized transmission) in the facility. However, such airborne transmission is not proven to be a significant factor in human outbreaks of Ebola.The discovery of the Reston virus in these monkeys from the Philippines revealed that Ebola was no longer confined to African settings, but was present in Asia as well.

By the 1994 Cote d’Ivoire outbreak, scientists and public health officials had a better understanding of how Ebola virus spreads and progress was made to reduce transmission through the use of face masks, gloves and gowns for healthcare personnel. In addition, the use of disposable equipment, such as needles, was introduced.

During the 1995 Kikwit, Zaire (now DRC) outbreak, the international public health community played a strong role, as it was now widely agreed that containment and control of Ebola virus were paramount in ending outbreaks. The local community was educated on how the disease spreads; the hospital was properly staffed and stocked with necessary equipment; and healthcare personnel was trained on disease reporting, patient case identification, and methods for reducing transmission in the healthcare setting.

In the 2014-2015 Ebola outbreak in West Africa, healthcare workers represented only 3.9% of all confirmed and probable cases of EVD in Sierra Leone, Liberia, and Guinea combined.In comparison, healthcare workers accounted for 25% of all infections during the 1995 outbreak in Kikwit.During the 2014-2015 West Africa outbreak, the majority of transmission events were between family members (74%). Direct contact with the bodies of those who died from EVD proved to be one of the most dangerous – and effective – methods of transmission. Changes in behaviors related to mourning and burial, along with the adoption of safe burial practices, were critical in controlling that epidemic.

Ebola virus disease (EVD) is a very rare disease that can cause illness in people. It is believed to occur naturally in specific animal populations that live in multiple sub-Saharan African countries. In the areas where EVD is most common, Ebola virus is believed to spread at low rates among certain animal populations. Occasionally people become sick with Ebola after coming into contact with infected animals, which can lead to Ebola outbreaks in people who come in contact with them or others who have EVD.

When living in or traveling to a region where Ebola virus is potentially present, there are a number of ways to protect yourself and prevent the spread of EVD.

• Avoid contact with blood and body fluids (such as urine, feces, saliva, sweat, vomit, breast milk, amniotic fluid, semen, and vaginal fluids) of people who are sick.
• Avoid contact with semen from a man who has recovered from EVD, until testing shows that the virus is gone from his semen.
• Avoid contact with items that may have come in contact with an infected person’s blood or body fluids (such as clothes, bedding, needles, and medical equipment).
• Avoid funeral or burial practices that involve touching the body of someone who died from EVD or suspect EVD.
• Avoid contact with bats, forest antelopes, and nonhuman primates (such as monkeys and chimpanzees) blood, fluids, or raw meat prepared from these or unknown animals (bushmeat).

These same prevention methods should be used when living in or traveling to an area experiencing an Ebola outbreak. After returning from an area experiencing an Ebola outbreak, people should monitor their health for 21 days and seek medical care immediately if they develop symptoms of EVD.

Ebola Vaccine

The U.S. Food and Drug Administration (FDA) approved the Ebola vaccine rVSV-ZEBOV (called Ervebo) on December 19, 2019. This is the first FDA-approved vaccine for Ebola.

This vaccine is given as a single dose vaccine and has been found to be safe and protective against Zaire ebolavirus, which has caused the largest and most deadly Ebola outbreaks to date.

On February 26, 2020, the Advisory Committee on Immunization Practices (ACIP) recommended pre-exposure prophylaxis vaccination with rVSV-ZEBOV for adults ≥ 18 years of age in the U.S. population who are at potential occupational risk of exposure to Zaire ebolavirus. This recommendation includes adults who are

• Responding or planning to respond to an outbreak of EVD
• Laboratorians or other staff working at biosafety-level 4 facilities that work with live Ebola virus in the United States
• Healthcare personnel working at federally designated Ebola Treatment Centers in the United States

A two-dose vaccine regimen of a different vaccine that was also designed to protect against the Zaire ebolavirus species of Ebola was used under a research protocol in 2019 during an Ebola outbreak in the Democratic Republic of the Congo. The two doses of this vaccine use two different vaccine components (Ad26.ZEBOV and MVA-BN-Filo) and the regimen requires an initial dose and a “booster” dose 56 days later. This vaccine has not yet been approved by the FDA for routine use.

Ebola virus spreads through direct contact with the blood or body fluids of an infected person. The virus from blood and body fluids can enter the body through broken skin or mucous membranes in the eyes, nose, or mouth. This can easily happen by touching one’s face with contaminated hands.

Hand hygiene (including alcohol-based hand rubs, soap and water, and correct glove use) is a basic component of personal and community hygiene and is an important way to prevent the spread of infections while providing healthcare. Correct hand hygiene lowers the number of germs on the hands and limits the opportunity for spread, including for dangerous germs, like Ebola virus.

Proper hand hygiene methods are described below. Alcohol-based hand sanitizers are the preferred method for cleaning your hands in most clinical situations. When hands are visibly soiled with blood or other body fluids, wash hands with soap and water.

• Use alcohol-based hand sanitizer when hands are not visibly soiled. These products usually contain 60-95% ethanol or isopropanol. Alcohol-based hand sanitizer should not be used when hands are visibly soiled with dirt, blood, or other body fluids.
• Use soap and water when hands are visibly soiled with dirt, blood, or other body fluids and as an alternative to alcohol-based hand sanitizer. Antimicrobial soaps are not proven to offer benefits over washing hands with plain soap (not containing antimicrobial compounds) and water.
• Use mild (0.05%) chlorine solution in settings where hand sanitizer and soap are not available. Repeated use of 0.05% chlorine solution can cause skin irritation.

Scientists think people are initially infected with Ebola virus through contact with an infected animal, such as a fruit bat or nonhuman primate. This is called a spillover event. After that, the virus spreads from person to person, potentially affecting a large number of people.

The virus spreads through direct contact (such as through broken skin or mucous membranes in the eyes, nose, or mouth) with:

• Blood or body fluids (urine, saliva, sweat, feces, vomit, breast milk, amniotic fluid, and semen) of a person who is sick with or has died from Ebola virus disease (EVD).
• Objects (such as clothes, bedding, needles, and medical equipment) contaminated with body fluids from a person who is sick with or has died from EVD.
• Infected fruit bats or nonhuman primates (such as apes and monkeys).
• Semen from a man who recovered from EVD (through oral, vaginal, or anal sex). The virus can remain in certain body fluids (including semen) of a patient who has recovered from EVD, even if they no longer have symptoms of severe illness. There is no evidence that Ebola can be spread through sex or other contact with vaginal fluids from a woman who has had Ebola.

When people become infected with Ebola, they do not start developing signs or symptoms right away. This period between exposure to an illness and having symptoms is known as the incubation period. A person can only spread Ebola to other people after they develop signs and symptoms of Ebola.

Additionally, Ebola virus is not known to be transmitted through food. However, in certain parts of the world, Ebola virus may spread through the handling and consumption of wild animal meat or hunted wild animals infected with Ebola. There is no evidence that mosquitoes or other insects can transmit Ebola virus.

Risk

• Health workers who do not use proper infection control while caring for Ebola patients, and family and friends in close contact with Ebola patients, are at the highest risk of getting sick. Ebola can spread when people come into contact with infected blood or body fluids.
• Ebola poses little risk to travelers or the general public who have not cared for or been in close contact (within 3 feet or 1 meter) with someone sick with Ebola.

Persistence of the virus

The virus can remain in areas of the body that are immunologically privileged sites after acute infection. These are sites where viruses and pathogens, like the Ebola virus, are shielded from the survivor’s immune system, even after being cleared elsewhere in the body. These areas include the testes, interior of the eyes, placenta, and central nervous system, particularly the cerebrospinal fluid. Whether the virus is present in these body parts and for how long varies by survivor. Scientists are now studying how long the virus stays in these body fluids among Ebola survivors.

During an Ebola outbreak, the virus can spread quickly within healthcare settings (such as clinics or hospitals). Clinicians and other healthcare personnel providing care should use dedicated, preferably disposable, medical equipment. Proper cleaning and disposal of instruments such as needles and syringes are important. If instruments are not disposable, they must be sterilized before using again.

Ebola virus can survive on dry surfaces, like doorknobs and countertops for several hours; in body fluids like blood, the virus can survive up to several days at room temperature. Cleaning and disinfection should be performed using a hospital-grade disinfectant.

Symptoms may appear anywhere from 2 to 21 days after contact with the virus, with an average of 8 to 10 days. The course of the illness typically progresses from “dry” symptoms initially (such as fever, aches and pains, and fatigue), and then progresses to “wet” symptoms (such as diarrhea and vomiting) as the person becomes sicker.

Primary signs and symptoms of Ebola often include some or several of the following:

• Fever
• Aches and pains, such as severe headache and muscle and joint pain
• Weakness and fatigue
• Sore throat
• Loss of appetite
• Gastrointestinal symptoms including abdominal pain, diarrhea, and vomiting
• Unexplained hemorrhaging, bleeding or bruising

Other symptoms may include red eyes, skin rash, and hiccups (late-stage).

Many common illnesses can have the same symptoms as EVD, including influenza (flu), malaria, or typhoid fever.

EVD is a rare but severe and often deadly disease. Recovery from EVD depends on good supportive clinical care and the patient’s immune response. Studies show that survivors of Ebola virus infection have antibodies (proteins made by the immune system that identify and neutralize invading viruses) that can be detected in the blood up to 10 years after recovery. Survivors are thought to have some protective immunity to the type of Ebola that sickened them.

Diagnosing Ebola virus disease (EVD) shortly after infection can be difficult. Early symptoms of EVD such as fever, headache, and weakness are not specific to Ebola virus infection and often are seen in patients with other more common diseases, like malaria and typhoid fever.

To determine whether EVD is a possible diagnosis, there must be a combination of symptoms suggestive of EVD AND a possible exposure to EVD within 21 days before the onset of symptoms. An exposure may include contact with:

• Blood or body fluids from a person sick with or who died from EVD
• Objects contaminated with blood or body fluids of a person sick with or who died from EVD
• Infected fruit bats and nonhuman primates (apes or monkeys)
• Semen from a man who has recovered from EVD

If a person shows signs of EVD and has had a possible exposure, he or she should be isolated (separated from other people) and public health authorities notified. Blood samples from the patient should be collected and tested to confirm infection. Ebola virus can be detected in blood after onset of symptoms. It may take up to three days after symptoms start for the virus to reach detectable levels.

Polymerase chain reaction (PCR) is one of the most commonly used diagnostic methods because of its ability to detect low levels of Ebola virus. PCR methods can detect the presence of a few virus particles in small amounts of blood, but the ability to detect the virus increases as the amount of virus increases during an active infection. When the virus is no longer present in great enough numbers in a patient’s blood, PCR methods will no longer be effective. Other methods, based on the detection of antibodies an EVD case produces to an infection, can then be used to confirm a patient’s exposure and infection by Ebola virus.

A positive laboratory test means that Ebola infection is confirmed. Public health authorities will conduct a public health investigation, including identifying and monitoring all possibly exposed contacts.

Therapeutics

There are currently two treatments approved by the U.S. Food and Drug Administration (FDA) to treat EVD caused by the Ebola virus, species Zaire ebolavirus, in adults and children. The first drug approved in October 2020, Inmazeb, is a combination of three monoclonal antibodies. The second drug, Ebanga, is a single monoclonal antibody and was approved in December 2020. Monoclonal antibodies (often abbreviated as mAbs) are proteins produced in a lab or other manufacturing facility that act like natural antibodies to stop a germ such as a virus from replicating after it has infected a person. These particular mAbs bind to a portion of the Ebola virus’s surface called the glycoprotein, which prevents the virus from entering a person’s cells.

Both of these treatments, along with two others, were evaluated in a randomized controlled trial during the 2018-2020 Ebola outbreak in the Democratic Republic of the Congo. Overall survival was much higher for patients receiving either of the two treatments that are now approved by the FDA. Neither Inmazeb nor Ebanga have been evaluated for efficacy against species other than Zaire ebolavirus.

Supportive Care

Whether or not other treatments are available, basic interventions can significantly improve chances of survival when provided early. These are referred to as supportive care, and include:

• Providing fluids and electrolytes (body salts) orally or through infusion into the vein (intravenously).
• Using medication to support blood pressure, reduce vomiting and diarrhea, and to manage fever and pain.
• Treating other infections, if they occur.

In the wake of the 2014 West African outbreak and 2018 Democratic Republic of the Congo outbreak, the two largest outbreaks of Ebola virus disease (EVD) to date, there are now more EVD survivors than ever before. This large number of survivors provides a chance to better understand how Ebola virus affects people who have recovered, and to advise survivors on how to take care of themselves and their communities.

Recovery from Ebola

Recovery from EVD depends on good supportive care and the patient’s immune response. Investigational treatments are also increasing overall survival.

Those who do recover develop antibodies that can last 10 years, possibly longer. Survivors are thought to have some protective immunity to the type of Ebola that sickened them. It is not known if people who recover are immune for life or if they can later become infected with a different species of Ebola virus. Some survivors may have long-term complications, such as joint and vision problems.

Health Concerns for Survivors of Ebola

In most cases, people who have completely recovered from EVD do not become reinfected. However, many survivors suffer from health issues after recovery from Ebola.

The most commonly reported complications are:

• Tiredness
• Headaches
• Muscle and joint pain
• Eye and vision problems (blurry vision, pain, redness, and light sensitivity)
• Weight gain
• Stomach pain or loss of appetite

Other health problems can include memory loss, neck swelling, dry mouth, tightness of the chest, hair loss, hearing problems (ringing in the ears and hearing loss), pain or tingling in the hands and feet, inflammation of the pericardium (tissue around the heart), inflammation of one or both testicles, changes in menstruation, impotence, decreased or lost interest in sex, difficulty falling or remaining asleep, depression, anxiety, and post-traumatic stress disorder (PTSD).

The timing of onset, severity, and duration of complications among EVD survivors are variable.

Persistence of Ebola Virus

The virus can remain in areas of the body that are immunologically privileged sites after acute infection. These are sites where viruses and pathogens, like the Ebola virus, are shielded from the survivor’s immune system, even after being cleared elsewhere in the body. These areas include the testes, interior of the eyes, placenta, and central nervous system, particularly the cerebrospinal fluid. Whether the virus is present in these body parts and for how long varies by survivor.

Scientists continue to study the long-term effects of Ebola virus infection, including viral persistence, to better understand how to provide treatment and care to EVD survivors.

What are Ebola and Marburg?

Ebola virus disease and Marburg virus disease are viral hemorrhagic fevers. These diseases damage organs and blood vessels and may cause death. A person can get infected with Ebola or Marburg viruses if they touch or handle the following:

• Body fluids from an infected person, such as blood, urine, saliva, sweat, feces, vomit, breast milk, semen, and others.
• Objects contaminated with the body fluids of an infected person, such as clothes, bedding, needles, and medical equipment.
• Infected wild animals, for example bats and primates, or their body fluids or meat (bushmeat).

Ebola and Marburg symptoms may start anywhere from 2 to 21 days after a person is infected (for Ebola, the average is 8-10 days) and may include sudden fever, chills, headache, body aches, and a rash on the chest, back, and stomach. As the person gets sicker, they can have nausea, vomiting, chest pain, sore throat, abdominal pain, and diarrhea.

People with Ebola or Marburg are at risk for internal bleeding, critically low blood pressure (shock), damage to multiple organs and organ systems (liver, pancreas, kidneys, brain), and death.

Who is at risk?

Most travelers have low chances of getting infected with Ebola or Marburg viruses.

Ebola and Marburg viruses are found in sub-Saharan Africa.

Travelers to sub-Saharan Africa who work closely with or visit areas with bats or non-human primates, such as monkeys, chimpanzees, and gorillas, may be more likely to get infected. For example, two tourists visiting Uganda in 2008 who were infected with Marburg virus were likely exposed while visiting a cave known for its large bat population. People who care for patients with Ebola or Marburg disease may also be more likely to get infected due to exposure to their blood or body fluids.

What can travelers do to prevent Ebola and Marburg?

You can protect yourself from infection by taking the following steps.

• Avoid close contact with sick people and blood or body fluids from all people
  • Do not kiss, hug, or share eating utensils or cups.
  • Don't touch items that may have blood or body fluids on them.
• Avoid animals when traveling
  • Don't touch live or dead animals.
  • Avoid markets or farms with animals.
  • Don't eat or handle meat from wild animals.
  • If you are traveling to work with animals, wear appropriate protective gear.
• Wash your hands
  • Wash hands often with soap and water. If soap and water aren’t available, use an alcohol-based hand sanitizer containing at least 60% alcohol.
  • Keep your hands away from your eyes, nose, and mouth. If you need to touch your face, make sure your hands are clean.
• Avoid touching dead bodies
  • Don’t participate in funeral activities that involve touching dead bodies, or touch items that have been in contact with dead bodies or have blood or body fluids on them.

After Travel

If you traveled and feel sick, particularly if you have a fever, talk to a healthcare provider and tell them about your travel. Avoid contact with other people while you are sick.