Ebola (Ebola Hemorrhagic Fever or Ebola Virus Disease)

Ebola Virus Disease Facts

  • Ebola virus disease (EVD), also referred to as Ebola hemorrhagic fever, is a severe and often fatal disease in humans and nonhuman primates such as monkeys, chimpanzees, and gorillas.
  • Ebola virus disease is caused by Ebola virus, named after a river in the Democratic Republic of the Congo (formerly Zaire) in Africa, where it was first recognized.
  • Ebola virus disease outbreaks occur mainly in villages in Central and West Africa and have a mortality rate up to 90%.
  • The Ebola virus is thought to be transmitted to people from wild animals and spreads in the human population through human-to-human contact.
  • Symptoms of Ebola virus disease occur suddenly up to 21 days after exposure and include fever, headache, sore throat, joint and muscle aches, and weakness, followed by diarrhea, vomiting, and stomach pain. Some patients may bleed inside and outside the body.
  • A person is contagious when early symptoms start. Survivors remain contagious for 21-42 days after symptoms go away. Some patients have detectable virus in the semen and in the eyes for many months, but the contagious period related to this viral presence is not known.
  • Treatment is supportive care. There is no licensed drug or vaccine available, but experimental therapy is being tested.

What Is the History of Ebola Virus Disease?

The first Ebola virus species was discovered in 1976 in the Democratic Republic of the Congo (formerly Zaire) near the Ebola River, where it received its name. The first outbreak of Ebola virus disease infected 318 people and caused 280 deaths, with a mortality rate of 88%. A simultaneous outbreak occurred in Sudan and caused a mortality rate of 53%. Since then, sporadic outbreaks have occurred in Central and West Africa, with no cases reported between 1979 and 1994. In 1989, an Ebola virus strain, called Ebola-Reston, was introduced into Reston, Virginia, by infected monkeys imported from the Philippines. Fortunately, research workers who were exposed to the Ebola virus never developed symptoms of Ebola virus disease.

The latest and ongoing Ebola virus disease outbreak in West Africa was first reported in March 2014. It is considered the worst outbreak in Ebola virus history with a rising death toll in Guinea, Liberia, Sierra Leone, and Nigeria. There was concern that the large number of infected people in this epidemic would cause a pandemic (spread of the disease worldwide) because infected people transmitted the disease for the first time to several African countries, Europe, and the United States (Texas). Fortunately, the disease was eventually contained and the pandemic was avoided. As of 2015 (most recent statistical data from the U.S. Centers for Disease Control and Prevention [CDC]), there were almost 27,000 cases with over 11,000 deaths reported. Previous outbreaks had fewer than 500 cases per year according to CDC statistics.

What Are Ebola Virus Disease Causes and Risk Factors?

Ebola virus disease is caused by an infection with the Ebola virus, a member of the Filoviridae family. The Ebola virus has been found in African monkeys, chimpanzees, and other nonhuman primates. The natural reservoir (normal habitat) of Ebola viruses is unknown. However, researchers believe that the virus is zoonotic (animal-borne) with bats being the most likely reservoir.

There are five identified species (types) of Ebola virus. Four of the five have caused disease in humans:

  • Zaire ebolavirus
  • Sudan ebolavirus
  • Taï Forest ebolavirus
  • Bundibugyo ebolavirus
  • Reston ebolavirus (has not caused illness in humans)

The risk of getting Ebola virus disease is low for most people. All cases of illness or death have occurred in Africa, with the exception of laboratory contamination in Russia and England. The risk increases if a person travels to or lives in Africa where Ebola virus disease outbreaks have occurred. Those at highest risk include the following:

  • Health-care workers and family and friends who have cared for an infected person with Ebola virus disease
  • Laboratory personnel working with bodily fluids of an Ebola virus disease patient
  • Animal researchers with direct handling of bats, rodents, or primates from an area where Ebola virus disease has occurred
  • Individuals participating in funeral rites in which there is direct exposure to human remains where an Ebola virus disease outbreak is occurring

History of the Ebola Virus

In 1976, the Ebola virus was discovered in the Democratic Republic of Congo near the Ebola River.

Though there have been sporadic outbreaks since 1976, a 2014 outbreak in West Africa is the largest outbreak of the Ebola virus to date.

How Contagious Is Ebola, and How Long Is Someone With the Disease Contagious?

Ebola virus infection can be highly contagious. The person becomes contagious when the first symptoms, like fever, begin to appear until the person dies. The person who dies leaves a body that is extremely contagious until the body is cremated or buried. If an individual survives Ebola, the person remains contagious for approximately 21-42 days after the symptoms abate. However, Ebola viruses have been detected in men's semen for many months and in the eyes of males and females for months (Ebola survivors), but it is not clear how contagious the virus is in these locations.

What Is the Incubation Period for Ebola?

The incubation period for Ebola (time after initial infection with the virus to the appearance of first symptoms) varies from about two to 21 days, with an average incubation period of about eight to 10 days.

How Does the Ebola Virus Spread?

The Ebola virus is contagious after a person develops symptoms. How the virus first infects a human at the start of an outbreak is unknown but is thought to be from an infected animal transmitted to humans, either by direct contact (for example, fruit bats) or by eating wild animals like monkeys. The infected patient can then spread the virus in several ways to others. People can become exposed to the virus through direct contact with a sick person's blood or other body fluids, such as urine, saliva, feces, vomit, and semen. It can also be spread through objects, such as needles, contaminated with infected body fluids. During an Ebola virus disease outbreak, the virus can spread quickly in hospitals and clinics, especially if health-care workers are not wearing protective equipment such as masks, gowns, and gloves. Ebola virus is not spread through the air, by water, or food (with the notable exception of bushmeat that is defined as wild animals hunted for food), according to the CDC.

What Are Signs and Symptoms of Ebola Virus Disease?

Symptoms may appear anywhere from two to 21 days after exposure to Ebola virus, but eight to 10 days is most common. Typical signs and symptoms of Ebola virus disease include

These symptoms are followed by increasingly severe problems such as

Some patients may develop

Late signs include the following:

It is not known why some people survive from an infection with the Ebola virus. However, researchers have found that those who die from the disease are not able to develop an adequate immune response to the virus.

What Specialists Treat Ebola Virus Disease?

Although primary-care physicians and pediatricians may see patients with Ebola initially, these physicians (and emergency-medicine specialists) are urged by the CDC and World Health Organization to transfer Ebola-infected patients to special facilities that have physicians, support personnel, and isolation and/or intensive-care units that are especially trained to treat Ebola-infected patients. Specialists who will be consulted may include infectious-disease specialists, critical-care specialists, lung specialists, hematologists, hospitalists, travel-medicine specialists, infection-control specialists, and in the U.S., CDC personnel.

What Are Ebola Virus Disease Complications?

Ebola virus disease is a highly fatal illness with a survival rate of only 10%-50%. As the illness progresses, it can cause failure of multiple organs (such as the lung, kidney, and liver), severe bleeding inside and outside the body, jaundice, seizures, coma, and shock (low blood pressure). Researchers do not understand why some people survive and others do not. For those who do survive, recovery can be slow. They may develop inflammation of the eyes (uveitis), liver (hepatitis), or testicles (orchitis), as well as symptoms like, fatigue, weakness, chronic joint pains, or headaches.

What Tests Do Specialists Use to Diagnose Ebola Virus Disease?

Diagnosing Ebola virus disease in a patient in the first few days is difficult, because the signs and symptoms are similar to more common illnesses. If a patient has risk factors for exposure to the Ebola virus and is suspected to be infected with it, then samples from the patient can be collected to confirm the diagnosis.

Antigen-capture enzyme-linked immunosorbent assay (ELISA) testing, IgM ELISA, polymerase chain reaction (PCR) to identify the genetic material of the virus, and virus isolation are all laboratory tests that can be used to diagnose an infected person within a few days when symptoms begin. Patients tested later in their disease or after recovery can be tested for IgM and IgG antibodies (immune response proteins directed against a part of the virus). In those who have died, immunohistochemistry testing (using antibody-linked stains and microscopic examination to detect a part of the virus in cells of a tissue sample), virus isolation, or PCR can be done.

What Are Ebola Virus Disease Treatments?

Standard treatment for Ebola virus disease is still limited to supportive therapy in an intensive-care unit, which includes

  • intravenous (IV) fluids and electrolytes to treat dehydration,
  • maintaining blood pressure,
  • providing oxygen,
  • replacing blood through transfusions, and
  • treating additional infections that may develop subsequently.

What Medications Treat Ebola Virus Disease?

There is no medical cure for Ebola virus disease. Experimental treatments have been tested and proven effective in animal models, but clinical trials to test effectiveness in humans have not been done.

ZMapp, a drug being developed by Mapp Biopharmaceutical, Inc., for use with people infected with the Ebola virus, is a combination of three different monoclonal antibodies that bind to the proteins of the Ebola virus. The experimental drug has been given to two American missionaries who became infected with the Ebola virus while caring for sick patients in Liberia, and they have shown signs of recovery.

Another experimental drug, TKM-Ebola, is being developed by Tekmira Pharmaceuticals and resulted in 100% protection from the Ebola virus in animals. It may serve as a potential cure.

How Can People Prevent Ebola Virus Disease?

One way to prevent exposure to Ebola virus is to not travel to an area where the outbreak has occurred. Avoiding contact with a person infected with Ebola virus disease will also decrease risk. Ebola viruses can spread rapidly in hospitals and clinics even though they are generally considered to not be airborne. Patients suspected to have an infection with Ebola virus should be isolated immediately. Protective equipment, such as masks, goggles, gowns, and gloves, should be worn by medical personnel to prevent direct contact with blood or other body fluids. It is also important to avoid unprotected direct contact with the bodies of patients who have died of the disease because the body contains large amounts of highly contagious Ebola virus. Proper cleaning and disposal of instruments, such as needles and syringes, is also important.

Because the disease may be transmitted during sex, the CDC recommends avoiding contact with semen and/or vaginal fluid from anyone who has survived Ebola until there is more data available about the transmission of this disease.

There is no vaccine available for prevention of Ebola virus disease.

What Is the Prognosis for Ebola Virus Disease?

The overall prognosis of Ebola virus disease is poor. Infection with Ebola virus is associated with a high mortality up to 90%, with the exception of the Reston strain that has not caused illness in humans. The deadliest Ebola virus species is Zaire ebolavirus. Survivors may have long-lasting complications (see complications section above).

What Is the Latest Research on Ebola Virus Disease?

Research on vaccine and drug development has become a more urgent issue due to the recently large outbreak of Ebola in Africa. Studies in animals have shown effectiveness in treating Ebola virus disease. The U.S. National Institutes of Health (NIH) is expediting their work on an Ebola vaccine with launching of clinical trials. New experimental drugs in addition to ZMapp and TKM-Ebola are being developed. Other Ebola research includes developing tools to assist in early diagnosis of Ebola virus disease, increasing knowledge of the natural reservoir (habitat) of Ebola virus, and understanding how it is spread.

Ebola Virus Disease Picture

Picture of an Ebola virus virion
Picture of an Ebola virus virion; SOURCE: CDC/Cynthia Goldsmith

Where Can People Get More Information on Ebola Virus Disease?

For more information, visit CDC's and WHO's web site on Ebola at http://www.cdc.gov/vhf/ebola/ and http://www.who.int/mediacentre/factsheets/fs103/en/.

Reviewed on 11/21/2017


United States. Centers for Disease Control and Prevention. "Ebola (Ebola Virus Disease)." June 22, 2016. <http://www.cdc.gov/vhf/ebola/>.

World Health Organization. "Ebola Virus Disease." Apr. 2014. <http://www.who.int/mediacentre/factsheets/fs103/en/>.

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