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Views Articles Everything known so far about Ebola virus disease

Everything known so far about Ebola virus disease


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Ebola virus disease (EVD) or Ebola haemorrhagic fever (EHF) is a disease traced in human beings and primates caused by an ebolavirus. Symptoms start 2 days to 3 weeks after contracting the virus, with a fever, sore throat, muscle pain and headaches. Typically, vomiting, diarrhoea and rash follow, along with decreased functioning of the liver and kidneys. Around this time, affected people may begin to bleed both within the body and externally.

The virus may be acquired upon contact with blood or bodily fluids of an infected animal. Spreading through the air has not been documented in the natural environment. Fruit bats are believed to carry and spread the virus without being affected. Once human infection occurs, the disease may spread between people, as well. Male survivors may be able to transmit the disease via semen for nearly two months. To make the diagnosis, typically other diseases with similar symptoms such as malaria, cholera and other viral hemorrhagic fevers are first excluded. To confirm the diagnosis, blood samples are tested for viral antibodies, viral RNA, or the virus itself.

Prevention includes decreasing the spread of disease from infected animals to humans. This may be done by checking such animals for infection and killing and properly disposing of the bodies if the disease is discovered. Properly cooking meat and wearing protective clothing when handling meat may also be helpful, as are wearing protective clothing and washing hands when around a person with the disease. Samples of bodily fluids and tissues from people with the disease should be handled with special caution.

No specific treatment for the disease is yet available. Efforts to help those who are infected are supportive and include giving either oral rehydration therapy (slightly sweet and salty water to drink) or intravenous fluids. The disease has a high risk of death, killing between 50% and 90% of those infected with the virus. EVD was first identified in Sudan (now South Sudan) and the Democratic Republic of the Congo. The disease typically occurs in outbreaks in tropical regions of sub-Saharan Africa. From 1976 (when it was first identified) through 2013, the World Health Organization reported a total of 1,716 cases. The largest outbreak to date is the ongoing 2014 West Africa Ebola outbreak, which is affecting Guinea, Sierra Leone, Liberia and Nigeria. As of 22 August 2014, 2,615 suspected cases resulting in the deaths of 1,427 have been reported. Efforts are under way to develop a vaccine; however, none yet exists.

Signs and Symptoms

Symptoms of Ebola  typically include

  • Fever (greater than 38.6°C or 101.5°F)
  • Severe headache
  • Muscle pain
  • Weakness
  • Diarrhoea
  • Vomiting
  • Abdominal (stomach) pain
  • Lack of appetite

Symptoms may appear anywhere from 2 to 21 days after exposure to ebolavirus, although 8-10 days is most common.

symptoms-infographicSome who become sick with Ebola are able to recover. We do not yet fully understand why. However, patients who die usually have not developed a significant immune response to the virus at the time of death.


Because the natural reservoir of ebolaviruses has not yet been proven, the manner in which the virus first appears in a human at the start of an outbreak is unknown. However, researchers have hypothesized that the first patient becomes infected through contact with an infected animal.

When an infection does occur in humans, the virus can be spread in several ways to others. The virus is spread through direct contact (through broken skin or mucous membranes) with

  • a sick person’s blood or body fluids (urine, saliva, feces, vomit, and semen)
  • objects (such as needles) that have been contaminated with infected body fluids
  • infected animals

Healthcare workers and the family and friends in close contact with Ebola patients are at the highest risk of getting sick because they may come in contact with infected blood or body fluids.

During outbreaks of Ebola HF, the disease can spread quickly within healthcare settings (such as a clinic or hospital). Exposure to ebolaviruses can occur in healthcare settings where hospital staff are not wearing appropriate protective equipment, such as masks, gowns, and gloves.

Proper cleaning and disposal of instruments, such as needles and syringes, is also important. If instruments are not disposable, they must be sterilized before being used again. Without adequate sterilization of the instruments, virus transmission can continue and amplify an outbreak.

Risk of Exposure

Ebola viruses are found in several African countries. The first Ebola virus was discovered in 1976 near the Ebola River in what is now the Democratic Republic of the Congo. Since then, outbreaks of Ebola among humans have appeared sporadically in Africa.


house1Risk assessment in disease-endemic areas is difficult because the natural reservoir host of ebolaviruses, and the manner in which transmission of the virus to humans occurs remains unknown.

  • All cases of human illness or death have occurred in Africa (with the exception of several laboratory contamination cases: one in England and two in Russia)
    • No cases have been reported in the United States
    • In 2014, two U.S. healthcare workers who were infected with Ebola virus in Liberia were transported to a hospital in the United States.
  • Those at highest risk include
    • Healthcare workers
    • Family and friends of patients with Ebola

Healthcare workers in Africa should consult the Infection Control for Viral Hemorrhagic Fevers in the African Health Care Setting to learn how to prevent and control infections in these setting. Medical professionals in the United States should consult the Interim Guidance for Managing Patients with Suspected Viral Hemorrhagic Fever in U.S. Hospitals[PDF – 4 pages] .

Past Ebola Outbreaks

Past Ebola outbreaks have occurred in the following countries:

  • Democratic Republic of the Congo (DRC)
  • Gabon
  • South Sudan
  • Ivory Coast
  • Uganda
  • Republic of the Congo (ROC)
  • South Africa (imported)

Current Ebola Outbreak in West Africa

The current (2014) Ebola outbreak is occurring in the following West African countries:

  • Guinea
  • Liberia
  • Sierra Leone
  • Nigeria

Ebola Outbreaks 2000-2014

This section has archived postings of outbreaks that have occurred since the year 2000.

2014: Ebola Hemorrhagic Fever Outbreak in West Africa (Guinea, Liberia, Sierra Leone, and Nigeria)

The 2014 Ebola outbreak is one of the largest Ebola outbreaks in history and the first in West Africa. It is affecting four countries in West Africa: Guinea, Liberia, Nigeria, and Sierra Leone, but does not pose a significant risk to the U.S. public. CDC is working with other U.S. government agencies, the World Health Organization, and other domestic and international partners in an international response to the current Ebola outbreak in West Africa. CDC has activated its Emergency Operations Center (EOC) to help coordinate technical assistance and control activities with partners. CDC has deployed several teams of public health experts to the West Africa region and plans to send additional public health experts to the affected countries to expand current response activities.

Latest CDC Outbreak Information
Updated August 22, 2014

2012: Ebola Hemorrhagic Fever Outbreak in Uganda

As of December 2, 2012, the Ugandan Ministry of Health reported 7 cumulative cases (probable and confirmed) of Ebola virus infection, including 4 deaths, in the Luwero District of central Uganda. CDC assisted the Ministry of Health in the epidemiologic and diagnostic aspects of the outbreak. Testing of samples by CDC’s Viral Special Pathogens Branch took place at the Uganda Virus Research Institute in Entebbe. Reported numbers are subject to change.

2012: Ebola Hemorrhagic Fever Outbreak in Democratic Republic of Congo

The DRC Ministry of Health has declared an end to the most recent Ebola outbreak in DRC’s Province Orientale. The November 26 Press Release reports a final total of 77 cases, including 36 laboratory-confirmed cases, 17 probable and 24 suspect cases, with a total of 36 deaths. CDC assisted the Ministry of Health in the epidemiologic and diagnostic aspects of the investigation. Laboratory support was provided both through CDC’s field laboratory in Isiro, and through the CDC/UVRI lab in Uganda. The Public Health Agency of Canada (PHAC) also provides diagnostic support through its field lab in Isiro. The outbreak in DRC has no epidemiologic link to the near contemporaneous Ebola outbreak in the Kibaale district of Uganda. Reported numbers are subject to change.

2012: Ebola Hemorrhagic Fever Outbreak in Uganda

On July 28, 2012, the Uganda Ministry of Health reported an outbreak of Ebola Hemorrhagic Fever in the Kibaale District of Uganda. A total of 24 human cases (probable and confirmed only), 17 of which were fatal, were reported starting at the beginning of July. Laboratory tests of blood samples, conducted by the Uganda Virus Research Institute (UVRI) and the U.S. Centers for Disease Control and Prevention (CDC), confirmed Ebola virus in 11 patients, four of whom died. Reported numbers are subject to change.

On October 4, 2012, the Uganda Ministry of Health declared the outbreak ended.

2011: Ebola Hemorrhagic Fever Case in Uganda

On May 14, 2011, the Ugandan Ministry of Health informed the public that a patient with suspected Ebola Hemorrhagic fever died on May 6, 2011 in the Luwero district, Uganda. CDC-Uganda confirmed a positive Ebola virus test result from a blood sample taken from the patient. The quick diagnosis of Ebola virus was provided by the new CDC Viral Hemorrhagic Fever laboratory installed at the Uganda Viral Research Institute (UVRI).

Experts from the CDC have arrived in Entebbe, Uganda to actively assist the Ugandan Ministry of Health, local health officials, and international organizations in disease response. At the present time, there are no other known cases.

2008: Ebola-Reston virus detected in pigs in Philippines

On October 25, 2008, CDC received samples of pig tissues, sera and cell cultures from FADDL, the Foreign Animal Disease Diagnostic Laboratory on Plum Island, NY. The samples, originally collected from pig farms outside Manila, were initially tested at the Plum Island facility, which identified multiple swine pathogens, including Porcine Reproductive and Respiratory Syndrome (PRRS) virus and porcine circovirus type 2. Additional testing by molecular analysis also tentatively identified, for the first time in pigs, Ebola-Reston virus. Further testing of the samples at CDC’s Special Pathogens Branch and Infectious Disease Pathology Branch confirmed the presence of Ebola-Reston virus. Sequence analysis conducted at FADDL and CDC revealed that the virus is similar to the Ebola-Reston virus that infected macaques from the Philippines imported into the US for research in 1989, 1990 and 1996, and into Italy in 1992.

The clinical significance of Ebola-Reston in pigs is unknown, since many of the samples were obtained from pigs with dual PRRSV and Ebola-Reston virus infections. Epidemiologic investigations by Philippine authorities are continuing to look for evidence of human disease associated with infected pigs. Ebola-Reston virus is of unknown pathogenicity in humans. Recent studies of small numbers of Philippine slaughterhouse workers revealed antibodies to Ebola-Reston virus, with no clinical disease.

2007: Ebola Hemorrhagic Fever Outbreak in Uganda

On November 26, 2007, CDC received blood samples from the Ugandan Ministry of Health, taken from 20 of the 49 patients involved in an outbreak of an unknown illness in Bundibugyo district in western Uganda. Patients reported fever, enteritis, and bleeding. Of the 49, 14 have died. Genetic sequencing of a small segment of viral RNA from samples indicated the presence of a previously unknown strain of Ebola virus. At the invitation of the Ugandan Ministry of Health, CDC, WHO, MSF and other collaborators deployed field investigators to the affected region; additionally, a laboratory was set up in Entebbe at the Uganda Virus Research Institute (UVRI). As the outbreak neared conclusion in January 2008, the total number of suspected cases was 149, with 37 deaths.

2007: Ebola Hemorrhagic Fever Outbreak in the Democratic Republic of Congo (DRC)

On August 28, 2007, CDC was notified of cases of an unidentified disease in a remote area of Kasai Occidental Province in the Democratic Republic of Congo (DRC). Clinical samples were sent to the CDC Special Pathogens Branch laboratory for testing, as well as to the Centre International de Recherches Médicales de Franceville (CIRMF) laboratory in Gabon. Results obtained by both Real Time PCR and viral antigen assay were positive for infection with Ebola virus. The presence of other diseases in the same area of the country contributing to the outbreak cannot be ruled out. At the invitation of the DRC Ministry of Health, CDC, WHO, MSF and other collaborators have deployed field investigators to the region. The onset of the latest laboratory-confirmed case was on September 29, 2007. On October 1, 2007, the total of suspected cases was 249 with 183 deaths.

2004: Ebola Hemorrhagic Fever Outbreak in south Sudan

According to the World Health Organization (WHO), 20 cases, including 5 deaths, from Ebola hemorrhagic fever (EHF) have been reported from Yambio County in southern Sudan. EHF has been laboratory confirmed by both the Centers for Disease Control and Prevention (CDC) and the Kenya Medical Research Institute. CDC has confirmed that the virus is the Ebola-Sudan strain (incubation period: 2-21 days), one of three previously recognized Ebola virus strains known to cause human disease.

For related information regarding travel, please see the CDC Travelers’ Health Web site.

For information regarding the recent cases of Ebola hemorrhagic fever syndrome in south Sudan, please refer to the World Health Organization’s (WHO) Communicable Disease Surveillance and Response page.

2003: Ebola Hemorrhagic Fever Outbreak in The Republic of the Congo

For information regarding cases of Ebola hemorrhagic fever syndrome in The Republic of the Congo, please refer to the World Health Organization’s (WHO) Communicable Disease Surveillance and Response page.

2002: Ebola Hemorrhagic Fever Outbreak in Gabon and The Republic of the Congo

On May 6, 2002, the Gabonese Ministry of Health declared that the Ebola hemorrhagic fever outbreak in the Ogooué-Ivindo province had ended. CDC participated with the Gabonese and Congolese Ministries of Health, the World Health Organization (WHO), the International Center for Medical Research in Franceville, Gabon, and other partners in an international response to the outbreak in the Ogooué-Ivindo province of Gabon and in neighboring villages in the Republic of the Congo.

Ebola hemorrhagic fever is a severe, often fatal viral hemorrhagic disease. The virus can be transmitted by close contact with persons symptomatic with the disease. On the basis of extensive studies of previous outbreaks of Ebola hemorrhagic fever, general travelers in the area are unlikely to contract the disease. However, travelers are advised to take appropriate precautions to prevent infection. These precautions include avoiding direct contact with people who have serious disease and their bodily fluids.

For more information about the outbreak, please refer to the World Health Organization’s Communicable Disease Surveillance and Response Page.

For more information on the disease, please refer to the Ebola Hemorrhagic Fever Fact Sheet[PDF – 252KB].

For basic recommendations on VHF infection control, please refer to the CDC and WHO manual: Infection Control for Viral Hemorrhagic Fevers In the African Health Care Setting [PDF – 2MB].

2000-2001: Ebola Hemorrhagic Fever Outbreak in Uganda

On February 27, 2001, Uganda was declared officially to be free of Ebola hemorrhagic fever, following a 42-day period, twice the maximum incubation period, during which no new cases had been reported.

Between October 2000 and February 2001, CDC participated with the World Health Organization (WHO), the Ugandan Ministry of Health, Medecins Sans Frontieres (MSF), and other partners in an international response to the outbreak.

For more information about the outbreak in Uganda or about viral hemorrhagic fevers in general, please refer to the following:


Information for healthcare workers

(Click on the link that concerns you)



Protecting Healthcare Workers

U.S. Healthcare Settings

African Healthcare Settings

  • Infection Control for Viral Haemorrhagic Fevers in the African Health Care Setting
  • Infection Control Posters
    Includes French & Portuguese versions
  • Prevention

  • isolation-ward
    Because we still do not know exactly how people are infected with Ebola, few primary prevention measures have been established and no vaccine exists.

    When cases of the disease do appear, risk of transmission is increased within healthcare settings. Therefore, healthcare workers must be able to recognize a case of Ebola and be ready to use practical viral hemorrhagic fever isolation precautions or barrier nursing techniques. They should also have the capability to request diagnostic tests or prepare samples for shipping and testing elsewhere.

    Barrier nursing techniques include:

    • wearing of protective clothing (such as masks, gloves, gowns, and goggles)
    • using infection-control measures (such as complete equipment sterilization and routine use of disinfectant)
    • isolating patients with Ebola from contact with unprotected persons.

    The aim of all of these techniques is to avoid contact with the blood or secretions of an infected patient. If a patient with Ebola dies, direct contact with the body of the deceased patient should be avoided.

    CDC, in conjunction with the World Health Organization, has developed a set of guidelines to help prevent and control the spread of Ebola. Entitled Infection Control for Viral Haemorrhagic Fevers in the African Health Care Setting, the manual describes how to

    • recognize cases of viral hemorrhagic fever (such as Ebola)
    • prevent further transmission in healthcare setting by using locally available materials and minimal financial resources.

    If you must travel to an area with known Ebola cases, make sure to do the following:

    • Practice careful hygiene. Avoid contact with blood and body fluids.
    • Do not handle items that may have come in contact with an infected person’s blood or body fluids.
    • Avoid funeral or burial rituals that require handling the body of someone who has died from Ebola.
    • Avoid contact with bats and nonhuman primates or blood, fluids, and raw meat prepared from these animals.
    • Avoid hospitals where Ebola patients are being treated. The U.S. embassy or consulate is often able to provide advice on facilities.
    • After you return, monitor your health for 21 days and seek medical care immediately if you develop symptoms of Ebola.


Diagnosing Ebola HF in an individual who has been infected for only a few days is difficult, because the early symptoms, such as red eyes and a skin rash, are nonspecific to ebolavirus infection and are seen often in patients with more commonly occurring diseases.

However, if a person has the early symptoms of Ebola HF and there is reason to believe that Ebola HF should be considered, the patient should be isolated and public health professionals notified. Samples from the patient can then be collected and tested to confirm infection.

Laboratory tests used in diagnosis include:

Timeline of Infection Diagnostic tests available
Within a few days after symptoms begin
  • Antigen-capture enzyme-linked immunosorbent assay (ELISA) testing
  • Polymerase chain reaction (PCR)
  • Virus isolation
Later in disease course or after recovery
  • IgM and IgG antibodies
Retrospectively in deceased patients
  • Immunohistochemistry testing
  • PCR
  • Virus isolation


No specific vaccine or medicine (e.g., antiviral drug) has been proven to be effective against Ebola.

Symptoms of Ebola are treated as they appear. The following basic interventions, when used early, can increase the chances of survival.

  • Providing intravenous fluids and balancing electrolytes (body salts)
  • Maintaining oxygen status and blood pressure
  • Treating other infections if they occur

Timely treatment of Ebola HF is important but challenging because the disease is difficult to diagnose clinically in the early stages of infection. Because early symptoms, such as headache and fever, are nonspecific to ebolaviruses, cases of Ebola HF may be initially misdiagnosed.

However, if a person has the early symptoms of Ebola HF and there is reason to believe that Ebola HF should be considered, the patient should be isolated and public health professionals notified. Supportive therapy can continue with proper protective clothing until samples from the patient are tested to confirm infection.

Experimental treatments have been tested and proven effective in animal models but have not yet been used in humans.

Centre for Disease Control and Prevention

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