EVD, formerly known as haemorrhagic fever, is a severe and often fatal disease caused by a group of Viruses called the Ebolaviruses.

According to the Centers for Disease Control and Prevention, the largest outbreak of the disease to date took place between the years of 2014 and 2016 in West Africa. There were limited cases in Italy, Nigeria, Spain, and the U.K.

According to the World Health Organization, the Marburg virus is a member of the same family of Viruses as the Ebola virus. There were two major outbreaks in Germany and Serbia in 1967, which were linked to monkeys imported from Africa. Since then, there have been sporadic cases, mostly in Africa, where the disease hadn't been seen before.

The deadliest Viruses in History.


When was Ebola discovered?

According to the CDC, the first case of the disease was discovered in 1976 in the areas that are now South Sudan and the Democratic Republic of theCongo. The outbreak in the Republic of Zare took place in a village close to the river.

Although initially thought to be part of the same large outbreak, the two 1976 outbreak were caused by genetically distinct viruses that spread through each locale. After the areas where they were found, they were named after.

What are Ebola viruses?

According to the CDC, the most common causes of EVD in humans and nonhuman primate are the viruses in the family Filoviruses.

Severe disease in humans has been caused by four of the six species of Ebolaviruses. These are included.

  • 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)

The Bombali virus is one of the two remaining species of the ebolaviruses. The first has been reported to cause illness in nonhuman primate and pigs, but it's not yet known if the second causes illness in humans or animals.

According to a report in the journal Nature Microbiology, the Bombali virus was discovered by scientists while they were analyzing oral and rectal samples from free-tailed bats.

There are at least six different species of the Ebola virus in bats.

Where did Ebola viruses come from?

photo of several brown fruit bats hanging upside down from a branch

Fruit bats are thought to be the reservoir for Ebola viruses. (Image credit: Michele D'Amico supersky77 via Getty Images)

The term "spillover event" refers to the spread of the virus from animals to people. Chimpanzees, gorillas, monkeys, forest antelope, porcupines and bats are some of the animals that can carry the disease, according to the World Health Organization.

According to the CDC, current evidence shows that African fruit bats serve as the natural "reservoir" for the viruses. The animals are likely to carry the viruses without getting sick and act as the primary vessels for the viruses. The viruses can be spread from bats to other animals.

Scientists don't know which fruit bat is the main host of the virus. The free-tailed bats of Sierra Leone have been found to be carrying the virus.

How does Ebola spread?

According to the WHO, when people come into close contact with the blood, secretions, organs or other bodily fluids of an animal that's been bitten by the virus, it can jump from there to humans.

The blood, secretions, organs, and other body fluids of a healthy person must come into contact with a broken skin or the mucus of a sick person in order for the virus to be transmitted. It is possible that the fluids come from the sick person or from the patient.

According to an assessment by the World Health Organization, blood, feces and vomit are the easiest ways to transmit the disease. According to the CDC, the virus can be spread through urine, saliva, sweat, breast milk, amniotic fluid and semen.

Even if a patient no longer has symptoms of EVD, the CDC warns that the virus can still be found in certain fluids. The WHO recommends that EVD survivors with penises refrain from sex or use condoms until their semen has been tested twice for the disease or until 12 months after their initial symptoms have passed.

The CDC states that there is no evidence that the disease can be spread through sex. Even after they've recovered, the virus can still be found in the amniotic fluid of people who became pregnant and in the breast milk of people who became pregnant.

A person can't contract the virus from breathing the same air as someone who's been exposed. If a person sneezes on another person and the mucus from that sneeze comes into contact with their eyes, nose or mouth, there is a chance that they will get an infectious disease. This has not been documented by WHO.

What are the symptoms of Ebola?

Health care workers put on protective gear before entering an Ebola treatment unit in Liberia during the 2014 Ebola outbreak..

Health care workers put on protective gear before entering an Ebola treatment unit in Liberia during the 2014 Ebola outbreak. (Image credit: CDC/Sally Ezra/Athalia Christie (Public Domain))

According to the CDC, symptoms of EVD can appear two to 21 days after exposure.

The symptoms of the disease are not specific in the beginning. The Centers for Disease Control and Prevention states that the early stages of an infectious disease may look similar to flu, Malaria, or typhoid.

The symptoms that the patient will experience are listed by the CDC.

  • 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; bleeding can be both internal and external

The CDC says that patients progress from the "dry" symptoms to the "wet" symptoms over time. Usually hemorrhagic syndrome occurs in the late stages of the disease. According to a research assistant professor at the University of Washington, 70% to 50% of patients are affected by the Ebola virus.

There are other symptoms that occur in advanced stages of EVD. In the last stages of the disease, people may develop red eyes.

Medical professionals use a number of tests to diagnose EVD because the symptoms of the disease are similar to other diseases. Common tests are listed by the WHO.

  • Virus isolation by cell culture
  • Antibody-capture enzyme-linked immunosorbent assay (ELISA)
  • Serum neutralization test
  • Antigen-capture detection tests
  • Electron microscopy
  • Reverse transcriptase polymerase chain reaction (RT-PCR) assay

How deadly is Ebola?

EVD can be deadly. According to the WHO, the case fatality rates have ranged from 25% to 90% in the past.

According to the Centers for Disease Control and Prevention (opens in new tab), 11,308 deaths were reported out of 28,610 cases, meaning 39% of them were fatal.

The human body is able to fight off infections. Jonathan Lai, associate professor of biochemistry at Albert Einstein College of Medicine in New York, said that the antibodies stop the flu from spreading and help clear it from the body. He told Live Science that the problem with the virus is that it can easily overcome the immune system.

How to prevent Ebola transmission

When living in or traveling to a region where the EVD is present, the CDC has some tips to follow.

  • 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 with EVD.
  • 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.

Are there vaccines for Ebola?

close up of a gloved nurse injecting an ebola vaccine into a sitting patient's arm

Two Ebola vaccines are now in use. (Image credit: ISSOUF SANOGO / Contributor via Getty Images)

Two vaccines have been developed for the prevention of EVD.

The European Medicines Agency approved Ervebo in November and the FDA approved it in December. Since then, it has been approved for use in a number of countries.

The single-dose vaccine is approved for use in individuals 18 years of age and older, who are not pregnant or breastfeeding, and has been found to be highly safe and against the most deadly form of the disease, the ebolaviruses.

The first dose of the vaccine is called Zabdeno and the second one is called Mvabea. According to the WHO, multiple clinical studies have shown that the two-dose vaccine is safe and effective, but the exact level of protection is unknown.

The European Medicines Agency recommended in 2020 that Zabdeno-and-Mvabea be used in individuals as young as 1 year old. According to the CDC, this vaccine has not been approved for routine use by the FDA, but it has been used for research purposes.

How is Ebola treated?

The FDA approved two treatments for EVD in 2020. One of the antibodies in Inmazeb is lab-made and protects against the virus. The second treatment has the same effect as the first one.

The two treatments were shown to increase patients' chance of survival in a clinical trial. Neither treatment has been evaluated for effectiveness against other viruses.

In the event that Inmazeb is unavailable, supportive care measures can help patients. Such care is included.

  • 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.

What recovery from Ebola looks like

EVD survivors face long- lasting medical problems and other changes in their bodies.

The testicles, the inside of the eye, and the central nervous system are some of the areas where virtual particles can persist. The CDC says "whether the virus is present in these body parts and for how long varies by survivors."

A survivor may have been the cause of the new outbreak.

The viruses can be found in semen, amniotic fluid, and breast milk of people who have been exposed while breastfeeding. In the context of EVD, the WHO gives specific guidance for managing pregnancies and breastfeeding.

According to the CDC, EVD survivors often report headaches, muscle and joint pain, stomach pain, and eye and vision problems. There are other long-term consequences of the infections.

  • 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
  • Impotence
  • Decreased or lost interest in sex
  • Changes in menstruation
  • Difficulty falling or remaining asleep
  • Depression, anxiety, and post-traumatic stress disorder (PTSD)

A report in The New England Journal of Medicine stated that one survivor had a change in eye color due to inflammation and high blood pressure. The fluid in the eye was found to contain the virus, but it was not thought to be infectious.

According to the CDC, EVD survivors can develop an immunity to the virus for at least a decade. It's not known if people who recover are immune for the rest of their lives or if they'll be exposed to a different type of virus.

Additional resources

You can learn about the FDA-approved treatments for the disease withSciShow. Bats carry a lot of dangerous Viruses in Science Magazine. In the new tab, you can learn about the strategies used to control and prevent the spread of the disease.

The article is not meant to give medical advice.