History of EBOLA Virus

In 1976, Ebola, which is named after the Ebola River in Zaire first emerged in Sudan and Zaire. The first outbreak of Ebola called Ebola-Sudan infected over 284 people, with a mortality rate of 53%. A few months later, the second Ebola virus emerged from Yambuku, Zaire knew as Ebola-Zaire (EBOZ). EBOZ, with the highest mortality rate of any of the Ebola viruses (88%), infected 318 people. Despite the tremendous effort of experienced and dedicated researchers, Ebola’s natural reservoir was never identified. The third strain of Ebola, Ebola Reston (EBOR), was first identified in 1989 when infected monkeys were imported into Reston, Virginia, from Mindanao in the Philippines. Fortunately, the few people who were infected with EBOR (seroconverted) never developed Ebola hemorrhagic fever (EHF). The last known strain of Ebola, Ebola Côte d’Ivoire (EBO-CI) was discovered in 1994 when a female ethologist performing a necropsy on a dead chimpanzee from the Tai Forest, Côte d’Ivoire, accidentally infected herself during the necropsy. 

What is EBOLA Virus Disease?

Ebola Virus Disease (EVD) is a rare and deadly disease in people and nonhuman primates. The viruses that cause EVD are located mainly in sub-Saharan Africa. People can get EVD through direct contact with an infected animal (bat or nonhuman primate) or a sick or dead person infected with the Ebola virus. Ebola is caused by viruses in the Ebolavirus and Filoviridae family. Ebola is considered a zoonosis, meaning that the virus is present in animals and is transmitted to humans.

Causes of EBOLA Virus Disease

There is no approved vaccine or treatment for EVD. Research on EVD focuses on finding the virus’s natural host, developing vaccines to protect at-risk populations, and discovering therapies to improve treatment of the disease. In Africa, people have developed Ebola after handling infected animals found ill or dead, including chimpanzees, gorillas, fruit bats, monkeys, forest antelope, and porcupines. Person-to-person transmission occurs after someone infected with the Ebola virus becomes symptomatic. As it can take between 2 and 21 days for symptoms to develop, a person with Ebola may have been in contact with hundreds of people, which is why an outbreak can be hard to control and may spread rapidly.

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) are known to cause disease in people. Reston virus is known to cause disease in nonhuman primates and pigs, but not in people. It is unknown if the Bombali virus, which was recently identified in bats, causes disease in either animals or people.

How does it spread?

Scientists think people are initially infected with the Ebola virus through contact with an infected animal, such as a fruit bat or nonhuman primates. 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, and semen) of a person who is sick with or has died from Ebola Virus Disease (EVD)
  • Objects (such as needles and syringes) contaminated with body fluids from a person sick with EVD or the body of a person who 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 bodily 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 contacts with vaginal fluids from a woman who has had Ebola.

When someone gets infected with Ebola, they will not show signs or symptoms of illness right away. The Ebola virus CANNOT spread to others until a person develops signs or symptoms of EVD. After a person infected with Ebola develops symptoms of illness, they can spread Ebola to others.

Additionally, the Ebola virus usually is not transmitted by food. However, in certain parts of the world, the Ebola virus may spread through the handling and consumption of bushmeat (wild animals hunted for food). There is also no evidence that mosquitoes or other insects can transmit Ebola virus.

Symptoms of EBOLA Virus Disease

Symptoms of Ebola Virus Disease (EVD) include:

  • Fever
  • Severe headache
  • Muscle pain
  • Weakness
  • Fatigue
  • Diarrhea
  • Vomiting
  • Abdominal (stomach) pain
  • Unexplained hemorrhage (bleeding or bruising)

Symptoms may appear anywhere from 2 to 21 days after contact with the virus, with an average of 8 to 10 days. Many common illnesses can have these same symptoms, including influenza (flu) or malaria.

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 (molecules that are made by the immune system to label invading pathogens for destruction) that can be detected in the blood up to 10 years after recovery.

 

Diagnosis of Ebola Virus Disease

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 the Ebola virus infection 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. 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 primates (apes or monkeys)
  • semen from a man who has recovered from EVD

If a person shows early 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, most notably fever. It may take up to three days after symptoms start for the virus to reach detectable levels. A positive laboratory test means that the Ebola infection is confirmed. Public health authorities will conduct a public health investigation, including tracing of all possibly exposed contacts.

Treatment of Ebola Virus Disease

Symptoms of Ebola Virus Disease (EVD) are treated as they appear. When used early, basic interventions can significantly improve the chances of survival. These include:

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

Recovery from EVD depends on good supportive care and the patient’s immune response. Those who do recover develop antibodies that can last 10 years, possibly longer. 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.

There is currently no antiviral drug licensed in order to treat EVD in people. Drugs that are being developed to treat EVD work by stopping the virus from making copies of itself.

Blood transfusions from survivors and mechanical filtering of blood from patients are also being explored as possible treatments for EVD.

Prevention of Ebola Virus Disease

Ebola virus disease (EVD) is a very rare disease that has only occurred because of cases that were acquired in other countries, eventually followed by the human to human transmission. EVD is more common in some parts of sub-Saharan Africa, with occasional outbreaks occurring in people. In these areas, the Ebola virus is believed to circulate at low rates in certain animal populations (enzootic). Occasionally people become sick with Ebola after coming into contact with these infected animals, which can then lead to Ebola outbreaks where the virus spreads between people.

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

While in an area affected by Ebola, it is important to avoid the following:

  • Contact with blood and body fluids (such as urine, feces, saliva, sweat, vomit, breast milk, semen, and vaginal fluids).
  • Items that may have come in contact with an infected person’s blood or body fluids (such as clothes, bedding, needles, and medical equipment).
  • Funeral or burial rituals that require handling the body of someone who died from EVD.
  • Contact with bats and nonhuman primates or blood, fluids and raw meat prepared from these animals (bushmeat) or meat from an unknown source.
  • Contact with semen from a man who had EVD until you know the virus is gone from the semen.

These same prevention methods apply when living in or traveling to an area affected by an Ebola outbreak. After returning from an area affected by Ebola, monitor your health for 21 days and seek medical care immediately if you develop symptoms of EVD.

 

There is currently no vaccine licensed to protect people from the Ebola virus. An experimental vaccine called rVSV-ZEBOV was found to be highly protective against the virus in a trial conducted by the World Health Organization (WHO) and other international partners in Guinea in 2015. Around 300,000 doses have been committed for an emergency use stockpile under the appropriate regulatory mechanism (Investigational New Drug application [IND] or Emergency Use Authorization [EUA]) in the event an outbreak occurs before FDA approval is received. Scientists continue to study the safety of this vaccine in populations such as children and people with HIV.

Another Ebola vaccine candidate, the recombinant adenovirus type-5 Ebola vaccine, was evaluated in a phase 2 trial in Sierra Leone in 2015. An immune response was stimulated by this vaccine within 28 days of vaccination, the response decreased over six months after injection. Research on this vaccine is ongoing.

 

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