Ebola Virus Disease (EVD) formerly known as Ebola haemorrhagic fever, is a rare and deadly disease in people and nonhuman primates. The Ebola virus causes an acute, serious illness which is often fatal if untreated. Early in the disease and often causes internal and external hemorrhage (bleeding) as the disease progresses.

Ebola hemorrhagic fever is one of the most life-threatening viral infections; the mortality rate (death rate) may be very high during outbreaks (reports of outbreaks range from about 25%-100% of people infected, depending on the Ebola strain). Because most outbreaks occur in areas where high-level intensive care supportive public health services are not available, survival rates are difficult to translate to potential outbreaks in Ebola-affected areas with more resources.

EVD first appeared in 1976 in 2 simultaneous outbreaks, one in what is now Nzara, South Sudan, and the other in Yambuku, DRC. The latter occurred in a village near the Ebola River, from which the disease takes its name. 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 Ebola virus.

What is Ebola Virus Disease

The virus family Filoviridae includes three genera: Cuevavirus, Marburgvirus, and Ebolavirus.

Ebola Virus Disease (EVD) is a rare and deadly disease most commonly affecting people and nonhuman primates (monkeys, gorillas, and chimpanzees). It is caused by an infection with a group of viruses within the genus Ebolavirus.

Within the genus Ebolavirus, six species have been identified:

  • 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)

The virus causing the current outbreak in DRC and the 2014–2016 West African outbreak belongs to the Zaire ebolavirus species.

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 Bombali virus, which was recently identified in bats, causes disease in either animals or people.

Ebola virus spreads to people through direct contact with bodily fluids of a person who is sick with or has died from EVD. This can occur when a person touches the infected body fluids (or objects that are contaminated with them), and the virus gets in through broken skin or mucous membranes in the eyes, nose, or mouth. The virus can also spread to people through direct contact with the blood, body fluids and tissues of infected fruit bats or primates. People can get the virus through sexual contact as well.

Ebola survivors may experience difficult side effects after their recovery, such as tiredness, muscle aches, eye and vision problems and stomach pain. Survivors may also experience stigma as they re-enter their communities.

History of Ebola Virus Disease

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.

Scientists do not know where Ebola virus comes from, based on the nature of similar viruses, they believe the virus is animal-borne, with bats being the most likely source. The bats carrying the virus can transmit it to other animals, like apes, monkeys, duikers and humans.

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.

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. 1 The most recent Ebola virus to be detected, Bombali virus, was identified in samples from bats collected in Sierra Leone.

History of Ebola Outbreaks

Since its discovery in 1976, the majority of cases and outbreaks of Ebola Virus Disease have occurred in Africa.

The 2014–2016 outbreak in West Africa was the largest Ebola outbreak since the virus was first discovered in 1976. The outbreak started in Guinea and then moved across land borders to Sierra Leone and Liberia. The current 2018-2019 outbreak in eastern DRC is highly complex, with insecurity adversely affecting public health response activities.

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.

There is no approved vaccine or treatment for EVD. Research on EVD focuses on finding the virus’ natural host, developing vaccines to protect at-risk populations, and discovering therapies to improve treatment of the disease.

People diagnosed with Ebola or Marburg virus receive supportive care and treatment for complications. Scientists are coming closer to developing vaccines for these deadly diseases.

Prognosis of Ebola hemorrhagic fever

The prognosis of Ebola hemorrhagic fever is often poor; the death rate of this disease ranges from 25%-100%, and those who survive may experience the complications listed above. However, early diagnosis and treatment of Ebola may greatly increase the patient’s chance for survival. Unfortunately, this disease has been mainly located in countries where medical care is often difficult to obtain, especially in rural areas of Africa. Statistics available on the ongoing 2014-2016 outbreak of Ebola are summarized below:

  • Total suspected, probable, and confirmed infections worldwide equal 28,616, and total deaths equal 11,310 for a death rate or death toll of approximately 41%. An occasional new infection (at a low level) and deaths of current patients are unlikely to change these numbers substantially as the epidemic outbreak has ended according to the CDC. Fortunately, this epidemic of 2014-2016 did not become a pandemic but did show how rapidly a relatively rare disease like Ebola can rapidly infect a large number of individuals in this modern-day society.



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