The 2014 Ebola outbreak across Guinea, northern Liberia, and Sierra Leone has fuelled concern worldwide. According to the Centers for Disease Control and Prevention (CDC), with 9,427 laboratory confirmed cases of Ebola virus up to November 2014 and around 5,420 deaths from the epidemic, this has been the worst outbreak ever.
Medical News Today examines the effects of Ebola on the human body and the current concerns people may have about the virus.
Ebola virus disease (EVD), previous known as Ebola hemorrhagic fever (Ebola HF), is a serious, often fatal condition in humans and nonhuman primates such as monkeys, gorillas and chimpanzees. Ebola is one of several viral hemorrhagic fevers (VHF), caused by infection with a virus of the Filoviridae family, genus Ebolavirus.1-3
Ebola has a case fatality rate of up to 90% and is currently one of the world's most infectious diseases. The infection is transmitted by direct contact with the blood, body fluids and tissues of infected animals or people. Severely ill patients require intensive supportive care.4
When an Ebola infection occurs in humans, the virus can be spread in several ways to others. Above is a list of ways Ebola can and cannot be transmitted.
Contents of this article:
This Medical News Today information page will give you the essential details about Ebola. You will also see introductions at the end of some sections to any recent developments that have been covered by MNT's news stories. Also look out for links to information about related conditions.
Fast facts on Ebola
Here are some key points about Ebola. More detail and supporting information is in the main article.
- Ebola virus disease (EVD) is a serious, often fatal condition in humans and nonhuman primates.
- Ebola has a fatality rate of up to 90%.
- It is one of the world's most infectious diseases.
- Genus Ebolavirus is one of three members of the Filoviridae family (filovirus).
- It has been hypothesized by researchers that the virus is animal-borne.
- In an outbreak or isolated case among humans, the manner in which the virus is transmitted from the natural reservoir to a human is unclear.
- Ebola tends to spread quickly through families and friends as they are exposed to infectious secretions when caring for an ill individual.
- The time interval from infection with Ebola to the onset of symptoms is 2 to 21 days.
- EVD is often characterized by the abrupt onset of fever, intense weakness, muscle pain, headache and sore throat.
- There is currently no licensed vaccine available for Ebola.
- Several vaccines are being tested, but at this time none are available for clinical use.
What is Ebola?
The first cases of Ebola were reported simultaneously in 1976 in Yambuku and the surrounding area, near the Ebola River in Zaire, which is now the Democratic Republic of the Congo and in Nzara, Sudan. Since then, eruptions or asymptomatic cases of Ebola viruses in humans and animals have surfaced intermittently in the following locations due to outbreaks or laboratory contamination and accidents:5
The first cases of Ebola were reported in 1976 in Yambuku and the surrounding area, near the Ebola River in Zaire, which is now the Democratic Republic of the Congo.
- Zaire (Democratic Republic of the Congo - DRC)
- Sudan (South Sudan)
- Ivory Coast
- South Africa
- Sierra Leone.
Genus Ebolavirus is one of three members of the Filoviridae family (filovirus), along with genus Marburgvirus and genus Cuevavirus. Genus Ebolavirus comprises five distinct subspecies:1,2
- Bundibugyo Ebolavirus (BDBV)
- Zaire Ebolavirus (EBOV)
- Reston Ebolavirus (RESTV)
- Sudan Ebolavirus (SUDV)
- Taï Forest Ebolavirus (TAFV).
BDBV, EBOV, and SUDV have been connected with considerable EVD outbreaks in Africa, however RESTV and TAFV have not.
The RESTV subspecies found in Philippines and the People's Republic of China, can infect humans, but no illness or death in humans from this species has been reported to date.2 Among workers in contact with monkeys or pigs infected with RESTV, several infections have been documented in people who were clinically asymptomatic. Hence, RESTV appears less able to cause disease in humans than other Ebola species.
What causes Ebola?
Ebola is caused by the five viruses detailed above classified in the genus Ebolavirus, family Filoviridae. The natural reservoir of Ebolavirus has not yet been proven, for that reason, how the virus first appears in a human at the onset of an outbreak is unknown.6
It has been hypothesized by researchers that the virus is zoonotic (animal-borne), with the first patient developing the infection through contact with an infected animal.
Ebola is caused by the five viruses above classified in the genus Ebolavirus, family Filoviridae.
The theorized potential natural reservoirs of the Ebola virus are Fruit bats of the Pteropodidae family.2 In Africa, infection has been documented through the handling of the following infected animals found ill or dead or in the rainforest:
- Fruit bats
- Forest antelope
In an outbreak or isolated case among humans, the manner in which the virus is transmitted from the natural reservoir to a human is unclear. Person-to-person transmission is a method by which further infections occur after a human is infected.
Transmission of Ebola between humans can occur in several ways, including through:
- Direct contact through broken skin and mucus membranes with the blood, secretions, organs or other bodily fluids of infected people
- Indirect contact with environments contaminated with such fluids
- Exposure to objects (such as needles) that have been contaminated with infected secretions
- Burial ceremonies in which mourners have direct contact with the body of the deceased person can also play a role in the transmission of Ebola
- Men who have recovered from the disease can still transmit the virus through their semen for up to 7 weeks after recovery from illness
- Health care workers have frequently been infected while treating patients with suspected or confirmed EVD.
Ebola tends to spread quickly through families and friends as they are exposed to infectious secretions when caring for an ill individual. The virus can also spread quickly within health care settings for the same reason, highlighting the importance of wearing appropriate protective equipment, such as masks, gowns and gloves.7 Sterilization and disposal of needles and syringes thoroughly in hospitals is an important factor to prevent virus transmission continuing and amplifying an outbreak.
There is no evidence that Ebola can be spread via insect bites.8
Recent developments on Ebola causes from MNT news
An international research team has rapidly sequenced 99 Ebola virus genomes collected in the 2014 outbreak. The team, including members from the Broad Institute and Harvard University in the US and the Sierra Leone Ministry of Health and Sanitation, hopes the findings will help multidisciplinary, international efforts to understand and contain the unprecedented epidemic that is growing in West Africa.
A study, published in EMBO Molecular Medicine, suggests the outbreak of the Ebola virus disease occurring in West Africa may have originated from contact between humans and virus-infected bats. The insectivorous free-tailed bats in particular have been identified as plausible reservoir hosts.
After testing swabs and tissue samples from the bodies of deceased Ebola-infected monkeys, scientists determined the virus can stay alive for up to 7 days in a dead victim. They also found that non-infectious viral genetic material can remain for up to 70 days after death. The researchers report their findings in the journal Emerging Infectious Diseases.
New research finds that Ebola can survive in detectable concentrations in wastewater for 8 days - a finding that has implications for the disposal of contaminated liquid waste during epidemics and outbreaks.
A new study suggests that the Ebola virus is still detectable in semen samples from male survivors for at least 9 months after onset of symptoms.
On the next page we look at symptoms of Ebola, the risk factors and how Ebola is diagnosed. On the final page we discuss treatments for Ebola, methods of prevention and the spread of Ebola outbreaks.