WHO – EBOLA VIRUS DISEASE (EVD)

Key facts

Ebola virus disease (EVD), formerly known as Ebola hemorrhagic fever, is a severe, often fatal illness

in humans.

EVD outbreaks have a case fatality rate of up to 90%.

EVD outbreaks occur primarily in remote villages in Central and West Africa, near tropical rainforests.

The virus is transmitted to people from wild animals and spreads in the human population through

human-to-human transmission.

Fruit bats of the Pteropodidae family are considered to be the natural host of the Ebola virus.

Severely ill patients require intensive supportive care. No licensed specific treatment or vaccine is

available for use in people or animals.

Ebola first appeared in 1976 in 2 simultaneous outbreaks, in Nzara, Sudan, and in Yambuku,

Democratic Republic of Congo. The latter was in a village situated near the Ebola River, from which

the disease takes its name.

Genus Ebolavirus is 1 of 3 members of the Filoviridae family (filovirus), along with genus

Marburgvirus and genus Cuevavirus. Genus Ebolavirus comprises 5 distinct species: 1. Bundibugyo ebolavirus (BDBV)

2. Zaire ebolavirus (EBOV)

3. Reston ebolavirus (RESTV)

4. Sudan ebolavirus (SUDV)

5. Taï Forest ebolavirus (TAFV).

BDBV, EBOV, and SUDV have been associated with large EVD outbreaks in Africa, whereas

RESTV and TAFV have not. The RESTV species, 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.

Transmission

Ebola is introduced into the human population through close contact with the blood, secretions, organs

or other bodily fluids of infected animals. In Africa, infection has been documented through the

handling of infected chimpanzees, gorillas, fruit bats, monkeys, forest antelope and porcupines found

ill or dead or in the rainforest.

Ebola then spreads in the community through human-to-human transmission, with infection resulting

from direct contact with the blood, secretions, organs or other bodily fluids of infected people, and

indirect contact with environments contaminated with such fluids. 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. This has occurred through close contact with patients when infection control precautions are not

strictly practiced.

Among workers in contact with monkeys or pigs infected with Reston ebolavirus, several infections

have been documented in people who were clinically asymptomatic. Thus, RESTV appears less

capable of causing disease in humans than other Ebola species.

However, the only available evidence available comes from healthy adult males. It would be

premature to extrapolate the health effects of the virus to all population groups, such as immuno-

compromised persons, persons with underlying medical conditions, pregnant women and children.

More studies of RESTV are needed before definitive conclusions can be drawn about the

pathogenicity and virulence of this virus in humans.

Signs and symptoms

EVD is a severe acute viral illness often characterized by the sudden onset of fever, intense weakness,

muscle pain, headache and sore throat. This is followed by vomiting, diarrhoea, rash, impaired kidney

and liver function, and in some cases, both internal and external bleeding. Laboratory findings include

low white blood cell and platelet counts and elevated liver enzymes.

People are infectious as long as their blood and secretions contain the virus. Ebola virus was isolated

from semen 61 days after onset of illness in a man who was infected in a laboratory.

The incubation period, that is, the time interval from infection with the virus to onset of symptoms, is

2 to 21 days.

Diagnosis

Other diseases that should be ruled out before a diagnosis of EVD can be made include: malaria,

typhoid fever, shigellosis, cholera, leptospirosis, plague, rickettsiosis, relapsing fever, meningitis,

hepatitis and other viral haemorrhagic fevers.

Ebola virus infections can be diagnosed definitively in a laboratory through several types of tests: antibody-capture enzyme-linked immunosorbent assay (ELISA)

antigen detection tests

serum neutralization test

reverse transcriptase polymerase chain reaction (RT-PCR) assay

electron microscopy

virus isolation by cell culture.

Samples from patients are an extreme biohazard risk; testing should be conducted under maximum

biological containment conditions.

Vaccine and treatment

No licensed vaccine for EVD is available. Several vaccines are being tested, but none are available for

clinical use.

Severely ill patients require intensive supportive care. Patients are frequently dehydrated and require

oral rehydration with solutions containing electrolytes or intravenous fluids.

No specific treatment is available. New drug therapies are being evaluated.

Ebola virus in animals

Although non-human primates have been a source of infection for humans, they are not thought to be

the reservoir but rather an accidental host like human beings. Since 1994, Ebola outbreaks from the

EBOV and TAFV species have been observed in chimpanzees and gorillas.

RESTV has caused severe EVD outbreaks in macaque monkeys (Macaca fascicularis) farmed in

Philippines and detected in monkeys imported into the USA in 1989, 1990 and 1996, and in monkeys

imported to Italy from Philippines in 1992.

Since 2008, RESTV viruses have been detected during several outbreaks of a deadly disease in pigs in

People’s Republic of China and Philippines. Asymptomatic infection in pigs has been reported and

experimental inoculations have shown that RESTV cannot cause disease in pigs.

Prevention and control

No animal vaccine against RESTV is available. Routine cleaning and disinfection of pig or monkey

farms (with sodium hypochlorite or other detergents) should be effective in inactivating the virus.

If an outbreak is suspected, the premises should be quarantined immediately. Culling of infected

animals, with close supervision of burial or incineration of carcasses, may be necessary to reduce the

risk of animal-to-human transmission. Restricting or banning the movement of animals from infected

farms to other areas can reduce the spread of the disease.

As RESTV outbreaks in pigs and monkeys have preceded human infections, the establishment of an

active animal health surveillance system to detect new cases is essential in providing early warning for

veterinary and human public health authorities.

New Species of Ebola Virus Discovered

November 24, 2008 Public Library of Science

Scientists report the discovery of a new species of Ebola virus, provisionally named Bundibugyo ebolavirus, in the open-access journal PLoS Pathogens. The virus, which was responsible for a hemorrhagic fever outbreak in western Uganda in 2007, has been characterized by a team of researchers from the Centers for Disease Control and Prevention in Atlanta, Georgia the Uganda Virus Research Institute; the Uganda Ministry of Health; and Columbia University. Ebola virus infection in humans causes severe disease for which there is presently no vaccine or other treatment. Case fatalities range historically between 53 and 90%. Therefore, research efforts into the Ebola virus genus and potential diagnostics are ongoing, with the discovery of Bundibugyo ebolavirus representing one of the latest pieces added to this puzzle. The new virus is genetically distinct from all other known Ebola virus species, differing by more than 30% at the genetic level. More traditional ELISA-based assays detected the new virus; however, the unique nature of this virus created initial challenges for traditional Ebola virus molecular diagnostic assays and genome sequencing approaches. To determine the genetic signature of this new Ebola virus species, scientists used a recently developed random-primed pyro-sequencing approach, quickly determining the genetic sequence of over 70% of the virus genome. Knowledge of this sequence then allowed for the rapid development of a sensitive molecular detection assay which was deployed to the field as part of the outbreak response. This draft sequence also allowed for easy completion of the whole genome sequence using a traditional primer walking approach and prompt confirmation that this virus represented a new Ebola virus species. Current worldwide efforts to design effective diagnostics, antivirals and vaccines will need to take into account the distinct nature of this new member of the Ebola virus genus.

Story Source: The above story is based on materials provided by Public Library of Science. Note: Materials may be

edited for content and length.

Journal Reference:

1. Towner et al. Newly Discovered Ebola Virus Associated with Hemorrhagic Fever Outbreak in Uganda. PLoS Pathog, 2008; 4(11): e1000212 DOI:10.1371/journal.ppat.1000212

Link: http://www.sciencedaily.com/releases/2008/11/081120202502.htm

Scientists Identify Protective Role for Antibodies in Ebola Vaccine Study

January 14, 2013

NIH/National Institute of Allergy and Infectious Diseases

Researchers at the National Institutes of Health (NIH) and Oregon Health & Science

University (OHSU) have found that an experimental vaccine elicits antibodies that can

protect nonhuman primates from Ebola virus infection. Ebola virus causes severe

hemorrhagic fever in humans and nonhuman primates, meaning that infection may lead

to shock, bleeding and multi-organ failure. According to the World Health Organization,

Ebola hemorrhagic fever has a fatality rate of up to 90 percent. There is no licensed

treatment or vaccine for Ebola virus infection.

Several research groups have developed experimental vaccine approaches that protect nonhuman primates from Ebola virus and the closely related Marburg virus. These approaches include vaccines based on DNA, recombinant adenovirus, virus-like particles, and human parainfluenza virus 3. But how these vaccine candidates confer protection is an area that is still being explored: Do they activate immune cells to kill the invading virus? Or do they elicit antibodies that block infection? In this study, scientists at NIH's National Institute of Allergy and Infectious Diseases and OHSU's Vaccine & Gene Therapy Institute built on earlier work with an experimental vaccine composed of an attenuated vesicular stomatitis virus carrying a gene that codes for an Ebola virus protein. They observed how cynomolgus macaques responded to a challenge of Ebola virus before and during treatment with the experimental vaccine and in conjunction with depleted levels of immune cells. Their results showed that important immune cells -- CD4+ T cells and CD8+ T cells -- had a minimal role in providing protection, while antibodies induced by the vaccine appeared to be critical to protecting the animals. The scientists say this finding will help improve future Ebola virus vaccine development. They plan to focus their studies on what level of antibody production is needed to establish protection from Ebola virus infection in humans.

Story Source:

The above story is based on materials provided by NIH/National Institute of Allergy and Infectious Diseases. Note: Materials may be edited for content and length.

Journal Reference:

1. A Marzi et al. Antibodies are necessary for rVSV/ZEBOV-GP mediated protection against lethal Ebola virus challenge in nonhuman primates.Proceedings of the National Academy of Sciences,

2013 DOI:10.1073/pnas.1209591110

Link: http://www.sciencedaily.com/releases/2013/01/130114161501.htm

Many in U.S. lack knowledge about Ebola, its transmission, poll finds

August 22, 2014

Harvard School of Public Health

Although the Centers for Disease and Prevention (CDC) reports no known cases of

Ebola transmission in the United States, a Harvard School of Public Health

(HSPH)/SSRS poll released shows that four in ten (39%) adults in the U.S. are

concerned that there will be a large outbreak in the U.S., and a quarter (26%) are

concerned that they or someone in their immediate family may get sick with Ebola over

the next year.

The nationally representative poll of 1,025 adults was conducted August 13-17, 2014 by researchers at HSPH and SSRS, an independent research company. The margin of error for total respondents is +/-3.6

percentage points at the 95% confidence level. Ebola hemorrhagic fever is a severe, often fatal disease in humans and nonhuman primates, such as

monkeys, gorillas and chimpanzees. Four countries have reported infections: Guinea, Liberia, Nigeria, and Sierra Leone. Officials report 1,350 have died as of August 21, 2014 and over 2,473 people have

been infected since March 2014. The HSPH/SSRS poll found people with less education are more likely to be concerned about an

outbreak in the U.S. (less than high school 50% vs. some college 36% vs. college grad or more 24%). People with less education are also more concerned they or their family will get sick with Ebola (less than

high school 37% vs. some college 22% vs. college grad or more 14%). Perhaps related, those with less education are also less likely to be following the news about the Ebola outbreak in West Africa closely

(total 63%; less than high school 57% and some college 62% vs. college grad or more 73%). Two-thirds of people (68%) surveyed believe Ebola spreads "easily" ("very easily" or "somewhat easily")

from those who are sick with it. This perception may contrast with CDC, World Health Organization (WHO), and other health experts who note that Ebola is not an airborne illness, and is transmitted through

direct contact with infected bodily fluids, infected objects, or infected animals. For more on how Ebola is transmitted:http://www.cdc.gov/vhf/ebola/transmission/index.html

A third of those polled (33%) believe there is "an effective medicine to treat people who have gotten sick with Ebola." According to the CDC and WHO, there is no proven anti-viral medicine, however, treating

symptoms -- such as maintaining fluids, oxygen levels, and blood pressure -- can increase the odds of survival. To date, the media reports two people infected with Ebola overseas have been treated in the

U.S. "Many people are concerned about a large scale outbreak of Ebola occurring in the U.S.," said Gillian

SteelFisher, PhD, deputy director of the Harvard Opinion Research Program and research scientist in the HSPH Department of Health Policy and Management. "As they report on events related to Ebola, the

media and public health officials need to better inform Americans of Ebola and how it is spread." Story Source: The above story is based on materials provided by Harvard School of Public Health. Note: Materials

may be edited for content and length.

Link: http://www.sciencedaily.com/releases/2014/08/140822094238.htm

Deceased

Dead

Porcupine An animal with many long, thin, shark spikes on its back.

Mourner A person who attends a funeral, especially as a relative or friend of the dead person

To draw conclusions

To sum something up

Jump to conclusions To make up your mind to quickly, usually without thinking

Precaution An action that is intended to prevent something dangerous or unpleasant from happening

Burial ceremony

The act of putting a dead body into a grave in the ground

Premise Something you suppose is true and that you use as a basis for development of an idea

Incineration

Get rid of something by burning it (syn.cremation)

Host Somebody or something who invites guests or provides facilities to some event as the main organizer

Relapsing Repeating

Remote Situated far away

Acute Severe or intense (e.g. about an illness or feeling)

Biohazard Severely dangerous

Assay Medical testing

Outbreak

Sudden start of something unpleasant (disease, violence, etc.)

Inoculation

Injection

Fever

High body temperature, fast heart beat

Virulence

Ability to harm or kill (about a disease)