THE DEADLY VIRUS EBOLA

Key facts

Ebola virus disease (EVD), formerly known as

Ebola haemorrhagic 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 (through broken

skin or mucous membranes) 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.

Natural host of Ebola virus

In Africa, fruit bats, particularly species of the

genera Hypsignathus monstrosus, Epomops

franqueti and Myonycteris torquata , are

considered possible natural hosts for Ebola virus.

As a result, the geographic distribution of

Ebolaviruses may overlap with the range of the

fruit bats.

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

Controlling Reston ebolavirus in domestic

animals

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.

Reducing the risk of Ebola infection in people

In the absence of effective treatment and a

human vaccine, raising awareness of the risk

factors for Ebola infection and the protective

measures individuals can take is the only way to

reduce human infection and death.

In Africa, during EVD outbreaks, educational

public health messages for risk reduction should

focus on several factors:

Reducing the risk of wildlife-to-human

transmission from contact with infected fruit

bats or monkeys/apes and the consumption

of their raw meat. Animals should be handled

with gloves and other appropriate protective

clothing. Animal products (blood and meat)

should be thoroughly cooked before

consumption.

Reducing the risk of human-to-human

transmission in the community arising from

direct or close contact with infected patients,

particularly with their bodily fluids. Close

physical contact with Ebola patients should

be avoided. Gloves and appropriate personal

protective equipment should be worn when

taking care of ill patients at home. Regular

hand washing is required after visiting

patients in hospital, as well as after taking

care of patients at home.

Communities affected by Ebola should inform

the population about the nature of the disease

and about outbreak containment measures,

including burial of the dead. People who have

died from Ebola should be promptly and

safely buried.

Pig farms in Africa can play a role in the

amplification of infection because of the presence

of fruit bats on these farms. Appropriate

biosecurity measures should be in place to limit

transmission. For RESTV, educational public

health messages should focus on reducing the

risk of pig-to-human transmission as a result of

unsafe animal husbandry and slaughtering

practices, and unsafe consumption of fresh

blood, raw milk or animal tissue. Gloves and

other appropriate protective clothing should be

worn when handling sick animals or their tissues

and when slaughtering animals.