Ebola haemorrhagic fever
- The Ebola virus causes severe viral haemorrhagic fever (VHF) outbreaks in humans.
- Viral haemorrhagic fever outbreaks have a case fatality rate of up to 90%.
- Ebola haemorrhagic fever 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.
- There is no treatment or vaccine available for either people or animals.
The Ebola virus can cause severe viral haemorrhagic fever (VHF) outbreaks in humans with a case fatality rate of up to 90%. Ebola first appeared in 1976 in two simultaneous outbreaks, in Nzara, Sudan, and in Yambuku, Democratic Republic of Congo (DRC). The latter was in a village situated near the Ebola River, from which the disease takes its name.
The Ebola virus is comprised of five distinct species: Bundibugyo, Ivory Coast, Reston, Sudan and Zaire.
Bundibugyo, Sudan and Zaire species have been associated with large Ebola haemorrhagic fever (EHF) outbreaks in Africa, while the Ivory Coast and Reston species have not. EHF is a febrile haemorrhagic illness which causes death in 25-90% of all cases. The Ebola Reston species, found in the Philippines, can infect humans, but no illness or death in humans has been reported to date.
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 dead or ill in the rainforest.
Later Ebola spreads in the community through human-to-human transmission, resulting from close contact with the blood, secretions, organs or other bodily fluids of infected people. Burial ceremonies where mourners have direct contact with the body of the deceased person can also play a role in the transmission of Ebola. Transmission via infected semen can occur up to seven weeks after clinical recovery.
Health-care workers have frequently been infected while treating Ebola patients. This has occurred through close contact without the use of correct infection control precautions and adequate barrier nursing procedures. For example, health-care workers not wearing gloves and/or masks and/or goggles may be exposed to direct contact with infected patients' blood and are at risk.
Among workers in contact with monkeys or pigs infected with Ebola Reston, several human infections have been documented and were clinically asymptomatic. Thus, the Ebola Reston virus appears to be less capable of causing disease in humans than the other Ebola species. However, the evidence available relates only to healthy adult males. It would be premature to conclude the health effects of the virus on all population groups, such as immuno-compromised persons, persons with underlying medical conditions, pregnant women and children. More studies of Ebola Reston virus are needed before definitive conclusions can be made about the pathogenicity and virulence of this virus in humans.
Signs and symptoms
EHF 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 show low counts of white blood cells and platelets as well as elevated liver enzymes.
People are infectious as long as their blood and secretions contain the virus. Ebola virus was isolated from seminal fluid up to the 61st day after the onset of illness in a laboratory acquired case.
The incubation period (interval from infection to onset of symptoms) varies between 2 to 21 days.
During EHF outbreaks, the case-fatality rate has varied from outbreak to outbreak between 25% and 90%.
Differential diagnoses include, malaria, typhoid fever, shigellosis, cholera, leptospirosis, plague, rickettsiosis, relapsing fever, meningitis, hepatitis and other VHFs.
Ebola virus infections can only be diagnosed definitively in the laboratory by a number of different tests:
- enzyme-linked immunosorbent assay (ELISA)
- antigen detection tests
- serum neutralization test
- reverse transcriptase polymerase chain reaction (RT-PCR) assay
- virus isolation by cell culture.
Tests on samples from patients are an extreme biohazard risk and should only be conducted under maximum biological containment conditions.
Treatment and vaccine
Severe cases require intensive supportive care. Patients are frequently dehydrated and in need of intravenous fluids or oral rehydration with solutions containing electrolytes.
No specific treatment or vaccine is yet available for EHF. New drug therapies have shown promising results in laboratory studies and are currently being evaluated. Several vaccines are being tested but it could be several years before any are available.
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 Zaire and Ivory Coast species have been found in chimpanzees and gorillas.
Ebola Reston has caused severe VHF outbreaks in macaque monkeys (Macaca fascicularis) farmed in the Philippines and in imported monkeys in 1989, 1990 and 1996 to the USA and in 1992 in monkeys imported to Italy from the Philippines.
Since 2008, Ebola Reston viruses were detected during several outbreaks of a deadly disease in pigs. Asymptomatic infection in pigs has been reported and experimental inoculations tend to demonstrate that Ebola Reston cannot cause a disease in pigs.
Controlling Ebola Reston in domestic animals
There is no animal vaccine available against Ebola Reston. Routine cleaning and disinfection of pig or monkey farms (with sodium hypochlorite or other detergents) is expected to 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 Ebola Reston 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 of Ebola infection and the protective measures individuals can take is the only way to reduce human infection and death.
In Africa, during EHF 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. Their 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 sick relatives in hospital, as well as after taking care of ill 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 deceased. People who have died from Ebola should be promptly and safely buried.
- Precautionary measures are needed in Africa to avoid that pig farms infected through contact with fruit bats amplify the virus and cause EHF outbreaks.
For Ebola Reston, 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 or when slaughtering animals. In the regions where Ebola Reston has been reported/detected in pigs, all animal products (blood, meat and milk) should be thoroughly cooked before eating.
Controlling infection in health-care settings
Human-to-human transmission of the Ebola virus is primarily associated with direct contact with blood and body fluids. Transmission to healthcare workers has been reported when appropriate infection control measures have not been observed.
Health-care workers caring for patients with suspected or confirmed Ebola virus should apply infection control precautions to avoid any exposure to the patient’s blood and body fluids and/or direct unprotected contact with the possibly contaminated environment. Therefore the provision of health care for suspected or confirmed Ebola patients requires specific control measures and the reinforcement of standard precautions, particularly basic hand hygiene, the use of personal protective equipment, safe injections practices and safe burial practices.
Laboratory workers are also at risk. Samples taken from suspected human and animal Ebola cases for diagnosis should be handled by trained staff and processed in suitably-equipped laboratories.
WHO has been involved in all past Ebola outbreaks by providing expertise and documentation to support disease investigation and control.
Recommendations for infection control while providing care to patients with suspected or confirmed Ebola haemorrhagic fever is provided in the: Interim infection control recommendations for care of patients with suspected or confirmed Filovirus (Ebola, Marburg) haemorrhagic fever, March 2008.
WHO has created an aide–memoire on standard precautions in health care. Standard precautions are meant to reduce the risk of transmission of bloodborne and other pathogens. If universally applied the precautions would help prevent most transmission through exposure to blood and body fluids. Standard precautions are recommended in the care and treatment of all patients regardless of their perceived or confirmed infectious status. They include the basic level of infection control and include hand hygiene, use of personal protective equipment to avoid direct contact with blood and body fluids, prevention of needle stick and injuries from other sharp instruments, and a set of environmental controls.
Table: Chronology of major Ebola haemorrhagic fever outbreaks (as of May 2012)
|Year||Country||Virus subtype||Cases||Deaths||Case fatality|
|2008||Democratic Republic of Congo||Ebola Zaire||32||14||44%|
|2007||Democratic Republic of Congo||Ebola Zaire||264||187||71%|
|1996||South Africa (ex-Gabon)||Ebola Zaire||1||1||100%|
|1995||Democratic Republic of Congo||Ebola Zaire||315||254||81%|
|1994||Cote d'Ivoire||Ebola Ivory Coast||1||0||0%|
|1977||Democratic Republic of Congo||Ebola Zaire||1||1||100%|
|1976||Democratic Republic of Congo||Ebola Zaire||318||280||88%|