Ebola is one of the haemorrhagic fevers, a group of viral diseases that can cause haemorrhaging (bleeding) in most cases, and can be fatal.
Haemorrhagic fevers are most common in tropical areas. Ebola is endemic to (occurs naturally in) sub-Saharan Africa.
Most haemorrhagic fever viruses, including Ebola, have no known cure and can only be treated with supportive care.
Control of insects (“vectors”) that are known to carry some of these viruses, and personal protection measures, can help prevent haemorrhagic fevers.
Ebola haemorrhagic fever, commonly known as "Ebola", is a disease that causes severe bleeding abnormalities, and is often fatal.
Ebola belongs to a group of diseases called haemorrhagic fevers, so-called because they have the potential to cause haemorrhaging (bleeding) from internal organs and body orifices in most cases. Ebola outbreaks have occurred in Zaire, Sudan, Gabon, and most recently in Uganda.
Other examples of haemorrhagic fevers include Lassa fever, yellow fever, Marburg fever, dengue fever and Rift Valley fever. Congo-Crimean haemorrhagic fever is the most common viral haemorrhagic fever in South Africa, with several cases confirmed every year.
Causes and risk factors
Haemorrhagic fevers are caused by viruses that occur in different regions of the world, but tend to occur most commonly in tropical areas.
These viruses persist in nature in certain animal populations, which act as disease "reservoirs". Individuals in these animal populations become infected with the virus, but not fatally. The virus can be transmitted directly from a reservoir animal to a person or via an intermediary “vector”, such as a mosquito. For some of the viruses that cause haemorrhagic fevers, like Ebola, the reservoir hosts have still to be identified. Human-to-human transmission in health care settings or through sexual contact can also occur.
Haemorrhagic fevers are generally endemic (associated with a specific area and population). If many people live in an endemic area, the number of cases may increase rapidly. Dengue fever, for example, affects about 100 million people annually, many of whom live in densely populated southeast Asia. Some haemorrhagic fevers are rare, because people seldom come into contact with the virus. Marburg fever, for example, has affected fewer than 40 people since its discovery in 1967.
Ebola belongs to the virus family Filoviridae, which also includes the Marburg virus. Ebola is endemic to Africa, particularly the Congo and Sudan. Despite an intensive search, the natural reservoirs of the filoviruses, and the exact mode of transmission of Ebola into human population, are unknown. Available evidence and comparisons drawn with similar viruses suggest that Ebola is animal-borne, and is maintained in an animal host native to Africa. However, once an Ebola epidemic has started, the transmission of the virus between humans is clearly due to contamination of individuals with body fluid and through contact with objects, such as needles, contaminated by infected secretions.
It may be possible for Ebola to spread via airborne particles. However, this has only been demonstrated under laboratory conditions, with a particular strain of Ebola called Ebola Reston that primarily infects non-human primates and has never been documented among humans in a real-world context.
Symptoms and signs
The onset of haemorrhagic fevers may be sudden or gradual, and may progress to a mild illness or a serious, even fatal disease. All haemohrragic fevers have the potential to cause haemorrhaging, but this does not occur in all cases. Haemorrhaging may result from the destruction of blood coagulating factors or from increased permeability of body tissues. Severity of bleeding ranges from petechiae (pinpoint haemorrhages beneath the skin surface) to profuse bleeding from orifices.
The incubation period (time between infection and appearance of symptoms) for Ebola is thought to be from three to eight days. Symptoms appear suddenly and may include:
Malaise (feeling of discomfort)
Backache and other muscle aches
Conjunctivitis (eye inflammation)
Raised rash over the entire body
Reddening of roof of the mouth
Genital swelling (labia or scrotum)
Depression, apathy and disorientation
Increased sense of pain in the skin
Bleeding from the gastrointestinal tract (from mouth and rectum), and other orifices such as the eyes, ears, nose and vagina. Other bleeding symptoms include petechiae and oozing from injection sites.
To positively identify a specific haemorrhagic disease, doctors will look for evidence of the virus in the bloodstream, such as certain antigens and antibodies (proteins that indicate the presence of an invasive agent), or will attempt to isolate the virus itself. Disruptions in the normal levels of bloodstream components may help determine the presence of some haemorrhagic fevers.
Diagnosing Ebola in someone who has been infected for only a few days is difficult because early symptoms, such as eye inflammation and skin rash, resemble symptoms of several other more common conditions. If Ebola is suspected, laboratory tests should be done promptly. Only one laboratory in South Africa (the National Institute for Communicable Diseases) is equipped to perform tests for Ebola. This laboratory serves as a World Health Organisation reference centre for haemorrhagic diseases and also provides this diagnostic test service to many other African countries.
Lassa fever and possibly some of the other haemorrhagic fevers respond to ribavirin, an antiviral medication but for this to be effective it must be administered relatively early after the infection is established. However, most haemorrhagic fever viruses, including Ebola, can only be treated with supportive care. This includes maintaining blood pressure, oxygen levels, and fluid and electrolyte balances; and protecting against secondary infections. Attempts will also be made to reduce haemorrhaging, and replace blood loss through blood transfusions. Patients are hospitalised in an isolation unit and will likely need intensive care.
Recovery and fatality rates from the different haemorrhagic fevers are variable. The filoviruses are among the most dangerous; reported fatality rates for Ebola range from 50-90%. By comparison, dengue hemorrhagic fever has a 1-5% fatality rate. Early diagnosis and proper treatment may help improve the chances of survival from haemorrhagic fevers. Survivors usually require a long convalescence period, and permanent disability can occur with some of these diseases. About 10% of people with Rift Valley fever suffer retinal damage and may become permanently blind, and 25% of South American haemorrhagic fever patients suffer potentially permanent deafness. Survivors do seem to gain lifelong immunity against the virus that made them ill.
Vector control and personal protection measures can help prevent haemorrhagic fevers. Attempts have been made in some highly-populated endemic areas to destroy vector populations, for example of mosquitoes (which can transmit Yellow fever, Dengue and Rift Valley fever). Other measures such as insect repellents and mosquito nets can help to reduce exposure.
There are vaccines available against a few haemorrhagic fevers, notably the yellow fever vaccine, which was developed by a South African scientist. Vaccines against other haemorrhagic fevers are being researched.
There are few established primary prevention measures against Ebola, because the identity and location of its natural reservoir are unknown.
Health-care providers must be able to recognise a case of Ebola in order to prevent it spreading within health-care facilities. They should use haemorrhagic fever isolation precautions and barrier nursing techniques, such as wearing protective clothing; and taking infection-control measures, including equipment sterilisation. If a patient with Ebola dies, it is important that direct contact with the body be prevented.
When to call a doctor
If you have travelled to an area endemic for Ebola or another haemorrhagic disease, or if you know you have been exposed to one of these viruses, consult your doctor. Call your doctor immediately if think you may possibly have been exposed to a haemorrhagic fever, and you develop any symptoms. Note that there are many other causes of severe bleeding; not every instance of fever with haemorrhaging is a viral haemorrhagic fever.
Reviewed by Prof Eftyhia Vardas, University of the Witwatersrand