Ebola virus disease (EVD), (Ebola hemorrhagic fever (EHF)) or simply Ebola is a disease of humans and other mammals caused by ebolavirus. Signs and symptoms typically start between two days and three weeks after contracting the virus, with a fever, sore throat, muscle pain and headaches. Then, vomiting, diarrhea and rash usually follows, along with decreased function of the liver and kidneys. Around this time, some people begin to bleed both internally and externally. Death, if it occurs, is typically six to sixteen days after symptoms appear and is often due to low blood pressure from fluid loss.
The virus is acquired by contact with blood or other body fluids of an infected human or other animal. This may also occur by direct contact with a recently contaminated item. Spread through the air has not been documented in the natural environment. Fruit bats are believed to be the normal carrier in nature, able to spread the virus without being affected. Humans become infected by contact with the bats or a living or dead animal that has been infected by bats. Once human infection occurs, the disease may spread between people as well. Male survivors may be able to transmit the disease via semen for nearly two months. To diagnose EVD, other diseases with similar symptoms such as malaria, cholera and other viral hemorrhagic fevers are first excluded. Blood samples are tested for viral antibodies, viral RNA, or the virus itself to confirm the diagnosis.
Outbreak control requires a coordinated series of medical services, along with a certain level of community engagement. The necessary medical services include rapid detection and contact tracing, quick access to appropriate laboratory services, proper management of those who are infected, and proper disposal of the dead through cremation or burial. Prevention includes decreasing the spread of disease from infected animals to humans. This may be done by only handling potentially infected bush meat while wearing proper protective clothing and by thoroughly cooking it before consumption. It also includes wearing proper protective clothing and washing hands when around a person with the disease. Samples of body fluids and tissues from people with the disease should be handled with special caution.
No specific treatment for the disease is yet available. Efforts to help those who are infected are supportive and include giving either oral rehydration therapy (slightly sweetened and salty water to drink) or intravenous fluids. This supportive care improves outcomes. The disease has a high risk of death, killing between 25% and 90% of those infected with the virus (average is 50%). EVD was first identified in an area of Sudan (now part of South Sudan), as well as in Zaire (now the Democratic Republic of the Congo). The disease typically occurs in outbreaks in tropical regions of sub-Saharan Africa. From 1976 (when it was first identified) through 2013, the World Health Organization reported a total of 1,716 cases. The largest outbreak to date is the ongoing 2014 West African Ebola outbreak, which is currently affecting Guinea, Sierra Leone, and Liberia. As of 14 October 2014, 9,216 suspected cases resulting in the deaths of 4,555 have been reported. Efforts are under way to develop a vaccine; however, none yet exists.
Signs and symptoms
Signs and symptoms of Ebola.
The time between exposure to the virus and the development of symptoms of the disease is usually 2 to 21 days. Estimates based on mathematical models predict that around 5% of cases may take greater than 21 days to develop.
Symptoms usually begin with a sudden influenza-like stage characterized by feeling tired, fever, pain in the muscles and joints, headache, and sore throat. The fever is usually greater than 38.3 °C (100.9 °F). This is often followed by: vomiting, diarrhea and abdominal pain. Shortness of breath and chest pain may occur next along with swelling, headaches and confusion. In about half of cases the skin may develop a maculopapular rash (a flat red area covered with small bumps).
In some cases, internal and external bleeding may occur. This typically begins five to seven days after first symptoms. All people show some decreased blood clotting. Bleeding from mucous membranes or from sites of needle punctures is reported in 40–50% of cases. This may result in the vomiting of blood, coughing up of blood or blood in stool. Bleeding into the skin may create petechiae, purpura, ecchymoses, hematomas (especially around needle injection sites). There may also be bleeding into the whites of the eyes. Heavy bleeding is uncommon and if it occurs is usually within the gastrointestinal tract.
Recovery may begin between 7 and 14 days after the start of symptoms. Death, if it occurs, is typically 6 to 16 days from the start of symptoms and is often due to low blood pressure from fluid loss. In general, the development of bleeding often indicates a worse outcome and this blood loss can result in death. People are often in a coma near the end of life. Those who survive often have ongoing muscle and joint pain, liver inflammation, and decreased hearing among other difficulties.
CauseMain articles: Ebolavirus (taxonomic group) and Ebola virus (specific virus)
Ebola virus disease in humans is caused by four of five viruses in the genus Ebolavirus. The four are Bundibugyo virus (BDBV), Sudan virus (SUDV), Taï Forest virus (TAFV), and one called, simply, Ebola virus (EBOV, formerly Zaire Ebola virus). Ebola virus is the only member of the Zaire ebolavirus species and the most dangerous of the known EVD-causing viruses, as well as being responsible for the largest number of outbreaks. The fifth virus, Reston virus (RESTV), is not thought to cause disease in humans, but has caused disease in non-human primates. These five viruses are closely related to marburgviruses.
Life cycles of the Ebolavirus
Bushmeat being prepared for cooking in Ghana, 2013. Human consumption of equatorial animals in Africa in the form of bushmeat has been linked to the transmission of diseases to people, including Ebola.
The spread of Ebola between people occurs only by direct contact with the blood or body fluids of a person after symptoms have developed. Body fluids that may contain ebolaviruses include saliva, mucus, vomit, feces, sweat, tears, breast milk, urine, and semen. Entry points include the nose, mouth, eyes, or open wounds, cuts and abrasions. Contact with objects contaminated by the virus, particularly needles and syringes may also transmit the infection. The virus is able to survive on objects for a few hours in a dried state and can survive for a few days within body fluids. Ebola virus may be able to persist in the semen of survivors for up to seven weeks after recovery, which could give rise to infections via sexual intercourse. Otherwise, people who have recovered are not infectious. The potential for widespread infections in countries with medical systems capable of observing correct medical isolation procedures is considered low. Usually when someone has symptoms, they are sufficiently unwell that they are unable to travel without assistance.
Handling infected dead bodies is a risk, including embalming. Because dead bodies are still infectious, traditional burial rituals may spread the disease. Nearly two thirds of the cases of Ebola infections in Guinea during the 2014 outbreak are believed to have been contracted via unprotected (or unsuitably protected) contact with infected corpses during certain Guinean burial rituals.
Healthcare workers treating those who are infected are at greatest risk of disease. This occurs when they do not wear appropriate protective clothing such as masks, gowns, gloves and eye protection. This is particularly common in parts of Africa where the health systems function poorly and where the disease mostly occurs. Hospital-acquired transmission has also occurred in African countries due to the reuse of needles. Some healthcare centers caring for people with the disease do not have running water. In the United States, spread has occurred due to inadequate isolation.
While it is not entirely clear how Ebola initially spreads from animals to human, it is believed to involve direct contact with an infected wild animal or fruit bat. In Africa wild animals, known as bushmeat, are hunted to eat.
Airborne transmission has not been documented during EVD outbreaks. Transmission among rhesus monkeys via breathable 0.8–1.2 μm aerosolized droplets has been demonstrated in the laboratory. That airborne transmission does not appear to occur in humans may be due to there not being high enough levels of the virus in the lungs. Spread by water or food other than bushmeat has also not been observed, nor has spread by mosquitos or other insects.
Reservoir Bats are considered the most likely natural reservoir of ebola virus. Plants, arthropods, and birds have also been considered. In the wild, transmission may occur when infected fruit bats drop partially eaten fruits or fruit pulp, then land mammals such as gorillas and duikers may feed on these fallen fruits. This chain of events forms a possible indirect means of transmission from the natural host species to other animal species, which has led to research into viral shedding in the saliva of fruit bats. Fruit production, animal behavior, and other factors vary at different times and places that may trigger outbreaks among animal populations.
Bats were known to reside in the cotton factory in which the first cases of the 1976 and 1979 outbreaks were observed, and they have also been implicated in Marburg virus infections in 1975 and 1980. Of 24 plant species and 19 vertebrate species experimentally inoculated with EBOV, only bats became infected. The bats displayed no clinical signs and is evidence that these bats are a reservoir species of the virus. In a 2002–2003 survey of 1,030 animals including 679 bats from Gabon and the Republic of the Congo, 13 fruit bats were found to contain EBOV RNA fragments. As of 2005, three types of fruit bats (Hypsignathus monstrosus, Epomops franqueti, and Myonycteris torquata) have been identified as being in contact with EBOV. They are now suspected to represent the EBOV reservoir hosts.Antibodies against Zaire and Reston viruses have been found in fruit bats in Bangladesh, thus identifying potential virus hosts and signs of the filoviruses in Asia.
Between 1976 and 1998, in 30,000 mammals, birds, reptiles, amphibians and arthropods sampled from outbreak regions, no Ebola virus was detected apart from some genetic traces found in six rodents (Mus setulosus and Praomys) and one shrew (Sylvisorex ollula) collected from the Central African Republic. Traces of EBOV were detected in the carcasses of gorillas and chimpanzees during outbreaks in 2001 and 2003, which later became the source of human infections. However, the high lethality from infection in these species makes them unlikely as a natural reservoir.
First U.S. victim remembered for compassionThomas Eric Duncan was remembered Saturday as a big-hearted and compassionate man whose virtues may have led to his infection with Ebola in his native Liberia and death as the first victim of the disease in the United States.
Family and friends gathered Saturday at a Southern Baptist church with a primarily Liberian flock in the North Carolina city of Salisbury, near where Duncan's mother lives.