Ebola virus disease (EVD) or Ebola hemorrhagic fever (EHF) is the human disease caused by the Ebola virus. Symptoms typically start two days to three weeks after contracting the virus, with a fever, sore throat, muscle pains, and headaches.
Typically nausea, vomiting, and diarrhea follow, along with decreased functioning of the liver and kidneys. At this point, some people begin to have bleeding problems.
The virus may be acquired upon contact with blood or bodily fluids of an infected animal (commonly monkeys or fruit bats). Spread through the air has not been documented in the natural environment.
Fruit bats are believed to carry and spread the virus without being affected. 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. In order to make the diagnosis, typically other diseases with similar symptoms such as malaria, cholera and other viral hemorrhagic fevers are first excluded.
Blood samples may then be tested for viral antibodies, viral RNA, or the virus itself to confirm the diagnosis.
Prevention includes decreasing the spread of disease from infected monkeys and pigs to humans. This may be done by checking such animals for infection and killing and properly disposing of the bodies if the disease is discovered.
Properly cooking meat and wearing protective clothing when handling meat may also be helpful, as are wearing protective clothing and washing hands when around a person with the disease. Samples of bodily fluids and tissues from people with the disease should be handled with special caution.
There is no specific treatment for the disease; efforts to help persons who are infected include giving either oral rehydration therapy (slightly sweet and salty water to drink) or intravenous fluids.
The disease has high mortality rate: often killing between 50% and 90% of those infected with the virus.
EVD was first identified in Sudan and 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, fewer than 1,000 people per year have been infected.
The largest outbreak to date is the ongoing 2014 West Africa Ebola outbreak, which is affecting Guinea, Sierra Leone, Liberia and likely Nigeria.
As of August 2014 more than 1600 cases have been identified. Efforts are ongoing to develop a vaccine; however, none yet exists.
Signs and symptoms of Ebola usually begin suddenly with an flu-like stage characterized by fatigue, fever, headaches, and joint, muscle, and abdominal pain.
Vomiting, diarrhea and loss of appetite are also common. Less common symptoms include the following: sore throat, chest pain, hiccups, shortness of breath and trouble swallowing.
The average time between contracting the infection and the start of symptoms is 8 to 10 days, but can occur between 2 and 21 days. Skin manifestations may include a maculopapular rash (in about 50% of cases).
Early symptoms of EVD may be similar to those of malaria, dengue fever, or other tropical fevers, before the disease progresses to the bleeding phase.
Bleeding into the skin may create petechiae, purpura, ecchymoses, and hematomas (especially around needle injection sites).
All people infected show some symptoms of circulatory system involvement, including impaired blood clotting.
Bleeding from puncture sites and mucous membranes (e.g. gastrointestinal tract, nose, vagina and gums) is reported in 40–50% of cases. Types of bleeding known to occur with Ebola virus disease include vomiting blood, coughing it up or blood in the stool.
Heavy bleeding is rare and is usually confined to the gastrointestinal tract. In general, the development of bleeding symptoms often indicates a worse prognosis and this blood loss can result in death.
Life cycles of the Ebolavirus
EVD is caused by four of five viruses classified in the genus Ebolavirus, family Filoviridae, order Mononegavirales. These four viruses are Bundibugyo virus (BDBV), Ebola virus (EBOV), Sudan virus (SUDV), Taï Forest virus (TAFV).
The fifth virus, Reston virus (RESTV), is not thought to be disease-causing in humans. During an outbreak, those at highest risk are health care workers and close contacts of those with the infection.
Human-to-human transmission can occur via direct contact with blood or bodily fluids from an infected person (including embalming of an infected dead person) or by contact with contaminated medical equipment, particularly needles and syringes.
Semen is infectious in survivors for up to 50 days. Transmission through oral exposure and through conjunctiva exposure is likely and has been confirmed in non-human primates.
The potential for widespread EVD infections is considered low as the disease is only spread by direct contact with the secretions from someone who is showing signs of infection.
The quick onset of symptoms makes it easier to identify sick individuals and limits a person's ability to spread the disease by traveling.
Because dead bodies are still infectious, some doctors disposed of them in a safe manner, despite local traditional burial rituals.
Medical workers who do not wear appropriate protective clothing may also contract the disease.
In the past, hospital-acquired transmission has occurred in African hospitals due to the reuse of needles and lack of universal precautions.
Airborne transmission has not been documented during previous EVD outbreaks. They are, however, infectious as breathable 0.8–1.2 micrometre laboratory generated droplets; because of this potential route of infection, these viruses have been classified as Category A biological weapons. Recently the virus has been shown to travel without contact from pigs to non-human primates.
Bats drop partially eaten fruits and pulp, then land mammals such as gorillas and duikers feed on these fallen fruits.
This chain of events forms a possible indirect means of transmission from the natural host to animal populations, which has led to research towards viral shedding in the saliva of bats.
Fruit production, animal behavior, and other factors vary at different times and places that may trigger outbreaks among animal populations.
Bats are considered the most likely natural reservoir of the Ebola virus (EBOV); plants, arthropods, and birds have also been considered.
Bats were known to reside in the cotton factory in which the first cases for the 1976 and 1979 outbreaks were employed, and they have also been implicated in Marburg virus infections in 1975 and 1980.
Between 1976 and 1998, in 30,000 mammals, birds, reptiles, amphibians, and arthropods sampled from outbreak regions, no ebolavirus 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.
Transmission between natural reservoir and humans is rare, and outbreaks are usually traceable to a single case where an individual has handled the carcass of gorilla, chimpanzee, or duiker.
Fruit bats are also eaten by people in parts of West Africa where they are smoked, grilled or made into a spicy soup.
Typically nausea, vomiting, and diarrhea follow, along with decreased functioning of the liver and kidneys. At this point, some people begin to have bleeding problems.
The virus may be acquired upon contact with blood or bodily fluids of an infected animal (commonly monkeys or fruit bats). Spread through the air has not been documented in the natural environment.
Fruit bats are believed to carry and spread the virus without being affected. 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. In order to make the diagnosis, typically other diseases with similar symptoms such as malaria, cholera and other viral hemorrhagic fevers are first excluded.
Blood samples may then be tested for viral antibodies, viral RNA, or the virus itself to confirm the diagnosis.
Prevention includes decreasing the spread of disease from infected monkeys and pigs to humans. This may be done by checking such animals for infection and killing and properly disposing of the bodies if the disease is discovered.
Properly cooking meat and wearing protective clothing when handling meat may also be helpful, as are wearing protective clothing and washing hands when around a person with the disease. Samples of bodily fluids and tissues from people with the disease should be handled with special caution.
There is no specific treatment for the disease; efforts to help persons who are infected include giving either oral rehydration therapy (slightly sweet and salty water to drink) or intravenous fluids.
The disease has high mortality rate: often killing between 50% and 90% of those infected with the virus.
EVD was first identified in Sudan and 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, fewer than 1,000 people per year have been infected.
The largest outbreak to date is the ongoing 2014 West Africa Ebola outbreak, which is affecting Guinea, Sierra Leone, Liberia and likely Nigeria.
As of August 2014 more than 1600 cases have been identified. Efforts are ongoing to develop a vaccine; however, none yet exists.
Signs and symptoms of Ebola usually begin suddenly with an flu-like stage characterized by fatigue, fever, headaches, and joint, muscle, and abdominal pain.
Vomiting, diarrhea and loss of appetite are also common. Less common symptoms include the following: sore throat, chest pain, hiccups, shortness of breath and trouble swallowing.
The average time between contracting the infection and the start of symptoms is 8 to 10 days, but can occur between 2 and 21 days. Skin manifestations may include a maculopapular rash (in about 50% of cases).
Early symptoms of EVD may be similar to those of malaria, dengue fever, or other tropical fevers, before the disease progresses to the bleeding phase.
Bleeding
In the bleeding phase, internal and subcutaneous bleeding may present itself through reddening of the eyes and bloody vomit.Bleeding into the skin may create petechiae, purpura, ecchymoses, and hematomas (especially around needle injection sites).
All people infected show some symptoms of circulatory system involvement, including impaired blood clotting.
Bleeding from puncture sites and mucous membranes (e.g. gastrointestinal tract, nose, vagina and gums) is reported in 40–50% of cases. Types of bleeding known to occur with Ebola virus disease include vomiting blood, coughing it up or blood in the stool.
Heavy bleeding is rare and is usually confined to the gastrointestinal tract. In general, the development of bleeding symptoms often indicates a worse prognosis and this blood loss can result in death.
Causes
Main article: Ebolavirus
The fifth virus, Reston virus (RESTV), is not thought to be disease-causing in humans. During an outbreak, those at highest risk are health care workers and close contacts of those with the infection.
Transmission
It is not entirely clear how Ebola is spread. EVD is believed to occur after an ebola virus is transmitted to an initial human by contact with an infected animal's body fluids.Human-to-human transmission can occur via direct contact with blood or bodily fluids from an infected person (including embalming of an infected dead person) or by contact with contaminated medical equipment, particularly needles and syringes.
Semen is infectious in survivors for up to 50 days. Transmission through oral exposure and through conjunctiva exposure is likely and has been confirmed in non-human primates.
The potential for widespread EVD infections is considered low as the disease is only spread by direct contact with the secretions from someone who is showing signs of infection.
The quick onset of symptoms makes it easier to identify sick individuals and limits a person's ability to spread the disease by traveling.
Because dead bodies are still infectious, some doctors disposed of them in a safe manner, despite local traditional burial rituals.
Medical workers who do not wear appropriate protective clothing may also contract the disease.
In the past, hospital-acquired transmission has occurred in African hospitals due to the reuse of needles and lack of universal precautions.
Airborne transmission has not been documented during previous EVD outbreaks. They are, however, infectious as breathable 0.8–1.2 micrometre laboratory generated droplets; because of this potential route of infection, these viruses have been classified as Category A biological weapons. Recently the virus has been shown to travel without contact from pigs to non-human primates.
Bats drop partially eaten fruits and pulp, then land mammals such as gorillas and duikers feed on these fallen fruits.
This chain of events forms a possible indirect means of transmission from the natural host to animal populations, which has led to research towards viral shedding in the saliva of bats.
Fruit production, animal behavior, and other factors vary at different times and places that may trigger outbreaks among animal populations.
Reservoir
Bats were known to reside in the cotton factory in which the first cases for the 1976 and 1979 outbreaks were employed, and they have also been implicated in Marburg virus infections in 1975 and 1980.
Between 1976 and 1998, in 30,000 mammals, birds, reptiles, amphibians, and arthropods sampled from outbreak regions, no ebolavirus 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.
Transmission between natural reservoir and humans is rare, and outbreaks are usually traceable to a single case where an individual has handled the carcass of gorilla, chimpanzee, or duiker.
Fruit bats are also eaten by people in parts of West Africa where they are smoked, grilled or made into a spicy soup.
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