Ebola

Ebola virus disease, sometimes called Ebola hemorrhagic fever, is a severe illness that spreads from animals to humans and affects people and other primates. It is caused by four of the six known ebolaviruses. After infection, symptoms can appear anywhere from two days to three weeks later. Early signs include fever, sore throat, muscle pain, and headaches. These are often followed by vomiting, diarrhea, a rash, and problems with the liver and kidneys. At this point, some people start bleeding internally and externally. Outbreaks have killed between 25 and 90 percent of those infected, with an average death rate around 50 percent. Which virus causes the illness and how quickly treatment begins both strongly influence the outcome. Death usually results from shock due to fluid loss and typically happens six to sixteen days after the first symptoms appear.

The viruses have caused outbreaks in sub-Saharan Africa since 1976, when the disease was first reported. The largest outbreak was the 2013–16 epidemic in West Africa. The virus spreads through direct contact with body fluids like blood from infected people or animals, or through contact with items recently contaminated with those fluids. There is no evidence of airborne spread between humans or other primates, either in nature or in labs. After recovery, the virus can remain in semen or breast milk for weeks to months. Fruit bats are thought to be the natural host; they can carry and spread the virus without getting sick. Ebola symptoms can look like those of malaria, cholera, typhoid fever, meningitis, and other viral hemorrhagic fevers. Diagnosis is confirmed by testing blood for viral RNA, antibodies, or the virus itself.

Controlling outbreaks requires coordinated medical services and community involvement. This includes quickly finding cases, tracing contacts, providing lab services, caring for the sick, and safely disposing of the dead through cremation or burial. Prevention involves wearing protective clothing, washing hands near patients, handling bushmeat carefully, and cooking it thoroughly. Two treatments—atoltivimab/maftivimab/odesivimab and ansuvimab—have been shown to improve outcomes. Early supportive care, such as oral rehydration therapy with slightly sweetened and salty water or intravenous fluids, along with treating symptoms, greatly increases survival chances compared to late treatment. An Ebola vaccine was approved by the U.S. Food and Drug Administration in December 2019. In October 2020, atoltivimab/maftivimab/odesivimab (Inmazeb) was approved in the United States to treat disease caused by Zaire ebolavirus.

The incubation period—time from exposure to symptom onset—ranges from 2 to 21 days, usually 4 to 10 days. Mathematical models suggest about 5 percent of cases may take longer than 21 days. Symptoms often start suddenly with flu-like signs: fatigue, fever over 38.3°C (101°F), weakness, loss of appetite, muscle and joint pain, headache, and sore throat. Nausea, vomiting, diarrhea, abdominal pain, and sometimes hiccups follow. Severe vomiting and diarrhea can cause dehydration. Later, shortness of breath, chest pain, swelling, headaches, and confusion may occur. About half of cases develop a flat red rash with small bumps five to seven days after symptoms begin.

Bleeding, both internal and external, can happen in some cases, usually starting five to seven days after the first symptoms. All infected people have reduced blood clotting. Bleeding from mucous membranes or needle puncture sites occurs in 40–50 percent of cases. This can lead to vomiting blood, coughing up blood, or blood in stool. Bleeding into the skin can cause tiny red spots, larger purple patches, bruising, or hematomas, especially around injection sites. Bleeding into the whites of the eyes is also possible. Heavy bleeding is rare; when it occurs, it is usually in the gastrointestinal tract. In the 2001 Gabon outbreak, gastrointestinal bleeding was reported in about 58 percent of cases, but in the 2014–15 U.S. outbreak it was about 18 percent, possibly due to better prevention of a clotting disorder called disseminated intravascular coagulation.

Recovery can begin between seven and 14 days after first symptoms. Death, when it happens, typically occurs six to sixteen days after the first symptoms and is often due to shock from fluid loss. Bleeding generally signals a worse outcome, and blood loss can lead to death. People near the end of life are often in a coma. Survivors may have ongoing muscle and joint pain, liver inflammation, hearing loss, continued tiredness and weakness, reduced appetite, and trouble regaining their pre-illness weight. Vision problems can also develop. It is recommended that survivors use condoms for at least twelve months after infection, or until a male survivor’s semen tests negative for the virus twice. Survivors develop antibodies that last at least 10 years, but it is not known if these fully protect against future infections.

The disease in humans is caused by four of six viruses in the genus Orthoebolavirus: Bundibugyo ebolavirus (BDBV), Sudan ebolavirus (SUDV), Taï Forest ebolavirus (TAFV), and Zaire ebolavirus (EBOV). EBOV is the most dangerous of these.