Ebola virus disease (EVD) is a rare and often-fatal infection caused by one of the five strains of the Ebola virus. Ebola first appeared in 1976 in a simultaneous outbreak in the areas that are now Sudan and the Democratic Republic of the Congo, according to the World Health Organization (WHO). Since then, there have been sporadic outbreaks in Africa.

Worldwide, there have been 28,639 cases of Ebola virus disease and 11,316 deaths as of March 13, 2016, according to the Centers for Disease Control and Prevention (CDC). One of the largest Ebola outbreaks began in March 2014 and, as of March 20, 2016, there have been 28,608 reported Ebola cases from this outbreak, according to the CDC. Of these cases, 15,219 have been confirmed by laboratory testing. The total number of deaths from Ebola is 11,305. More recently, a new Ebola flare-up occurred in Guinea in early 2016, with 800 confirmed Ebola cases as of March 22, 2016.

Causes and origins

The Ebola virus may have initially been transmitted to humans from bats. Derek Gatherer, a bioinformatics researcher at Lancaster University in the United Kingdom, told Live Science that there is a strong circumstantial case that says infection by bats is likely, but scientists haven't actually found strong evidence to support that hypothesis.

Though WHO agrees that bats may be carriers of Ebola, the organization says that Ebola was introduced into the human population through the secretions, blood, organs or other bodily fluids of many different infected animals. Other than bats, some of these animals include monkeys, chimpanzees, gorillas, forest antelope and porcupines.

Some experts think that the quick spread of this virus from Central to West Africa may be due to bats' travel patterns across Africa. Researchers have said that Ebola may have continued to spread within West Africa once it arrived because the outbreak is happening in an underdeveloped area of the world that is unprepared to deal with it.

During the 1976 outbreak in the Republic of Zaïre (now the Democratic Republic of the Congo), 280 people became infected through close contact with one another and through the use of contaminated syringes and needles in clinics and hospitals. Out of those 280 people, only 20 percent of the patients survived. The virus infected 284 people in Sudan. Out of these, 151 (53 percent) of the infected patients died, according to the CDC.

The first Ebola case in the United States was confirmed by the CDC on Sept. 30, 2014. The patient, Thomas Eric Duncan, who had spent time in Liberia before traveling to the United States, died 10 days later in Dallas, Texas. On Oct. 12, 2014, a nurse in Dallas who had been caring for Duncan tested positive for Ebola symptoms, according to the CDC. A second health care worker tested positive for Ebola on Oct. 15, the CDC announced.

Virus

Ebola is a virus in the family Filoviridae and the genus Ebolavirus. Five virus species have been identified, four of which are known to cause disease in humans: Ebola virus (Zaire ebolavirus); Sudan virus (Sudan ebolavirus); Taï Forest virus (Taï Forest ebolavirus, formerly Côte d’Ivoire ebolavirus); and Bundibugyo virus (Bundibugyo ebolavirus). The fifth species, Reston virus (Reston ebolavirus), has not caused disease in humans but has affected nonhuman primates. The virus causing the 2014 West African outbreak belongs to the Zaire species, according to WHO.

In general, to survive, viruses must find a host cell and take it over. The virus also replicates itself so that it can be spread to other host cells. In response to a virus, the human body produces antibodies. "Antibodies are the protein 'workhorses' of the immune system; in less severe infections (like the flu), antibodies stop the virus from spreading and help clear it from the body. The problem with Ebola is that the virus spreads so rapidly that it can easily overcome the body's immune response," said Jonathan Lai, associate professor of biochemistry at Albert Einstein College of Medicine in New York.

Symptoms and diagnosis

Symptoms of EVD may appear two to 21 days after exposure to the Ebola virus, according to WHO. On average, however, symptoms appear within eight to 10 days, the CDC says.

"The symptoms are extremely nonspecific in the beginning — Ebola looks like almost anything," Dr. Bruce Hirsch, an infectious-disease specialist at North Shore University Hospital in Manhasset, New York, told Live Science.

At first, Ebola symptoms seem like those of many other viruses. According to the CDC, the patient will usually experience the following symptoms:

A fever greater than 101.5 degrees Fahrenheit (38.6 degrees Celsius)

Muscle pain

Severe headache

Weakness

Diarrhea

Vomiting

Abdominal pain

Some patients also bleed from the nose and mouth. This is called hemorrhagic syndrome and usually occurs only in the late stages of the disease. Typically, the Ebola virus causes hemorrhagic syndrome in 30 to 50 percent of patients, said Angela Rasmussen, a research assistant professor of microbiology at the University of Washington.

Other symptoms that occur in advanced stages of EVD include rash and symptoms of impaired kidney and liver function, such as blood in the stool, according to WHO.

Because the symptoms of Ebola are so much like those of other diseases, medical professionals use a series of tests to diagnose EVD. According to WHO, common tests include the following:

Virus isolation by cell culture

Antibody-capture enzyme-linked immunosorbent assay (ELISA)

Serum neutralization test

Antigen-capture detection tests

Electron microscopy

Reverse transcriptase polymerase chain reaction (RT-PCR) assay

How is Ebola spread?

Ebola is not an airborne virus. Unlike some other viruses, the Ebola virus can only be spread by body fluids. Therefore, Ebola spreads through human-to-human transmission via direct contact, according to WHO. Direct contact means that blood, secretions, organs or other body fluids containing the virus must come into contact with broken skin or the mucous membranes of a healthy individual in order for the virus to be transmitted. The fluids may come directly from the infected patient or from surfaces touched by the sick individual, such as bedding or clothing.

A WHO Ebola Situation Assessment for Oct. 6, 2014, states that the virus is most easily transmitted through blood, feces and vomit. Breast milk, urine and semen have also been found to transmit the Ebola virus, and it is believed that it may even be transmitted through tears and saliva.

Ebola is not spread through the air. This means that a person cannot contract the virus from breathing the same air as an infected individual. However, if an infected individual directly sneezes on a person and the mucus from that sneeze comes into contact with an open cut or the eyes, nose or mouth of someone else, there is a chance of infection. WHO has not documented cases of this actually happening, though.

Health workers are at the highest risk of contracting Ebola. Health workers are between 21 and 32 times more likely to be infected with Ebola than people in the general adult population, according to WHO, and, two-thirds of those infected have died.

Ebola treatment

There is no cure for Ebola, nor are there any vaccines that can prevent the disease. Those who recover from the disease do so through the strength of their own immune system, according to the CDC. Doctors have found that one of the most important treatments for patients afflicted with the virus is simply keeping them well hydrated and helping them breathe, to give their immune system a better chance to fight off the disease.

Doctors are trying several experimental treatments on patients. Some doctors are giving patients blood transfusions from those who have survived Ebola. The hope is that the survivor's antibodies will help the recipient's immune system fight off the virus. A 1995 study published in the Journal of Infectious Disease found that this treatment may be helpful to reduce the number of deaths from EDV.

ZMapp is one experimental treatment for Ebola. This treatment contains three monoclonal antibodies that may bind to the virus, so that the immune system can clear out the virus. "So far, the published work indicates that ZMapp can cure monkeys up to five days after they've been given a lethal dose of Ebola virus," Lai said. Africa has approved of the use of ZMapp and the United States fast-tracked the drug in 2015 to get quicker Food and Drug Administration approval.

One of the survivors of Ebola, Dr. Kent Brantly, was treated with ZMapp, the Washington Post reported. "Although ZMapp has been provided on a compassionate basis for several people in this current outbreak, we don't have enough numbers to know if the drug is effective in humans from a statistical point of view," Lai said.

Brincidofovir is another experimental treatment for EDV. This oral drug prevents the virus from replicating itself. Its Phase 3 clinical testing was performed in 2015 with disappointing results, according to a report in Globe Newswire. Phase 3 testing means it has been given to large groups of people to confirm its effectiveness, monitor side effects, compare it to commonly used treatments and collect information that will allow the treatment to be used safely, according to the National Institutes of Health.

Recovery and immunity

According to WHO one in three people infected with Ebola survive. As of March 13, 2016, 10,000 people have survived the Ebola virus, according to the CDC. Survivors are often faced with continuing problems. Many are ostracized by their community because of misunderstandings about how the virus is spread, according to the International Federation of Red Cross and Red Crescent Societies. WHO has set up a page that offers insight into the lives of survivors of Ebola.

Ebola can also cause other changes in the body after the virus had been cured. For example, one survivor experienced a change in eye color due to inflammation and very high blood pressure in his left eye, according to a report in The New England Journal of Medicine. When fluid in the eye was tested, it was found to contain the Ebola virus, but was believed to not be contagious. Survivors can also experience persistent insomnia, hearing loss, seizures and body aches.

According to the CDC, research shows that patients who recover from Ebola can develop antibodies that will protect them from the virus for at least 10 years, or possibly even longer. There have been cases recorded, though, where a person who was previously cured of the virus becomes sick months later. It is thought that in some cases the virus can hide from the immune system to avoid being completely destroyed.

Also, after the patient recovers, he or she is no longer contagious. There is one exception, though. A recovered patient can still spread the virus with semen for up to three months after they recover. Doctors advise anyone who is recovering from Ebola to use condoms or to refrain from intercourse for three months.

Prevention

Most people outside of West Africa do not need to worry about Ebola prevention. Only those who live in an area affected by Ebola and medical professionals are in danger of contracting the virus. For those individuals, the CDC has a tip sheet on ways to prevent infection.

Measures are being taken by world health organizations to halt the spread of the disease. In October 2014, WHO and the Liberian Ministry of Health, with support from USAID, created a training program for health workers who are treating patients with Ebola. The program focuses on patient care, infection prevention and control. Six Ebola survivors are helping with the project, to give an inside look at what it is like to have the disease.

Companies are also producing machines that will make disinfection easier for clinics and hospitals. For example, medical device maker Xenex, based in San Antonio, Texas, has developed a robot that uses pulses of ultraviolet UV-C rays to disinfect hospital rooms. The company claims it can rid any room of Ebola in two minutes.

Additional resources