Ebola Virus

The Ebola outbreak in West Africa killed thousands and spurred efforts to improve responses to pandemics.

Last updated June 12, 2017

A Red Cross worker sprays bleach to disinfect children in Forecariah, Guinea. Misha Hussain/Reuters
Current political and economic issues succinctly explained.

More on:

Public Health Threats and Pandemics

Sub-Saharan Africa




The Ebola virus disease, formerly called the Ebola hemorrhagic fever, was first identified in rural Zaire (now the Democratic Republic of Congo, or DRC) in 1976. The disease had mostly been confined to relatively small outbreaks in rural settings until its 2014 outbreak, when it hit urban areas in Guinea, Liberia, and Sierra Leone, infecting more than 28,600 people and killing more than 11,300 by the end of 2015. The World Health Organization (WHO), which was criticized for its slow response to the epidemic, called the outbreak "the most severe, acute health emergency seen in modern times." West Africa was declared free of the disease in January 2016, but a 2017 outbreak in the DRC has raised concerns about its possible resurgence.

What is Ebola?

Ebola is a severe and often fatal illness that attacks the immune system and causes extreme fluid loss in its victims. The disease disrupts the blood-clotting system, which can lead to internal and external bleeding. Early symptoms include fever, muscle pain, headache, and sore throat, and are followed by vomiting, diarrhea, rash, and bleeding. Most fatalities are caused by severe dehydration or low blood pressure related to fluid loss. The virus is named after the Ebola River in the Congolese region where it was first identified. The largest outbreak prior to 2014 was in Uganda in 2000, in which 425 people were infected and 224 died.

How is it transmitted?

Ebola is transmitted through bodily fluids from an infected person with apparent symptoms or by handling a victim’s corpse. Unlike the common flu and the measles, Ebola is relatively difficult to contract. In October 2014 the New England Journal of Medicine estimated the infection rate (denoted as R0) in that outbreak was between R1.7 and R2 in Liberia, Sierra Leone, and Guinea; on average, each sick person infected between 1.7 and 2 other people. An outbreak is considered "out of control" once it passes R2.

What’s the best way to contain Ebola?

Ebola can by contained by enforcing quarantines of the sick and keeping the exposed away from the general population for the virus’s twenty-one-day incubation period. Potential Ebola carriers can be screened for symptoms and travel history, a measure that was applied to individuals traveling abroad from West Africa during the outbreak. Health-care workers must use protective equipment designed to resist the virus. The U.S. Centers for Disease Control and Prevention (CDC) released revised guidelines in October 2014 to prevent misuse of the gear; the regulations call for training on and supervision of the donning and disrobing of the suits.

In the 2014 outbreak, people in high-transmission countries were told to avoid physical contact, such as hugs and handshakes. Officials also urged families to bring sick relatives into clinics instead of caring for them at home. Because the corpses of Ebola victims can be even more infectious than living victims, health workers warned against traditional burial rituals, which include washing and touching the dead; instead, the dead were buried in deep mass graves.

Vaccinations and treatments for Ebola have undergone clinical trials, and health workers have used ring vaccination—vaccinating primary and secondary contacts of infected persons—to contain the disease. The U.S. Food and Drug Administration (FDA) in September 2015 awarded fast-track status to ZMapp, an experimental drug used to treat some cases of Ebola. In May 2017, DRC officials announced they would begin using an experimental vaccine known as rVSV-ZEBOV to contain the disease’s reemergence there. Treatments also include rehydration and plasma infusions from Ebola survivors, who are believed to possess antibodies to the disease.

Other measures suggested to prevent the disease from spreading outside of West Africa were more controversial, and their efficacy more questionable. Some U.S. politicians called for travel bans on the countries hit the hardest. Little evidence suggested that travel bans would effectively lower transmission, and the policy was never enacted.

Why did the outbreak occur in West Africa?

The outbreak is believed to have started in December 2013 in a Guinean village in the prefecture of Gueckedou, near the Liberian and Sierra Leonean borders. The New England Journal of Medicine traced the disease to a two-year-old boy who died on December 6; he and his family were never tested for the disease, although their symptoms were consistent with those of Ebola (his mother, sister, and grandmother subsequently became sick and died). Researchers do not know how the family caught the virus, which can be contracted from contact with primates, bats, or contaminated food.

Ebola is more a symptom of a weak health-care system than anything else.
Paul Farmer, Physician and Public-Health Expert

Unlike past outbreaks, which were generally confined to remote villages in central Africa (most previous outbreaks occurred in the DRC, Gabon, Sudan, and Uganda), this epidemic hit several communities before being identified as Ebola. By the time the first diagnosis was made, in early March 2014, the virus had already struck multiple communities in Guinea, and cases were already suspected in Liberia and Sierra Leone. Cases were also reported in Nigeria, Senegal, and Mali, although by January 2015 these three had been declared free of Ebola.

Many experts have noted that the spread of the disease was in part caused by increased travel between villages in Gueckedou to cities in Guinea and across nearby borders to Liberia or Sierra Leone, where the disease spread rapidly. Deforestation may also have played a role. Human incursion into previously untouched land increases contact between humans and animals that may carry the disease.

The disease’s ability to spread was largely due to the stricken countries’ poor health-care systems. Prior to the Ebola outbreak there had only been fifty doctors in Liberia, a little more than one per hundred thousand (there are around 240 doctors for every hundred thousand people in the United States). Physician and public-health expert Paul Farmer has written that "Ebola is more a symptom of a weak health-care system than anything else," adding that with proper supplies and trained personnel, the disease could have a 90 percent cure rate.

What was the international response?

International organizations and foreign governments were slow to respond. The nongovernmental organization Doctors Without Borders (often known by is French acronym, MSF) sent doctors to the region as early as March 2014 and called the outbreak "unprecedented" on March 31, but the WHO, hobbled by recent budget cuts, did not declare a health emergency until August.

In September 2014, donor countries led by the United States and the United Kingdom ramped up their financial commitments to combatting Ebola. Direct foreign aid was distributed along historical lines: The United States led relief efforts in Liberia, a country founded by freed U.S. slaves, and the United Kingdom and France led efforts in their former colonies Sierra Leone and Guinea, respectively.

By the end of 2015, the United States had pledged more than $2 billion and deployed military personnel to provide medical and logistical support. The World Bank reported that it had mobilized $1.62 billion [PDF]. Individual donations—including $50 million from the Bill and Melinda Gates Foundation and $25 million from Facebook CEO and founder Mark Zuckerberg and his wife Priscilla Chan—have trumped many countries’ efforts. The international aid agency Oxfam called on countries in January 2015 to implement a “Marshall Plan” for Liberia, Sierra Leone, and Guinea, and countries at a UN conference on post-Ebola recovery in July 2015 pledged an estimated $5.2 billion [PDF].

As the outbreak receded, many of the donor-country-funded treatment centers sat empty. In April 2015, the New York Times reported that the eleven U.S. treatment centers built between November and January 2015 in Liberia had only treated twenty-eight Ebola patients. Some health officials argued that aid would have been better spent on rebuilding the country’s health system and backing existing local efforts.

How many people were affected?

By the end of 2015, more than 28,600 people had been infected, killing more than 11,300. That figure was much lower than projections the CDC made a year before, which calculated that as many as 1.4 million people could become infected with Ebola by January 2015. Instead, the disease peaked in late 2014: in Liberia in September, Guinea in October, and Sierra Leone in November. By January 2016, the WHO declared Guinea and Liberia free of Ebola; Sierra Leone was declared free of the disease in March. A country is classified as Ebola-free once six weeks have passed without a reported case.

Health officials had warned that there would be small flare-ups of the disease because the virus can persist in the bodily fluids of survivors. The DRC declared an outbreak, first detected in Bas-Uele province, in May 2017, following three deaths from the disease. WHO reported later that month that a fourth person had died of Ebola and that it was investigating two confirmed cases and more than forty suspected ones.

What are the long-term consequences of the outbreak?

The Ebola outbreak devastated the economies of Guinea, Liberia, and Sierra Leone. The World Bank estimated in May 2016 that the outbreak cost these three countries a total of $2.8 billion [PDF] ($600 million, $300 million, and $1.9 billion, respectively). Gross domestic product (GDP) growth rates fell dramatically in 2015, from 2.3 percent to 0.1 percent in Guinea, from 8.7 percent in 2013 to 0 percent in Liberia, and from 20.7 percent to -20.6 percent in Sierra Leone, according to World Bank figures. However, growth forecasts for 2016 were positive: 5.2 percent in Guinea, 2.5 percent in Liberia, and 3.9 percent in Sierra Leone.

For many, the 2014 outbreak was a preview of pandemics to come: Increased mobility, greater urbanization, and human encroachment into wild areas will likely lead to more epidemics. Experts say the top threats include influenza and drug-resistant bacteria. The WHO convened an advisory group to address some of the criticisms that emerged during the outbreak, including claims that the organization was influenced by some officials who wanted to downplay the risks of the outbreak. In November 2015, David Nabarro, the UN special envoy for Ebola, announced recommendations [PDF], which received the backing of Margaret Chan, who was then the WHO director-general. They included strengthening and consolidating emergency response efforts, ensuring independent oversight of the organization, and protecting the WHO from political meddling.

However, experts have criticized the organization for failing to reform since then and say that Tedros Adhanom Ghebreyesus, who was elected as Chan’s successor in May 2017, should revive the effort to make changes within the WHO amid the disease’s reemergence. In addition to the DRC government’s proposed response budget of $14 million, the WHO called on donors in late May to contribute $10 million [PDF] for response over the next six months.


Resources Up

CFR's Laurie Garrett examines what the global health community can learn from the Ebola outbreak in this Foreign Policy article.

CFR's Stewart M. Patrick discusses WHO reform in this blog post.

The World Health Organization's Ebola Fact Sheet outlines basic facts, symptoms, and the history of the Ebola virus.

Doctor and Partners in Health founder Paul Farmer reports on the frontlines of the fight against Ebola.

This New York Times multimedia feature traces the Ebola outbreak.