A History of Ebola in 24 Outbreaks

Ebola is of the forest

Ebola was named after a river, but in hindsight it would have been more fitting to name it after a forest. The Ebola virus lives in the deep equatorial forests of Central Africa, and can infect people who live, hunt or work in the forest or on its fringes.

The Forest Region of Guinea, where the current outbreak began, had had no known outbreaks. But it is one of several areas in Africa thought to have the right combination of forest, bats, temperature and other environmental conditions to possibly harbor the Ebola virus.

Ebola moves from animals to humans

Ebola kills apes, monkeys and humans. But the virus needs a more tolerant host, probably bats, to survive over long periods.

Contaminated bats can carry the virus across rivers and borders and can infect animals who touch their blood or eat fruit they have gnawed on.

At least 10, and probably most, of the 24 outbreaks across Africa began with a person touching the blood or meat of an infected ape, monkey, bat or other animal killed for bush meat.

Ebola thrives on delayed diagnosis

Before the current Ebola outbreak in West Africa, there were eight previous outbreaks with more than 100 cases.

It took an average of two months for each of the eight previous large outbreaks to be recognized and investigated. After each outbreak was announced, it took an average of three weeks to mount an international response.

Small, contained outbreaks of Ebola are relatively easy to stop, but long delays in recognizing an outbreak allow chains of infection to continue unbroken.

Ebola travels by road

Most Ebola outbreaks begin in remote forested areas. For the virus to leave the forest and travel long distances in humans, it must go by road or river.

Where people have access to motorcycles, taxis or buses, Ebola tends to spread from village to village along roads.

Roadblocks are usually thought to be ineffective, because people can bribe their way through or find alternate routes.

Ebola strikes unprepared hospitals

Hospitals and clinics are the best places to recognize Ebola. But unprepared hospitals can concentrate and amplify an outbreak.

At least 11 of the 24 outbreaks have spread through hospitals or clinics, often decimating medical staff.

The risk of amplifying an outbreak is lower when doctors and nurses isolate infected patients, wear protective gear and disinfect or burn contaminated waste.

A World Health Organization report written in 1978, two years after the first Ebola outbreak, said:

“The hospital, especially the referral hospital, is the site where such outbreaks can either be recognized and halted, or unrecognized and disseminated. With them rests the responsibility for stopping the spread of these dangerous diseases.”

Ebola benefits from super-spreader events

At least five “super-spreader” events have been documented in the history of Ebola. These events typically involve one person infecting many others, often at a traditional burial where the body is washed and touched.

Early in the current Ebola outbreak, 12 women were infected at the funeral of a traditional healer in Sierra Leone.

Ebola thrives on fear and distrust

Outbreaks are more difficult to fight when people in affected areas have a poor understanding of the disease or distrust authorities and medical practices.

International response teams typically recruit local students, teachers, volunteers and Ebola survivors to spread information and counter rumors. Posters and pamphlets are often translated into local dialects, and radio skits and advertisements broadcast in areas with access to radio.

Outbreaks are stopped by isolation, careful nursing and contact tracing

Previous Ebola outbreaks have been stopped by isolating and limiting direct physical contact with infected patients, whether they are cared for at home or in a hospital.

As new patients are found, investigators try to find, track and monitor their contacts.

That effort, called contact tracing, is time-consuming work. During the 1976 outbreak of Ebola in Yambuku, Zaire, surveillance teams drove to surrounding villages and interviewed 34,000 families looking for people with symptoms of infection.

Outbreaks are stopped with resources

Summarizing the Ebola outbreak in Yambuku, Zaire, a W.H.O. report in 1978 said:

“No more dramatic or potentially explosive epidemic of a new viral disease has occurred in the world in the past 30 years. ... No better example comes to mind to illustrate the need for national disease surveillance and the prompt solicitation of international assistance, nor of the need for the development of international resources, comprising personnel, equipment, transport, communication and finance, that can be made available in a very few days to cope with such emergencies.”