Ebola Outbreaks: Causes, Prevention, and Control
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Ebola Outbreaks: Why They Happen and How to Stop Them

Ebola Outbreaks: Why They Happen and How to Stop Them
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Updated on January 30, 2025
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The often-deadly Ebola virus disease (EVD) is confined mostly to Africa, but because of how globally connected the world is today, it is regarded as a possible health threat worldwide. Still, only a very small number of cases have ever been detected in the United States.


Because Ebola has the potential to rapidly spread severe illness, keeping the disease contained and preventing outbreaks is vital to global health. Making this happen requires increased efforts to educate people about the virus, stop its transmission, and provide effective treatment.

What Is Ebola?

EVD gets its name from the Ebola River in the Congo, where it was first identified in 1976. It was formerly known as Ebola hemorrhagic fever because it can cause extensive internal and external bleeding and impaired organ function.

 Other symptoms include aches, pains, fatigue, fever, diarrhea, and vomiting.

Six strains of the virus have been identified, each named after the area where it was discovered. Four of them 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)
  • Bundibugyo virus (Bundibugyo ebolavirus)
The Zaire ebolavirus, often referred to simply as the Ebola virus, is the deadliest, with a mortality rate of up to 90 percent.

When Have Ebola Outbreaks Happened?

The Bundibugyo ebolavirus has resulted in two outbreaks. The first was in Uganda in 2007 and 2008, when it was first discovered. This outbreak caused 149 cases and 37 deaths. The second was in the Democratic Republic of the Congo in 2012 and caused 36 cases and 13 deaths.

Between 2014 and 2016, more than 28,600 cases and 11,325 deaths from the Zaire ebolavirus were reported in West Africa, making it the largest outbreak so far. During the course of that epidemic, the disease made its way outside of Africa to Italy, Spain, the United Kingdom, and the United States.


In an outbreak of the Sudan ebolavirus in Uganda between the fall of 2022 and early 2023, 164 cases were recorded (22 probable and 142 confirmed), and 55 deaths were confirmed.

Ebola in the United States

During the 2014–2016 outbreak, a total of 11 people with Ebola were treated in the United States. Nine contracted the illness while in West Africa. Two became ill while on American soil, both of whom were nurses treating an Ebola patient from Liberia who had traveled to the United States. Both nurses survived.

So far, only these two people have contracted Ebola while in the United States, and nobody has become ill on American soil and died.

Why Do New Ebola Outbreaks Happen?

Researchers believe new strains appear after developing in an animal and transmitting to humans who come in close contact with the infected animal’s bodily fluids. This is called a “spillover event.”

Fruit bats are suspected of being reservoirs of Ebola, meaning they don’t become sick when infected, but the virus can develop within them. People may contract Ebola through contact with bat droppings.

In parts of Africa, fruit bats are also eaten, and infection may spread when preparing the meat for consumption.

Other animals that may carry the virus include chimpanzees, gorillas, monkeys, forest antelope, rodents, and porcupines. There is no evidence that the disease can be transmitted through mosquitoes or other insects. Also, unlike the flu or COVID-19, Ebola does not spread through the air via respiratory droplets.

How Do Ebola Outbreaks Spread?

Once a human has Ebola, the virus can then be passed on through contact with broken skin or mucous membranes, or via exposure to:

  • Saliva
  • Urine
  • Sweat
  • Tears
  • Feces
  • Breast milk
  • Vomit
  • Semen
  • Vaginal secretions
Ebola may also spread through:

  • Consuming bushmeat (meat from wild animals)
  • Traditional burial practices involving washing and touching the deceased
  • Contact through caring for the sick without sufficient protective equipment
  • Handshakes when greeting others
Deforestation, climate change, and human encroachment into natural habitats have also put people in closer proximity to wild animals, increasing the chances of contact and transmission.

Another factor contributing to Ebola spread is poverty, as impoverished people are more likely to live in close proximity to possibly ill family members, have less sanitary conditions, and may be more likely to eat bushmeat. Additionally, unsanitary conditions in crowded healthcare facilities have been cited as a principal means of transmission.


While travelers and the general public are at little risk of contracting Ebola, health officials recognize that cross-border travel can fuel outbreaks. In 2014, the proliferation of Ebola cases was traced to people who traveled to the capital cities of Guinea, Liberia, and Sierra Leone.

This prompted the World Health Organization (WHO) to recommend that countries with Ebola transmission conduct exit screenings at international airports, seaports, and major land crossings to identify and isolate anyone who may have Ebola.


Researchers also found that delayed virus detection can be a key factor in contributing to a rapid expansion of the illness.

How to Prevent and Control Ebola Outbreaks

When the 2014 Ebola outbreak began, the Centers for Disease Control and Prevention (CDC) recognized that it wasn’t fully prepared if someone with the virus entered the United States and spread the illness. The CDC sprang into action, amplifying the efforts of the WHO and national and community programs in Africa with measures including:

  • Testing Recognizing the need to diagnose Ebola quickly, the CDC distributed lab tests to state and local public health laboratories in West Africa that could reliably detect infection.
  • Education The CDC moved to educate healthcare providers on how to identify patients suspected of having Ebola and isolate them.

  • Medication Two treatments are currently available to treat Ebola disease: Inmazeb and Ebanga. These medicines help reduce symptoms and speed up elimination of the infection.

  • Rapid Response Teams Epidemiologists, clinicians, laboratory experts, communication officers, social mobilization experts, anthropologists, logisticians, data managers, infection prevention and control specialists, and environmental experts all worked to prevent any spread of the virus.

  • Surveillance Systems Comprehensive infectious disease surveillance systems, including readily accessible testing, were assembled to help diagnose the illness.

  • Community Engagement In Sierra Leone during the 2014 outbreak, workers went door to door to reach 1.5 million households and share information on ways families could protect themselves against Ebola virus disease, helping to slow transmission.

  • Vaccination Since 2019, two vaccine options have been developed for those at high risk of exposure to Ebola: Ervebo and Zabdeno.

     CDC researchers found that Ervebo has likely played an important role in limiting Ebola illnesses and deaths since its introduction.

  • International Cooperation and Support The organization Global Ebola Response says that countries large and small have stepped up to provide doctors, mobile clinics, and funding to help combat the virus. Globally, health officials recognize Ebola as a potential large-scale threat, so international cooperation is vital.

The Takeaway

  • Ebola is one of the deadliest infectious diseases of the modern era, with outbreaks so far contained to Africa.
  • Public health officials around the globe have been working together to take measures to prevent its transmission.
  • New vaccines and therapeutics, improved surveillance, and increased community education are helping to keep the disease from becoming more widespread.

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Jane Yoon Scott, MD

Medical Reviewer

Jane Yoon Scott, MD, is an infectious disease physician and an assistant professor of medicine at Emory University in Atlanta. Dr. Scott enjoys connecting with her patients, empowering them to understand and take ownership of their health, and encouraging them to ask questions so that they can make informed and thoughtful decisions.

She graduated with the highest honors from the Georgia Institute of Technology, then received her MD from the Medical College of Georgia. She completed her internal medicine residency training and chief residency at Temple University Hospital, as well as a fellowship in infectious diseases at Emory University. She is board-certified in both internal medicine and infectious diseases.

When she is not seeing patients, Dr. Scott works with neighboring health departments to promote public health, especially to communities that have been historically underserved. She also teaches medical trainees and lectures medical students at the Emory University School of Medicine.

In her free time, Dr. Scott appreciates a good coffee shop, weekend hikes, playing guitar, strolling through cities, sampling restaurants, and traveling to new places.

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Don Rauf has been a freelance health writer for over 12 years and his writing has been featured in HealthDay, CBS News, WebMD, U.S. News & World Report, Mental Floss, United Press International (UPI), Health, and MedicineNet. He was previously a reporter for DailyRx.com where he covered stories related to cardiology, diabetes, lung cancer, prostate cancer, erectile dysfunction, menopause, and allergies. He has interviewed doctors and pharmaceutical representatives in the U.S. and abroad.

He is a prolific writer and has written more than 50 books, including Lost America: Vanished Civilizations, Abandoned Towns, and Roadside Attractions. Rauf lives in Seattle, Washington.

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