The Centers for Disease Control and Prevention (CDC) says Ebola disease is caused by a group of viruses called orthoebolaviruses. The viruses pass from animals to people, and then between people through contact with body fluids or contaminated objects. The World Health Organization (WHO) says outbreak control relies on a package of measures, from patient care to contact tracing to safe burials.
How the virus reaches people
The CDC says scientists think African fruit bats play a part in how orthoebolaviruses spread, and that the bats may be where the virus comes from. The CDC says infected animals can pass the virus to other animals through infected body fluids or items those fluids have contaminated. The WHO says fruit bats of the Pteropodidae family are thought to be the natural hosts.
The CDC calls it a spillover event when an infected animal spreads the virus to a person. The WHO says people can be infected through close contact with the blood, secretions, organs or other body fluids of animals including porcupines, forest antelope, monkeys, gorillas, chimpanzees or fruit bats that were sick or dead, or that were in the rainforest. The CDC adds that the contact can happen through hunting or preparing the animal’s meat for eating. Several past outbreaks in Gabon and the Republic of the Congo, the CDC reports, were linked to hunters who had close contact with wildlife.
How it passes between people
After a spillover event, the virus can spread from person to person. According to the CDC, a person becomes infected when broken skin, or mucous membranes in the eyes, nose or mouth, come into contact with blood or other body fluids from someone who is ill with Ebola disease or has died of it. The CDC lists urine, saliva, sweat, feces, vomit, breast milk and amniotic fluid as body fluids. Objects contaminated with those fluids, such as clothes, bedding, needles and medical equipment, can also carry the virus.
The CDC says Ebola does not spread the way respiratory viruses such as flu and COVID-19 do, and a person cannot get it simply by being near someone. It also says there is no evidence that mosquitoes or other insects spread the viruses.
The WHO says health and care workers have frequently been infected while treating patients, through close contact when infection control precautions are not strictly followed. It adds that funeral rites in which mourners touch the body of someone who has died can also help the disease spread. The CDC’s history of outbreaks describes the first recognized outbreak, in 1976, as spreading through contaminated needles and syringes at a hospital and clinics, and through close personal contact.
When people can spread it
The CDC and the WHO both say people with Ebola cannot spread the virus before they have symptoms. The WHO says the time from infection to the start of symptoms varies from two to 21 days. It says people remain infectious as long as their blood contains the virus.
The CDC says survivors can at times pass on the virus after their symptoms have ended. This occurs when the virus remains in areas of the body that are protected from the immune system. The CDC names the brain, eyes, placenta and testicles, and says this is rare. The WHO adds that Ebola virus transmission through infected semen has been documented up to 15 months after clinical recovery. The CDC says the presence of the virus in these body parts, and for how long, varies by survivor.
The WHO says it does not recommend isolating recovered patients whose blood has tested negative. For male survivors, it recommends a semen testing program that offers counseling and monthly testing until two tests in a row are negative. Without such a program, the WHO says male survivors should follow safer sex practices for 12 months. The CDC says scientists do not know whether survivors are immune for life, or whether they can be infected with a different species of the virus.
How outbreaks are contained
The WHO says outbreak control relies on a package of interventions. These include intensive supportive care for patients, infection prevention and control, disease surveillance and contact tracing, laboratory services, safe and dignified burials, vaccination if relevant, and social mobilization. The WHO calls community engagement key to controlling any outbreak.
Among its containment measures, the WHO lists identifying people who may have been in contact with someone infected with Ebola disease and monitoring their health for 21 days. It also says the sick should be separated from the healthy, and that patients should be isolated in a designated treatment center for early care and to avoid spread at home.
In health facilities, the WHO says workers should always take standard precautions, including hand hygiene, personal protective equipment and safe injection practices. Those caring for suspected or confirmed Ebola patients should apply extra measures to avoid contact with blood, body fluids and contaminated surfaces or materials. The WHO also says samples from patients are an extreme biohazard risk, and that laboratory testing on non-inactivated samples should be conducted under maximum biological containment.
The WHO says approved vaccines and treatments exist only for Ebola virus. Vaccines and treatments for Sudan virus and Bundibugyo virus are under development. It says early intensive supportive care, including rehydration and treatment of symptoms, improves survival.
What past outbreaks show
According to the CDC, Ebola disease was first identified in 1976, following an outbreak in a place that is today the Democratic Republic of the Congo. It names Ebola virus, Sudan virus and Bundibugyo virus as the three viruses behind most large outbreaks in Africa. The CDC says up to 90% of Ebola virus cases are fatal without treatment, compared with about 50% for Sudan virus and about 30% for Bundibugyo virus. The WHO says the average case fatality rate is around 50%, and has ranged from 25% to 90% in past outbreaks.
The CDC describes how specific measures worked in particular outbreaks. In the 1995 outbreak in Kikwit, it says, spread within health care settings was halted almost immediately once face masks, gloves and gowns were used. In 2011 in Uganda, it lists three factors that helped limit spread: clinical staff who suspected hemorrhagic fever from the start, correct use of protective equipment, and rapid laboratory confirmation within the country. In the West Africa epidemic of 2014 to 2016, the CDC says, quickly identifying and monitoring all contacts of infected travelers prevented broader outbreaks in Mali and Senegal. In Nigeria, a rapid response confined the outbreak to two cities.
The CDC also points to the role of communication. It says radio broadcasts were used during an outbreak in Kasai Occidental Province in the Democratic Republic of the Congo to share messages on how Ebola spreads and how to prevent it. In the Republic of the Congo, it says, meetings were held for women, who are usually the primary caretakers of patients. For one 2021 outbreak in the Democratic Republic of the Congo, the CDC says the outbreak was declared over 42 days after the last confirmed patient was released from treatment.
The CDC says genetic sequencing linked several later outbreaks to earlier ones. These included outbreaks in 2021 in the Democratic Republic of the Congo and in Guinea, which it says were likely caused by persistent infection in a survivor rather than a fresh spillover from animals.