Transmission Routes
Ebola has well-established transmission routes. Understanding both how it spreads and how it does not spread prevents unnecessary panic and focuses protective action.
- Direct contact with blood or body fluids (vomit, feces, urine, saliva, sweat, breast milk, semen) of a person who is sick with or has died from Ebola
- Contact with contaminated objects — needles, syringes, bedding, or clothing that has been in contact with infectious body fluids
- Funeral and burial practices involving direct contact with the deceased — a major transmission route in past West Africa outbreaks
- Contact with infected animals — fruit bats (the likely natural reservoir), non-human primates, or other infected wildlife
- Sexual transmission — the virus can persist in semen for many months after recovery; RNA has been detected up to 18 months after discharge and transmission documented up to 15 months (see below)
- Airborne transmission — Ebola does not spread through the air or via respiratory droplets under normal conditions
- Food or water — Ebola is not transmitted through food or water supplies
- Mosquitoes or insects — Ebola is not a vector-borne disease
- Casual contact — passing someone on the street, sitting in the same room, or brief social contact does not transmit Ebola
- Contact before symptoms appear — a person is not infectious until they develop symptoms
How Contagious Is Ebola? The Measured Numbers
"Spreads by direct contact" describes the route. The reproduction number, serial interval and time-to-isolation describe the speed — and they explain why contact tracing can stop it.
| Parameter | Estimate (95% CI) | Source and setting |
|---|---|---|
| Basic reproduction number R0, Guinea 2014 | 1.71 (1.44–2.01) | WHO Ebola Response Team, NEJM 2014 — Ebola (Zaire) virus, from the initial exponential-growth period |
| R0, Liberia 2014 | 1.83 (1.72–1.94) | |
| R0, Sierra Leone 2014 | 2.02 (1.79–2.26) | |
| Mean serial interval (onset to onset in the next case) | 15.3 days (SD 9.3) | WHO Ebola Response Team, NEJM 2014 |
| Mean time from symptom onset to hospitalisation | 5.0 days (SD 4.7) | Same — "a measure of the period of infectiousness in the community"; maximum over 40 days |
| R0, DRC 2026 (Bundibugyo virus) | 1.4–2.1 (central 1.71) | Olwit et al., 2026 — a narrative review of early-outbreak estimates, not a primary analysis; treat as provisional |
These are Zaire-virus figures from 2014 except the last row. No peer-reviewed transmission parameters specific to Bundibugyo virus in 2026 had been published as of September 14, 2026; WHO's Disease Outbreak News gives the incubation period as 2–21 days and states that "infected individuals are not infectious until symptom onset," the same as for Zaire virus.
Who Transmits Most — from 129 Chains of Transmission
Robert et al. (American Journal of Epidemiology 2019) reconstructed 129 transmission chains covering 860 cases in the later phase of the Guinea epidemic and modelled how many secondary cases each person generated. The findings, with their confidence intervals:
- Unsafe burial: 1.82 times as many secondary cases (IRR 1.82, 95% CI 1.10–3.02).
- Being treated in an Ebola treatment unit (among patients who died): 38% fewer secondary cases (IRR 0.62, 95% CI 0.38–0.99).
- Children transmitted least (IRR 0.35, 95% CI 0.21–0.57, versus adults); older adults transmitted most.
- Men transmitted somewhat less than women (IRR 0.71, 95% CI 0.55–0.93) — consistent with women doing more caregiving and body preparation.
- The first generation of each chain averaged 1.77 secondary cases; later generations 0.70 — once a chain is recognised, control measures cut transmission below the replacement level.
The same pattern appears in the only Bundibugyo transmission study before 2026: in Uganda in 2007, most transmission was associated with handling the dead without protection, adjusted odds ratio 3.83 (95% CI 1.78–8.23; Wamala et al., Emerging Infectious Diseases 2010).
What the 2026 Outbreak Has Shown About Transmission So Far
- Exposure in Uganda's 21 cases (CDC MMWR 2026;75(35):551): 14 of 20 confirmed patients were infected in DRC and travelled into Uganda while symptomatic, most seeking care; four Ugandan health workers were infected during an attempted resuscitation of a probable case who died and was embalmed before testing; one driver was infected through contact with a body. Every Ugandan-acquired infection came from a sick or dead person, not from casual contact.
- Health-worker share: 7.2% of confirmed DRC cases and 20% of Uganda's, per the Olwit et al. review of early reports; WHO's counts rose from 102 health-worker infections (July 1) to at least 155 (August 9), then stopped being restated in WHO's September reports.
- Chains unrecognised: CDC's operational review found that only 15–20% of new DRC cases had been previously identified as contacts, against a target above 90% — most transmission is occurring outside known chains (CDC MMWR 2026;75(35):554).
- Exported cases: one to France (a physician who self-reported symptoms on arrival at Paris–Charles de Gaulle on June 23, 2026; no secondary cases among five flight contacts and 107 contacts in Kinshasa) and two U.S. citizens evacuated to Germany, with no onward transmission reported (WHO DON 612–616).
Animal-to-Human Spillover
Every Ebola outbreak begins with a spillover event — when the virus jumps from its animal reservoir into a human.
The Bat Reservoir
The natural reservoir of Ebola virus is believed to be fruit bats, particularly species in the family Pteropodidae (Old World fruit bats). The virus appears to circulate in bat populations without causing disease in the bats themselves — a common pattern in zoonotic viruses.
Human outbreaks typically begin when a person comes into contact with an infected animal. This can occur through:
- Handling or butchering infected bats or primates for bushmeat
- Entering caves or forests where infected bats roost
- Contact with a sick non-human primate (gorilla, chimpanzee) that was itself infected by bats
Once the virus enters a human, it spreads person-to-person through direct contact, not through further animal contact.
Frequently Asked Questions
Is Ebola airborne?
No. Ebola does not spread through the air under normal conditions. The CDC, WHO, and all major infectious disease organizations are unequivocal on this point. Transmission requires direct contact with infected body fluids. This misconception causes unnecessary panic and discriminatory treatment of people from affected regions.
Note: In extremely rare experimental conditions involving aerosols, some studies have shown airborne transmission in non-human primates — but this has never been documented in real-world human outbreaks and requires conditions not present in normal human contact.
Can you get Ebola from a survivor?
Yes, in limited ways. While Ebola survivors are no longer contagious through casual contact once recovered, the virus can persist in "immune-privileged" sites — the testicles, the inside of the eye and the brain, per WHO — for extended periods. The two largest cohorts, both from Sierra Leone, give the actual curve. Deen et al. (NEJM 2017) tested 210 male survivors: RNA was present in all 7 men sampled within 3 months of discharge, 26 of 42 (62%) at 4–6 months, 15 of 60 (25%) at 7–9 months, 4 of 26 (15%) at 10–12 months, 4 of 38 (11%) at 13–15 months, 1 of 25 (4%) at 16–18 months, and none at 19 months or later. Thorson et al. (PLoS Medicine 2021), following 220 men every two weeks, put the positive rate at 75.4% (95% CI 66.9–82.0) six months after discharge, a median clearance time of 204 days, 26.8% at nine months and 6.0% (95% CI 3.1–10.2) at one year — and above 20% at one year among men over 35 who had severe acute disease. One survivor's persistent seminal virus caused a new cluster in Guinea and Liberia in 2016, about 470 days after his illness, with virus detected 531 days after onset (Diallo et al., Clinical Infectious Diseases 2016).[4]
WHO's guidance follows from this: offer male survivors monthly semen testing until two consecutive negative results, and where no testing programme exists, practise safer sex for 12 months (WHO fact sheet, May 2026). CDC's 2015 advice, after the first probable sexual transmission in Liberia, is still the operative caution: avoid contact with a male survivor's semen until testing shows the virus is gone. A limitation both cohorts state: detecting RNA is not the same as proving infectiousness, which was not directly measured.
Why are funerals such a major transmission risk?
Ebola-infected bodies remain contagious after death — and viral loads in body fluids can be extremely high in the final stages of illness. Traditional funeral and burial practices in many affected communities in sub-Saharan Africa involve washing and touching the body of the deceased, creating direct contact with highly infectious fluids. During the 2014–16 West Africa epidemic, the WHO linked a large share of cases to traditional burial and funeral practices — an estimated 60% of cases in Guinea and up to 80% in Sierra Leone at points during the outbreak.[5]
What Is Not Known
- Whether Bundibugyo virus transmits differently from Zaire virus. Its incubation period (mean 11.3 days in 2012; Kratz et al.) and route are the same; no 2026-specific serial interval or reproduction number has been published in a peer-reviewed primary analysis.
- How long Bundibugyo virus persists in survivors' semen. Every persistence cohort above studied Zaire-virus survivors. With more than 1,600 recovered patients in the 2026 outbreak (WHO DON 617), this will be answerable — it has not been answered.
- Whether detectable RNA equals infectiousness, and at what level. Both Sierra Leone cohorts say so explicitly.
Compared to what? For how Ebola's exposure and transmission compare with 14 other viruses, see the Virus Risk Perspective and this site's Ebola risk perspective.
Sources & References
- Centers for Disease Control and Prevention. How Ebola Disease Spreads. Page dated June 2, 2026. cdc.gov/ebola/causes
- World Health Organization. Ebola disease — fact sheet. Updated May 2026. who.int/news-room/fact-sheets/detail/ebola-disease
- WHO Ebola Response Team. Ebola virus disease in West Africa — the first 9 months of the epidemic and forward projections. N Engl J Med 2014;371:1481–95. doi:10.1056/NEJMoa1411100
- Robert A, et al. Determinants of Transmission Risk During the Late Stage of the West African Ebola Epidemic. Am J Epidemiol 2019;188(7):1319–1327. doi:10.1093/aje/kwz090
- Wamala JF, et al. Ebola hemorrhagic fever associated with novel virus strain, Uganda, 2007–2008. Emerg Infect Dis 2010;16(7):1087–92. doi:10.3201/eid1607.091525
- Deen GF, et al. Ebola RNA Persistence in Semen of Ebola Virus Disease Survivors — Final Report. N Engl J Med 2017;377:1428–37. doi:10.1056/NEJMoa1511410
- Thorson AE, et al. Persistence of Ebola virus in semen among Ebola virus disease survivors in Sierra Leone: A cohort study of frequency, duration, and risk factors. PLoS Med 2021;18(2):e1003273. doi:10.1371/journal.pmed.1003273
- Diallo B, et al. Resurgence of Ebola Virus Disease in Guinea Linked to a Survivor With Virus Persistence in Seminal Fluid for More Than 500 Days. Clin Infect Dis 2016;63(10):1353–1356. doi:10.1093/cid/ciw601
- Christie A, et al. Possible Sexual Transmission of Ebola Virus — Liberia, 2015. MMWR 2015;64(17):479–81. PMID 25950255
- Mutegeki M, et al. Notes from the Field: Clinical Characteristics of Patients with Ebola Disease Caused by Bundibugyo Virus — Uganda, 2026. MMWR 2026;75(35):551–553. doi:10.15585/mmwr.mm7535a2
- Kabasele D, et al. Notes from the Field: Characteristics and Monitoring of the 2026 Outbreak of Ebola Disease Caused by Bundibugyo Virus — DRC, August 2026. MMWR 2026;75(35):554–556. doi:10.15585/mmwr.mm7535e1
- Kilmarx PH, et al. Ebola virus disease in health care workers — Sierra Leone, 2014. MMWR 2014;63(49):1168–71. PMID 25503921
- Olwit G, et al. The Re-Emergence of Bundibugyo Ebolavirus in Uganda and the Democratic Republic of Congo: a narrative review. Infect Drug Resist 2026;19:632723. doi:10.2147/IDR.S632723
- Kratz T, et al. Ebola Virus Disease Outbreak in Isiro, DRC, 2012: Signs and Symptoms, Management and Outcomes. PLoS One 2015;10(6):e0129333. doi:10.1371/journal.pone.0129333
- World Health Organization. Disease Outbreak News 612–617 (July–September 2026): Ebola disease caused by Bundibugyo virus. who.int/…/2026-DON617
- Goldstein T, et al. The discovery of Bombali virus adds further support for bats as hosts of ebolaviruses. Nat Microbiol 2018;3:1084–1089. PMID 30150734
- World Health Organization. Factors that contributed to undetected spread of the Ebola virus and impeded rapid containment (One year into the Ebola epidemic, 2015). who.int
