Ebola disease caused by Bundibugyo virus

Disease caused by Bundibugyo virus, an orthoebolavirus pathogenic to humans.

Last updated on 30 September 2026

Epidemiology

Ebola disease caused by Bundibugyo virus was first identified in 2007 in Bundibugyo District, western Uganda. The outbreak, which probably began in August 2007 and continued until January 2008, resulted in 56 confirmed cases and 37 deaths, with a case fatality rate of 24.8%.¹

A second outbreak was reported in August 2012 in the Isiro region, in the north-east of the Democratic Republic of the Congo, approximately 400 km north-west of Bundibugyo.¹˒² A total of 36 confirmed cases were reported. This outbreak caused 34 deaths, and the case fatality rate reached 54.8%.¹

Genomic and epidemiological analyses suggested that this outbreak had a zoonotic origin independent of the 2007 outbreak in Uganda.¹

An outbreak with high mortality has been ongoing in the Democratic Republic of the Congo (DRC) and Uganda since May 2026.

According to WHO, as of 1 August 2026, 3,626 confirmed cases had been reported (3,605 in the DRC, 20 in Uganda and one in France), with 1,589 deaths, including two in Uganda. As of 30 July, at least 654 patients had recovered: 651 in the DRC and 18 in Uganda locally, as well as three patients treated outside the outbreak area who had recovered (two in the United States repatriated to Germany, and one in France).³ The imported case in France involved a humanitarian doctor returning from a mission in an area with active virus circulation in the DRC, who received care immediately upon arrival in the country.

This is now the largest Ebola virus disease outbreak ever recorded in the DRC, surpassing the 2018–2020 outbreak, which resulted in 3,317 confirmed cases.³

The case fatality rate of Ebola disease caused by Bundibugyo virus ranges from approximately 25% to 36%, substantially lower than that of Ebola Zaire (60–90%).⁴ However, mortality varies between outbreaks depending on the speed of detection and isolation, access to supportive care (hydration, intensive monitoring, etc.), the strength of health systems and the outbreak response, as well as community involvement and adherence to control measures.⁴

These outbreaks established that Bundibugyo virus is an orthoebolavirus pathogenic to humans and capable of sustained human-to-human transmission.¹

Virus

Bundibugyo virus (BDBV) belongs to the genus Orthoebolavirus. It is genetically and antigenically distinct from Ebola virus and Sudan virus.¹ These differences are particularly marked in the glycoprotein, the main antigenic target of many vaccines and monoclonal antibodies.¹

Transmission

Bundibugyo virus is a zoonotic pathogen. Fruit bats of the family Pteropodidae are its main natural reservoir. Cross-species transmission may occur through human interactions with infected wildlife, particularly bats and non-human primates.⁴

Animal-to-human transmission

Transmission occurs through direct contact with the blood, tissues or bodily fluids of infected animals during hunting, slaughter or consumption of bushmeat.⁴

Human-to-human transmission

Transmission occurs primarily through direct contact with infectious bodily fluids, including blood, vomit, faeces, urine, saliva, breast milk and semen. It can also occur through:⁴

  • Contaminated objects, such as bedding and medical equipment.
  • Unsafe healthcare practices, such as reusing needles.
  • Traditional funeral practices involving contact with the deceased.

The risk of transmission increases considerably in the advanced stages of the disease, when viral load is highest, and remains high when handling bodies after death.⁴

Diagnosis and symptoms

The disease is generally diagnosed using RT-PCR or serology (ELISA testing), which is useful in the later stages or for retrospective diagnosis.⁴

The clinical presentation of BDBV disease is broadly similar to that of other forms of Ebola virus disease, although the clinical features specific to this species remain insufficiently characterised.¹

The incubation period ranges from 2 to 21 days, after which infected people generally develop fever, fatigue, headaches, muscle pain and gastrointestinal symptoms, including nausea, vomiting, abdominal pain and diarrhoea.¹ People are not infectious during the incubation period.⁴

Difficulty breathing, difficulty swallowing and loss of appetite are also common, while haemorrhagic manifestations occur in only around 10% of people with laboratory-confirmed BDBV infection. This confirms that bleeding is neither consistently present nor required to establish the diagnosis.¹

Severe disease may progress to shock, altered mental status, acute kidney injury, liver failure, coagulopathy, respiratory failure and multiple organ failure.¹

Treatment and vaccination

There are currently no specific antiviral treatments approved for BDBV.¹˒⁴

Supportive care is therefore the cornerstone of treatment:¹˒⁴

  • Rehydration and correction of electrolyte imbalances to compensate for losses caused by vomiting and diarrhoea.
  • Haemodynamic management to maintain blood pressure and oxygenation.
  • Management of complications through blood transfusions or treatments to promote clotting in the event of bleeding.
  • Treatment of co-infections, such as malaria and bacterial infections.

Research avenues

  • Treatments

Among candidate drugs, MBP134 is the most advanced. This cocktail of two broad-spectrum monoclonal antibodies, capable of neutralising several viral species within the genus Orthoebolavirus, has already been tested in non-human primates.⁵˒⁶

A human clinical trial, PARTNERS (Platform Adaptive Randomised Trial for New and Repurposed Filovirus TreatmentS), is under way to evaluate MBP134 and remdesivir. This randomised controlled trial is funded by WHO and coordinated by INRB (DRC), the Institute of Tropical Medicine in Belgium and the University of Oxford, with support from Africa CDC, ALIMA and MSF.

The antiviral treatments are administered alone or in combination to determine whether they improve survival in patients with BDBV disease and whether combination therapy provides an additional benefit over either drug alone. These two treatments were selected by WHO’s Technical Advisory Group (TAG) following a review of preclinical evidence, safety data and lessons learned from previous outbreaks, in a context where no treatment is currently licensed for this disease and no drug has demonstrated consistent efficacy against all viruses responsible for Ebola disease. Designed as an adaptive platform trial, PARTNERS will be able to incorporate new treatments over time. It includes patients of all ages with confirmed Ebola disease caused by Bundibugyo virus, who are followed for at least 28 days. Enrolment of the first patients began in the DRC in early July 2026.⁷

  • Post-exposure prophylaxis

Obeldesivir and remdesivir, two broad-spectrum antivirals, have shown activity as post-exposure prophylaxis (PEP) against BDBV, although the evidence remains limited.¹

Since 14 July 2026, the EBO-PEP trial has been evaluating the investigational antiviral obeldesivir as PEP against Ebola disease caused by Bundibugyo ebolavirus (BDBV), under a subprotocol entitled EBO-PEP ODV-BDBV.

  • Vaccination

On 3 July 2026, the Coalition for Epidemic Preparedness Innovations (CEPI) activated its highest level of response to the Ebola outbreak caused by BDBV. It adopted a portfolio approach, funding three distinct vaccine platforms in parallel to maximise the likelihood and speed of developing an effective candidate.

The three approaches are based on technologies already validated for other filoviruses (Ebola Zaire, Sudan and Marburg):

  • An rVSV viral vector (vesicular stomatitis virus): this research approach uses the same platform as the licensed Ebola Zaire vaccine, drawing on the strongest preclinical evidence, although it has not yet been tested in humans for Bundibugyo.
  • A ChAdOx viral vector: this approach uses the technology of the Oxford/AstraZeneca COVID-19 vaccine, offering an advantage in manufacturing speed. However, preclinical data on Ebola Bundibugyo remain limited.
  • An mRNA platform: this uses the technology employed in COVID-19 vaccines. Development could be very rapid, but BDBV-specific data are also limited.

Two phase I clinical trials based on these platforms have already been launched.

The University of Oxford’s ChAdOx1 BDBV candidate (BD-Ebov trial, 50 volunteers, doses manufactured by the Serum Institute of India) was the first to move forward, with the first dose administered on 24 July 2026.⁸ It was followed on 4 August 2026 by Moderna’s mRNA candidate, mRNA-1469, whose first dose was administered in a trial conducted at three sites in Canada involving approximately 80 volunteers.⁹

CEPI is also supporting two additional rVSV candidates (IAVI/Hilleman Laboratories and Public Health Vaccines) and continues to explore other vaccine options.¹⁰

Research activities of ANRS MIE on Ebola disease caused by Bundibugyo virus and filoviruses

Leadership of the CORC on filoviruses

In early 2025, ANRS MIE was appointed to lead the Collaborative Open Research Consortium (CORC) on filoviruses. The agency has become a WHO Collaborating Centre.

Activation of an Outbreak Response unit

In March 2025, the ANRS MIE “Epidemic Monitoring and Response” division activated a level 1 Outbreak Response unit on filoviruses.

Coordinated action on viral haemorrhagic fevers

The coordinated action on viral haemorrhagic fevers focuses particularly on scientific research on filoviruses. Its working groups address therapeutic approaches, vaccination and wildlife. The aim is to generate research projects through international collaborations, primarily with our partners in Africa.

EBO-PEP research project

ANRS MIE funds the EBO-PEP research project, a platform trial in preparation since 2024, coordinated by ALIMA and conducted by an international consortium that also includes the National Institute for Biomedical Research (INRB), Africa CDC and several academic and humanitarian partners.

EBO-PEP aims to evaluate different post-exposure prophylaxis (PEP) strategies in high-risk contacts of people with filovirus disease across several countries in sub-Saharan Africa (DRC, Uganda, Guinea, Liberia and Sierra Leone).

Open for enrolment since 14 July 2026 in Ituri (DRC), EBO-PEP is evaluating obeldesivir, an investigational oral antiviral developed by Gilead Sciences that has demonstrated preclinical efficacy against several filoviruses, including Bundibugyo virus. It is administered to adults and children older than 12 years who have had direct, high-risk contact with a confirmed case within the previous five days and have no symptoms. Daily follow-up lasts 21 days, with a final visit at 42 days.

A second component, involving compassionate use, provides for the administration of remdesivir to children younger than 12 years and pregnant or breastfeeding women who have had high-risk contact, owing to insufficient data on obeldesivir in these populations.

In the absence of an available vaccine against Bundibugyo virus, the aim is to establish a post-exposure prevention strategy that would complement the management of patients who are already symptomatic and help curb transmission during the outbreak.

References

  1. Kuppalli K, et al. A review of Bundibugyo virus and the 2026 outbreak: lessons for epidemic preparedness. Lancet Infect Dis 2026:S1473-3099(26)00414-7.
  2. Burk R, et al. Neglected filoviruses. FEMS Microbiol Rev 2016;40(4):494–519.
  3. WHO: Ebola disease caused by Bundibugyo virus – Democratic Republic of the Congo (accessed 10 August 2026).
  4. Africa HealthKnowledge Hub: Bundibugyo virus disease fact sheet (accessed 10 August 2026).
  5. Bornholdt ZA, et al. A two-antibody pan-ebolavirus cocktail confers broad therapeutic protection in ferrets and nonhuman primates. Cell Host Microbe 2019;25:49–58.e5.
  6. Patel A & Weiner DB. It Takes a Matured mAb to Treat Ebolavirus Infection. Cell Host Microbe 2019;25:10–12.
  7. WHO: Patient enrolment begins in a scientific trial to identify the first effective treatments for Bundibugyo virus disease (accessed 10 August 2026).
  8. NIHR: University of Oxford launches trial of new Ebola vaccine (accessed 10 August 2026).
  9. CEPI: Moderna’s Bundibugyo ebolavirus vaccine candidate enters first human trial, backed by CEPI (accessed 10 August 2026).
  10. CEPI: Three vaccine designs in the race to contain Bundibugyo Ebola (accessed 10 August 2026).