What is Bundibugyo virus? The Ebola species with no vaccine

Bundibugyo virus (BDBV) is one of six known orthoebolaviruses, the group of viruses that cause Ebola disease. Three of them cause large outbreaks: Ebola virus (formerly called Zaire ebolavirus), Sudan virus, and Bundibugyo virus [9]. The illness caused by BDBV is called Bundibugyo virus disease (BVD). For a broader look at Ebola disease, see Ebola, Forgotten but Not Gone and Fighting Ebola: Breakthroughs, challenges, and the path forward.

They cause similar illness but are genetically very different. When scientists first sequenced Bundibugyo virus in 2007, its genome differed by more than 30% from every other known ebolavirus. Its surface glycoprotein, the part of the virus that vaccines and antibody drugs are built to target, differed from Zaire ebolavirus by more than 35% at the protein level [10].

Bundibugyo has historically been less lethal. CDC (the US Centers for Disease Control and Prevention) says it kills about 30% of people who get sick, versus up to 90% for untreated Zaire infections [11]. The current outbreak’s crude case fatality ratio is about 48% [1, 7].

Fruit bats are suspected to be the natural reservoir. People are first infected through close contact with the blood or secretions of infected wildlife, such as bats or nonhuman primates [1].

It then spreads between people through direct contact with the blood or other body fluids of someone who is sick or has died, or with contaminated materials like bedding and clothing [1, 9]. It does not spread like respiratory viruses such as flu or COVID-19, so people cannot catch it simply by being near someone [12]. People are not infectious until symptoms begin [1].

Spread is amplified in health facilities with weak infection control and at burials that involve touching the body [1]. Ebola viruses can also persist in semen; for Zaire ebolavirus, sexual transmission has been documented up to 15 months after recovery [9].

Bundibugyo virus was first identified in November 2007 during a hemorrhagic fever outbreak in Bundibugyo District, western Uganda. Samples tested negative on real-time RT-PCR assays designed to detect all known Zaire and Sudan ebolaviruses and marburgviruses, and CDC scientists went on to identify a new species [10]. CDC records 131 cases and 42 deaths (32%) in that outbreak [11].

The second outbreak came in 2012 in Orientale Province, northeastern DRC, with 62 cases and 34 deaths, according to CDC [11]. WHO puts the case fatality rates of the 2007 and 2012 outbreaks at 30% and 50% [1].

The 2026 outbreak

The DRC declared its 17th Ebola outbreak in May 2026, in Ituri Province [6, 13]. On May 17, WHO declared a public health emergency of international concern, when Ituri had eight confirmed and 246 suspected cases and Kampala, Uganda, had two confirmed cases [13].

It has spread faster than previous Ebola outbreaks, passing 1,000 confirmed cases within 40 days of the response starting. The 2018 DRC outbreak took about 235 days to reach that mark [6].

As of October 20, 2026 (situation report published October 21), the DRC had reported [7]:

• 9,704 confirmed cases and 4,687 deaths
• 2,595 recoveries
• Cases in 66 of 178 health zones across eight provinces

Ituri remains the epicentre, with 7,040 cases, followed by North Kivu with 2,146. Nord-Ubangi, which borders the Central African Republic, became the eighth affected province in mid-October [5, 7].

Outside the DRC, Uganda reported 20 confirmed cases and two deaths before declaring its outbreak over in August, and France reported one case [14, 15]. Kenya’s nine cases all belong to the cluster linked to its first patient [6]. On October 20, Nigeria confirmed an imported case in Abuja, a woman who had arrived from Uganda on October 3 [16, 17]. Responders infected in the DRC have also been medically evacuated to Germany (two patients) and the Netherlands (one), and an aid worker was evacuated to the UK for monitoring after a possible exposure. Evacuated cases are counted in the DRC’s total, not as local cases [1, 18, 19].

Symptoms appear 2 to 21 days after exposure [1]. Early symptoms are nonspecific:

• Fever
• Fatigue
• Muscle pain
• Headache
• Sore throat

These can be followed by vomiting, diarrhea, abdominal pain, rash, and signs of kidney and liver damage. Despite its reputation, bleeding is less common and tends to occur later in the illness [9].

Early BVD resembles common illnesses such as malaria and typhoid fever, so laboratory testing is essential [1, 9]. Confirmation is usually by RT-PCR, which detects viral genetic material; antigen tests, antibody tests, and virus culture are also used [9].

Travel history matters: doctors in Nairobi suspected a viral hemorrhagic fever based on the first patient’s symptoms and travel [2]. The species matters too. In 2007, assays designed for other ebolaviruses initially missed Bundibugyo [10].

There is no approved treatment for BVD. Care is supportive: fluids, electrolyte replacement, oxygen, blood pressure management, and pain control. Early supportive care improves survival [9, 20].

Why Ebola vaccines and drugs don’t cover Bundibugyo

The US FDA approved the Ervebo vaccine in 2019 to prevent disease caused by Zaire ebolavirus [21], and two monoclonal antibody treatments, Inmazeb and Ebanga, in 2020 for Zaire infection [22]. Ebanga, for example, is directed at the Zaire virus’s glycoprotein, and its label states that its efficacy has not been established for other orthoebolavirus species [23]. Because Bundibugyo’s glycoprotein differs by more than a third [10], these products cannot be assumed to work against it.

Candidate treatments

In July 2026, the WHO-sponsored PARTNERS trial began enrolling patients in the DRC. It is testing a monoclonal antibody (MBP134) and the antiviral remdesivir, alone and in combination [20].

With no Bundibugyo-specific vaccine ready, WHO advisers recommended testing Ervebo in a Phase 3 study [24]. In August, 70,000 doses were released to the DRC for a trial and for frontline workers. WHO says it is not known whether Ervebo protects against Bundibugyo in humans, though early laboratory and animal data suggest some protection [25]. A study of Ervebo in 20,000 frontline workers began on September 19 [26].

Bundibugyo-specific vaccines are in early human trials. The University of Oxford’s ChAdOx1 BDBV vaccine launched a Phase 1 trial in the UK in July and began a Phase 1 trial in Uganda on October 6. The Serum Institute of India has stockpiled about 620,000 doses for potential future use [15, 27]. A Phase 1 trial of Moderna’s mRNA-1469 began in Canada on August 3, when the first participant was dosed in Truro, Nova Scotia [28]. None has been approved.

Without a proven vaccine, prevention means avoiding contact with the body fluids of sick or deceased people. Outbreak control relies on isolating patients, monitoring contacts for 21 days, safe and dignified burials, and strict infection control in health facilities, where workers need extra protection when caring for suspected cases. In affected areas, people should also avoid bats, monkeys, apes, and their raw meat [9, 29].

As of October 19, 2026, US CDC’s travel health notices are [30]:

• Level 4 (avoid all travel): Ituri and Nord-Kivu provinces, DRC
• Level 3 (reconsider nonessential travel): Haut-Uélé and Tshopo provinces, DRC
• Level 2 (enhanced precautions): Uganda and other DRC provinces
• Level 1 (usual precautions): Kenya

The US has also temporarily restricted entry: travelers who have been in the DRC within 21 days cannot board commercial flights to the United States [29]. WHO advises against travel and trade restrictions [1]. The Kenyan cluster is a reminder of how global travel affects the spread of infectious disease.

Those who must travel should avoid sick people, health facilities, traditional healers, funerals that involve touching the body, and caves or mines where bats live [29].

After leaving the DRC, Uganda, or South Sudan, travelers should watch for symptoms for 21 days. Anyone who develops fever or other symptoms should isolate and call a health department or doctor before going in, and mention their travel history [31]. For more on talking to your doctor after a trip, see Fever after travel? Here’s what to tell your doctor and why it matters.

Bundibugyo virus was discovered in 2007 and had caused only two known outbreaks before 2026. It is now driving the second-largest Ebola epidemic on record, with cases in eight DRC provinces and a linked cluster in Kenya.

The vaccine and treatments that transformed the response to Zaire ebolavirus were not designed for this species. Trials are under way, but for now, early detection, isolation, supportive care, contact tracing, and safe burials remain the main defences. Figures change daily, so check WHO, CDC, and national health ministries for the latest.

GIDEON is one of the most comprehensive global databases for infectious diseases. Data is refreshed daily, and GIDEON tracks outbreaks and case data for every country, including past Ebola outbreaks by virus species. Whether your work involves quantifying data, learning about specific microbes, or testing differential diagnosis tools, GIDEON has you covered.