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Scientists comment on the genomes of the Bundibugyo virus from the Ebola outbreak in the DRC and Uganda.
Dr Daniela Manno, Clinical Assistant Professor at the London School of Hygiene & Tropical Medicine (LSHTM), said:
Why is it important to sequence the genomes of the samples?
“Sequencing the viral genomes is important because it helps confirm exactly which virus is causing the outbreak and allows scientists to compare the virus with strains identified in previous outbreaks.
“It also provides valuable information on how cases may be linked epidemiologically and how the spillover event may have occurred — for example, whether transmission is likely occurring through sustained human-to-human spread following a single spillover event, or whether there may have been multiple independent introductions from an animal reservoir infecting humans or intermediate hosts over several episodes.
“This is particularly relevant in regions where people may have contact with wildlife reservoirs or environments such as caves or mining areas that may facilitate spillover events.”
What information can it tell us and how can it help in combating the outbreak?
“Genomic sequencing can support outbreak investigations by helping reconstruct transmission chains when combined with epidemiological investigations and contact tracing data. For example, it can help identify whether transmission is being amplified through healthcare-associated (nosocomial) spread, traditional funeral practices, or other high-risk exposure settings. This helps public health teams better understand what is driving transmission within affected communities and where interventions should be prioritised.
“It can also help monitor whether significant genetic changes are emerging over time that could potentially affect diagnostics, therapeutics, or vaccine performance.
Importantly, sequencing also helps researchers assess how genetically similar Bundibugyo virus is to other Ebola virus species for which vaccines and therapeutics already exist. This can provide clues about whether existing vaccines or monoclonal antibodies might provide some degree of cross-protection, while also helping guide the development of new vaccines and therapeutics that could potentially be used as part of outbreak control strategies.
Is there anything that we can see in this data that is novel or unusual in the genomes?
“At first glance, the phylogenetic analysis currently suggests that the 2026 outbreak viruses cluster together but are genetically distinct from viruses identified during the previous Bundibugyo outbreaks in 2007 and 2012. This supports the interpretation that the current outbreak is likely linked to a new spillover event from an animal reservoir, rather than persistence within human populations of viruses from earlier outbreaks.
“Interpretation of genomic findings should nevertheless always be done cautiously and alongside clinical and epidemiological data.”
Any other comments?
“One particularly important operational finding from the current outbreak is that rapid diagnostic assays targeting Zaire ebolavirus were initially negative, while broader pan-filovirus PCR assays detected the infection. This highlights the importance of maintaining broad diagnostic capacity for rarer filoviruses and not focusing preparedness only on the most common Ebola virus species.
“Another important point is that laboratories in DRC and Uganda were able to generate near-complete genomes within hours to days of confirmation, which is actually a positive sign of how much genomic surveillance capacity within affected countries has improved since earlier Ebola outbreaks.
“Rapid sharing of genomic data during outbreaks is extremely valuable for the global scientific and public health community. It allows researchers and response agencies around the world to rapidly analyse the virus, support diagnostic, therapeutic, and vaccine development, monitor viral evolution, and inform outbreak response strategies in near real time.”
Prof Aris Katzourakis, Professor of Evolution and Genomics, University of Oxford, said:
“Sequencing the genomes of an ongoing outbreak like the May 2026 Budinbugyo outbreak in the DRC is important, because the sequences can contain epidemiological and evolutionary signatures. The authors used genome sequence data to place the virus in an evolutionary context in order to understand whether for example this could be a new spillover. Importantly, the samples from this outbreak initially tested negative for Ebola using a Zaire-specific GeneXpert. However, pan-filovirus PCR and sequencing found the rarer Bundibugyo (BDBV) form of the virus, for which unfortunately there are fewer treatments and countermeasures. The team were able to analyse the three newly generated BDBV genomes from Uganda and the DRC in the context of 34 existing genomes from the previous outbreaks in 2007 and 2012. The tree was revealing in terms of the ongoing transmission of the virus, with the genome sequences clustering robustly in the phylogenetic tree, suggesting epidemiological linkage between Uganda and Bunia in the DRC. Thus there was likely a single original new spillover followed by transmission within and between countries. This highlights both the importance of rapid genome sequencing, public deposition and access to viral sequence data, and ongoing surveillance, in order to understand the spread of this virus within and between national borders. This is clearly going to have serious public health impacts, and further surveillance will be important for containing this public health emergency of international concern.”
Prof David Matthews, Professor of Virology, University of Bristol, said:
“This is a valuable rapid insight into the current outbreak, and it supports the initial finding that Bundibugyo virus is the cause. This is important because Bundibugyo virus disease has only caused two known outbreaks before, one in Uganda in 2007 and in 2012 in DRC. The Virological analysis reports that the initial genomes are consistent with a new spillover event by a Bundibugyo ebolavirus that is similar but distinct from these previous outbreaks.
“Genomic sequencing is valuable because it helps establish whether the outbreak is likely to have arisen from a single spillover event, followed by human-to-human transmission, or whether there may have been multiple separate introductions from an animal reservoir. The current dataset is still very preliminary, but so far it appears most consistent with a single recent introduction followed by onward person to person spread. That is useful because it suggests this outbreak can potentially be traced and interrupted as it has been in the past. Repeated independent spillovers from an animal source would complicate the efforts to stop the outbreak.
“Confirming this is not Zaire ebolavirus also has practical consequences: the licensed Ebola vaccine most often used in recent outbreaks is matched to Zaire ebolavirus and should not be assumed to protect well against Bundibugyo virus. This reinforces the need to speed up work on Bundibugyo-specific vaccines and other countermeasures.
“Further sequencing will also help make sure that any vaccine or antibody-based countermeasure in development will be closely matched to the virus causing this outbreak. As such it will be important to monitor the current outbreak virus directly rather than relying only on older reference sequences.
“Finally, genomic data can help work out how the virus is spreading. For example, if viruses found in different patients or locations are very similar or identical, that supports a recent link between the two individuals which can help investigators identify transmission chains that may otherwise be missed. In this way, sequencing complements contact tracing and can help inform public health advice that helps people to understand how to limit the spread of the virus. So, it can help confirm whether the usual Ebola control measures are successful or need adapting. With more data from more patients over time it can also help epidemiologists work out when the likely spillover event first occurred.
“We saw the value of this kind of rapid sequencing during the COVID-19 pandemic, where sequencing was used to track the emergence and spread of new variants and to monitor whether vaccines, diagnostics or treatments might need updating.”
Dr Charlotte Houldcroft, Assistant Professor of Virus Genomics, University of Cambridge, said:
Why is it important to sequence the genomes of the samples?
“Having genome sequences available from the emerging Bundibugyo virus outbreak is vital to help us develop rapid diagnostic tests specific to this type of Ebola. Genome sequences will already be informing vaccine work, as vaccine candidates for Bundibugyo virus have been tested in animals in the past, but we need to know if those vaccines are still a good match to the current outbreak strain.
What information can it tell us and how can it help in combating the outbreak?
“Genome sequences were really powerful in the 2014-2016 West African Ebola outbreak: they helped public health teams track, and most importantly break, transmission chains. Genome sequences were also useful for understanding very rare cases of survivors who may harbour persistent Ebola virus which is not cleared from the body and that can kick off new chains of transmission. We also want to identify, if possible, where this Bundibugyo virus outbreak originated: did it come directly from a wild animal, or has the outbreak been smouldering in humans for longer than currently realised?
Is there anything that we can see in this data that is novel or unusual in the genomes?
“Currently we have three new genomes, and they are broadly similar to the two previously known outbreaks (2007, 2012) but not direct descendants of either. This is consistent with the current Bundibugyo virus outbreak coming from an animal reservoir into humans – sometimes known as a spillover event; but we will likely need more genetic and epidemiological data to know how long this outbreak has been transmitting human to human.”
Prof Miles Carroll, Professor of Emerging Viruses, Pandemic Sciences Institute, University of Oxford, said:
“Using a method termed “molecular epidemiology”, rapid sample genome sequencing can enable scientists to understand who has infected who, as each sample will have a unique genetic signature. The relationship of these genetic signatures can help public health responders understand how the virus is spreading and lead to the shutdown of chains of transmission.
“Understanding how the virus is evolving is also important to ensure the current diagnostics will continue to be effective.
“It is essential that colleagues in DRC are provided with the essential scientific supplies to enable them to sequence rapidly and broadly to support molecular epidemiology. I imagine the initial target will be to sequence 500 samples ASAP.”
Initial genomes from May 2026 Bundibugyo Virus Disease Outbreak in the Democratic Republic of the Congo and Uganda
https://virological.org/t/initial-genomes-from-may-2026-bundibugyo-virus-disease-outbreak-in-the-democratic-republic-of-the-congo-and-uganda/1032
Declared interests
Prof Aris Katzourakis: “I have no conflicts of interest.”
Dr Charlotte Houldcroft: Charlotte Houldcroft’s group hosts a PhD student part-funded by Virothera, an immune therapeutics developer.
Prof Miles Carroll: No COI
Dr Daniela Manno: “I have previously worked on Ebola vaccine clinical trials and outbreak preparedness research, including studies funded by CEPI and other international research funders. I do not have any commercial interests related to Ebola vaccines or therapeutics.”
For all other experts, no reply to our request for DOIs was received.