Lancet study also suggests that virus was transmitting six weeks before outbreak was officially declared by health officials
A rare strain of Ebola detected in Democratic Republic of Congo (DRC) has now confirmed transmission in Uganda, and is potentially on course to reach South Sudan, according to the World Health Organization (WHO).
The deadly Bundibugyo ebolavirus, of which there is no licenced vaccine to help prevent, has a 70 per cent chance of reaching South Sudan, experts said.
In a study published in The Lancet Infectious Diseases, they advise that neighbouring countries should implement public health measures now, such as border surveillance, contact tracing and safe burial practices, in order to limit further transmission.
The current Ebola outbreak was officially declared on May 15, with WHO declaring a public health emergency of international concern two days later – the highest level of international health alert.
However, according to the study, retrospective investigations indicate that transmission began in early April 2026. The six-week delay between the estimated first case and official confirmation suggests the virus was spreading undetected through communities, in a region already destabilised by conflict, displacement, and limited healthcare access.
As of June 22, more than 1,000 laboratory-confirmed cases and 267 confirmed deaths have been recorded across affected health zones in the DRC as a result of the current Ebola outbreak.
In their study WHO officials said that uncertainty remains around reported case numbers due to low rates of contact tracing.
The authors wrote: “Sustained control nonetheless remains the primary determinant of regional risk: importation into Uganda is already established, and South Sudan must continue to reinforce infection prevention and control, rapid response capacity, and cross-border surveillance under International Health Regulations 2005.”
Uganda has reported 20 confirmed cases and two deaths from the outbreak so far, including five infections among healthcare workers. Some of these cases were brought across the border from the DRC, while others were caught locally from those individuals.
The authors note that Uganda has been able to identify and respond to cases quickly, drawing on its experience managing previous Ebola outbreaks and the public health systems it has built up over many years.
The researchers now identify South Sudan as the most urgent preparedness priority, estimating a nearly seven-in-ten chance that at least one case will arrive there within the 12-week modelling timeline.
South Sudan also has some of the weakest public health infrastructure in the region, with known gaps in case management, contact tracing, safe burial and border surveillance.
Rwanda (8.6 per cent) and Burundi (2.0 per cent) remain at comparatively low risk. However, the study authors note that the risk can still increase depending on detection capacity, travel patterns, and the speed of each country’s response systems.
Bundibugyo ebolavirus is one of several strains of the Ebola virus. It was first identified during a 2007 outbreak in western Uganda and caused a second outbreak in the DRC in 2012.
Compared to the more familiar Zaire strain, which was responsible for the 2014–2016 West African epidemic, the Bundibugyo strain tends to have a slightly lower mortality rate and is less transmissible.
However, it still causes severe haemorrhagic fever, kills a significant proportion of those infected, and spreads through direct contact with the bodily fluids of sick or deceased people.
This week France confirmed its first case of Ebola resulting from the current outbreak, with a doctor found to have been infected after returning from a humanitarian mission in the DRC.
The French Health Ministry said the doctor was ‘immediately admitted to a specialised facility’ and is in a stable condition. They stressed that the risk to the population was ‘very low’.
Ireland’s Health Protection and Surveillance Centre said that Ireland has prior experience of managing Ebola-related preparedness as part of international public health collaboration.
“There are established High Consequence Infectious Diseases (HCIDs) clinical pathways, including isolation, infection prevention and control (IPC) and transfer protocols remain in place and are under continuous review,” the organisation said in a statement.
“Ireland is well prepared to manage an imported case of Ebola, should this occur. However, the current risk level remains low and there are robust surveillance systems, international coordination, and HCID preparedness measures in place to ensure an effective response if needed.”
Read the study: Size of the 2026 Ebola outbreak and risk of cross-border spillover from Bundibugyo virus in Ituri Province, DR Congo, and its implications for preparedness: a recalibrated stochastic modelling study – The Lancet Infectious Diseases.