Ebola Bundibugyo Virus — DRC
Spread Risk Assessment #4 · International Dissemination

Reports #1 to #3 quantified relative importation risk in the immediate cross-border region around the affected provinces and across international destinations beyond them. On 2 June 2026, the Bunia International Airport in the centre of the outbreak was reopened to commercial traffic [9]. As of 4 June 2026, the DRC has reported 471 laboratory-confirmed cases, 153 suspected cases, and 82 confirmed deaths across twelve health zones in Ituri and North Kivu provinces; Uganda has reported 19 laboratory-confirmed cases. Using the GLEAM (Global Epidemic and Mobility) framework [4,5], this update factors in increased domestic and regional mobility following the airport reopening and expands the source set to include South Kivu and the full Uganda footprint. The top-ranked international destinations (excluding Rwanda and Burundi as regional spillover) are Sumbawanga (TZA, RR 28.1%), Juba (SSD, RR 23.4%), Bukoba (TZA, RR 11.5%), Kisumu (KEN, RR 6.4%), and Dubai (ARE, RR 4.5%). At the regional level, Africa accounts for approximately 85% of conditional international risk, with the Middle East (7.3%), Europe (3.7%), Asia (2.9%), and the Americas (1.3%) sharing the intercontinental tail. The values reported are conditional on at least one international export occurring; the unconditional probability of international export remains small.

1   Executive Summary

Reports #1 to #3 quantified relative importation risk in the immediate cross-border region around the affected provinces and across international destinations beyond them. On 2 June 2026, the Bunia International Airport in the centre of the outbreak was reopened to commercial traffic [9]. This update factors in the resulting potential increase in domestic and regional mobility from the affected areas. The analysis ranks destinations beyond the affected area under the same mobility-based framework used in Reports #1 to #3. In addition, Rwanda and Burundi, the immediate regional neighbours sharing direct overland routes with the affected area, are also excluded from the destination set: their border policy with respect to the current outbreak remains uncertain, and the substantial mobility flow into these neighbours is better characterised as regional spillover than as international dissemination. Relative importation risk (RR) values are therefore renormalised so they sum to one across 208 international destinations beyond the immediate region.

This analysis describes conditional ranking: it does not assert that an international export will occur, but rather, in the event of at least one international export occurring, indicates where it is most likely to be detected. The absolute probability of any single international export remains small.

2   Methods

Mobility data

Global air travel patterns are derived from the International Air Transport Association (IATA) and the Official Airline Guide (OAG), providing passenger-level origin–destination flows between international airports. These data are complemented by short-scale commuting patterns capturing daily movements between adjacent subpopulations, representing the local spread of disease through routine human activity within and across health zones. The modeling approach follows the GLEAM (Global Epidemic and Mobility) computational framework [4,5].

Relative importation risk

For each potential destination Y, the model estimates the probability P(Y) that an infected individual originating in the affected area travels to Y, conditional on at least one exported case occurring. The output is a relative risk distribution across all candidate destinations, normalized so that values represent the share of importation probability assigned to each location.

Renormalization to the international tail · update

Following the 2 June 2026 reopening of the Bunia International Airport [9], this update factors increased domestic and regional mobility from the affected area into the model. The full footprint covers Ituri, North Kivu, South Kivu, and Uganda, reflecting the laboratory-confirmed travel-related case in Bukavu (South Kivu) and the 19 laboratory-confirmed cases in Uganda. As in Reports #1–#3, the model's native output is a relative-risk distribution P(Y) over all candidate destinations, conditional on at least one exported case occurring. To support surveillance prioritization, this report restricts the destination set to non-local international locations, excluding the affected area itself, any other DRC locations, and the immediate regional neighbours Rwanda and Burundi (whose border policy with respect to the outbreak remains uncertain and whose flow is better treated as regional spillover than international dissemination), and renormalizes so the RR values sum to one across 208 international destinations.

3   Regional Distribution

Aggregating relative importation risk by region still shows a concentration in Africa, but the geometry shifts substantially once regional spillover (Rwanda, Burundi) is removed. African destinations now account for approximately 85% of the conditional international risk, driven principally by Tanzania (45%), South Sudan (23%), and Kenya (10%) — the next ring of African neighbours beyond the immediate regional cluster.

The intercontinental tail is more clearly visible than in Report #3 after the regional spillover removal. The Middle East accounts for 7.3% (Dubai 4.5% as the dominant single contribution), Europe for 3.7% (led by the United Kingdom, 1.2%), Asia for 2.9% (India and China together ~2.2%), and the Americas for 1.3% (primarily the United States). The shift reflects the activation of domestic and regional aviation following the Bunia airport reopening, which redistributes mobility flow into nearby destinations rather than the long-haul intercontinental routes that previously transited through Kampala.

4   Destination Analysis

Within the international tail, conditional risk concentrates in a small set of locations. The top-ranked destinations are Sumbawanga (TZA, RR 28.1%), Juba (SSD, RR 23.4%), Bukoba (TZA, RR 11.5%), Kisumu (KEN, RR 6.4%), and Dubai (ARE, RR 4.5%), together accounting for roughly 74% of the conditional international risk. The full top-30 ranking is shown below.

The geographic distribution shown in the world map (Figure 1) reflects country-level aggregate risk. Figure 2 ranks the top ten destination countries, and Figure 3 the top twenty-five destination cities. Bars are coloured by region.

5   Caveats & Limitations

Model scope

The mobility model does not incorporate sociodemographic attributes of travelers (age, economic status, occupation, or pre-existing medical conditions), any of which may modulate both exposure risk at origin and care-seeking behavior at destination. Travel probability within a catchment area is treated as independent of these attributes and of specific location within the catchment.

These estimates apply to traffic from the general population. The importation risk associated with repatriation flights, responder evacuations, or other ad-hoc operational movements is not part of this analysis.

Case importations are modeled as statistically independent events. Real-world events involving multiple related cases (for example, a family cluster traveling together) are counted as a single importation event. To the extent that such clusters are common, the model will under-count the number of distinct exposure events while correctly counting the number of distinct geographic seedings.

Data limitations

Mobility data may not fully capture informal cross-border movement, which is substantial within the immediate cross-border region but is not the focus of this report. For the international tail considered here, the model relies on origin-destination flight data (IATA / OAG). The reopening of the Bunia Airport on 2 June 2026 [9] is factored by resuming mobility from the region, although actual traffic may differ from pre-pandemic baselines.

Epidemiological assumptions

The incubation period of Bundibugyo virus (2–21 days; average ~10 days) constrains the window within which an exported case could reasonably travel while infectious or pre-symptomatic. The model does not predict downstream transmission chains following an importation event: risk estimates reflect the probability of a single importation and do not account for the probability of sustained local transmission in the receiving location.

Conditional vs. absolute risk

The values reported here are conditional on at least one international export occurring. They describe how international exportation probability is distributed across destinations given that an international export happens, not the absolute probability that any specific destination will receive a case. The unconditional probability of international export remains small.

6   References

[1] World Health Organization Regional Office for Africa. Ebola Bundibugyo Virus Disease Outbreak — Democratic Republic of the Congo | Uganda. Weekly External Situation Report 01. Data as of 18 May 2026.

[2] World Health Organization. Epidemic of Ebola disease caused by Bundibugyo virus in the Democratic Republic of the Congo and Uganda determined a public health emergency of international concern. WHO Statement, 16 May 2026.

[3] Centers for Disease Control and Prevention. Ebola Disease: Current Situation. CDC Situation Summary, 18 May 2026.

[4] Balcan D, Gonçalves B, Hu H, Ramasco JJ, Colizza V, Vespignani A. Modeling the spatial spread of infectious diseases: the GLobal Epidemic and Mobility computational model. J. Comput. Sci. 2010;1(3):132–145.

[5] Davis JT, Chinazzi M, Perra N, Mu K, Pastore y Piontti A, Ajelli M, Dean NE, Gioannini C, Litvinova M, Merler S, Rossi L, Sun K, Xiong X, Longini IM, Halloran ME, Viboud C, Vespignani A. Cryptic transmission of SARS-CoV-2 and the first COVID-19 wave. Nature. 2021;600:127–132.

[6] Wamala JF, Lukwago L, Malimbo M, et al. Ebola hemorrhagic fever associated with novel virus strain, Uganda, 2007–2008. Emerg. Infect. Dis. 2010;16(7):1087–1092.

[7] International Air Transport Association (IATA). Passenger Intelligence Services. IATA, 2026.

[8] Official Airline Guide (OAG). Aviation Analytics. OAG, 2026.

[9] Reuters. Congo re-opens airport at the centre of Ebola outbreak. 2 June 2026.