Sudan ebolavirus

Discovery and history

Sudan ebolavirus was first identified in 1976 in cotton-factory workers in Nzara and Maridi, southern Sudan (now South Sudan), in an outbreak that occurred almost simultaneously with the Yambuku Zaire ebolavirus outbreak across the border. The two events were initially assumed to share a virus until subsequent serological and genetic work confirmed they were distinct species. The Nzara cluster killed 151 of 284 reported cases (53 percent case-fatality) and established that the Ebola family contained multiple genetically distinct members.

Reservoir (suspected)

Like other ebolavirus species, the natural reservoir is suspected to be fruit bats of family Pteropodidae, though definitive confirmation for Sudan ebolavirus specifically has been elusive. Surveys of bat populations in Uganda and South Sudan have detected ebolavirus antibodies in several species; isolation of live virus has been rare. The spillover pathway is presumed to involve direct or indirect contact with infected bats or with primates and other forest mammals exposed to bat material — consistent with the pattern documented for Zaire ebolavirus.

Geographic distribution

Sudan ebolavirus circulates in Uganda and South Sudan, with no documented natural circulation outside that region. Eight outbreaks have been recorded: Nzara/Maridi 1976, Nzara 1979, Gulu (Uganda) 2000, Yambio (South Sudan) 2004, Bundibugyo (Uganda) 2007 — initially attributed to Sudan ebolavirus before reclassification as a new species — Luwero (Uganda) 2011, Kibaale (Uganda) 2012, and most recently Mubende (Uganda) 2022. Surveillance is uneven; presumed circulation in wildlife continues across the Uganda-South Sudan-DRC border region.

Clinical features

The clinical course mirrors Zaire ebolavirus: a 2-21 day incubation, sudden onset of fever and myalgia, gastrointestinal phase with severe vomiting and diarrhea, and hemorrhagic manifestations in roughly half of severe cases. Aggressive intravenous fluid replacement is again the foundation of supportive care. Case-fatality has ranged from 41 percent (Kibaale 2012) to 71 percent (Nzara 1976), with the recent 2022 Mubende outbreak landing around 47 percent. The absence of licensed therapeutics for Sudan virus means that outcomes still depend largely on the quality and timing of supportive care.

Notable outbreaks

The 2000 Gulu outbreak in northern Uganda (425 cases, 224 deaths) remains the largest Sudan ebolavirus event. It also shaped modern Ebola response: the WHO Global Outbreak Alert and Response Network deployed at scale for the first time, and ring infection control around Lacor Hospital became a template for subsequent outbreaks. The 2022 Mubende outbreak in central Uganda produced 164 confirmed cases and 55 deaths over four months and prompted the first ring-vaccination trial of a candidate Sudan virus vaccine. The earliest 1976 Nzara/Maridi outbreak, occurring within weeks of the parallel Zaire outbreak across the border, was the discovery event for the species.

Prevention

No licensed vaccine or therapeutic exists specifically for Sudan ebolavirus, which is the defining gap in the current outbreak-response toolkit. The candidate vaccines cAd3-SUDV (chimpanzee adenovirus-vectored) and SVABCV-VR (chimpanzee adenovirus + MVA prime-boost) have shown safety and immunogenicity in phase I/II trials and have been deployed under ring-vaccination protocols during the 2022 Uganda Mubende outbreak and the current 2026 PHEIC. Outside of vaccination, the same infection prevention and control principles apply as for Zaire virus: rigorous PPE in healthcare settings, safe-burial protocols, contact tracing, and dedicated Ebola treatment units.

Where Sudan ebolavirus circulates

Documented in the following countries. Click through for country-specific context, active outbreak status, and historical cases.

Related strains

• ZEBOV The most lethal ebolavirus species and the cause of the 2014-2016 West Africa epidemic. Case-fatality rates have ranged from 44 percent to nearly 90 percent across outbreaks.
• BDBV The lowest-mortality ebolavirus species, with case-fatality of 25 to 40 percent. Cause of the 2026 DRC/Uganda PHEIC outbreak and discovered in western Uganda in 2007.
• TAFV The rarest human-pathogenic ebolavirus, with only one documented human case — a Swiss ethologist who survived after a chimpanzee necropsy in 1994.

Synthesized from World Health Organization Ebola fact sheets, U.S. Centers for Disease Control and Prevention Ebola disease pages, the European Centre for Disease Prevention and Control surveillance atlas, and primary epidemiological literature. Not a substitute for individual medical advice. If you have been exposed to a confirmed or suspected case and develop symptoms, contact a healthcare professional immediately.

Continue exploring: complete guide to hantavirus · live outbreak dashboard · global map