DR Congo declares an Ebola outbreak in Kasai after 28 suspected cases and 15 deaths

The Democratic Republic of the Congo's Ministry of Health declared an outbreak of Ebola virus disease on 4 September 2025, after laboratory testing confirmed the virus in samples from the Bulape Health Zone of Kasai Province [s1]. As of that date, 28 suspected cases and 15 deaths had been reported — a case fatality ratio of 54% among suspected cases, with four of the deaths in health-care workers [s1].

WHO says it received the initial alert from the ministry on 1 September [s1]. The declaration came three days later, once the National Public Health Laboratory (INRB) in Kinshasa returned results [s1].

What is known about the first cases

The first known suspected case was a pregnant woman at 34 weeks of gestation who was admitted to Bulape General Reference Hospital on 20 August 2025 with fever, bloody diarrhoea, haemorrhage, vomiting and asthenia [s1]. She developed multiple organ failure and died on 25 August [s1]. Two of the health-care workers who had initially been in contact with her developed similar symptoms and also died [s1].

Suspected cases have since been reported from three health areas within the Bulape health zone — Bulape, Bulape Com and Dikolo — and from the neighbouring Mweka health zone [s1]. About 80% of suspected cases are aged 15 years or older [s1].

Five blood samples from five suspected cases and a nasopharyngeal swab from a probable death were shipped to INRB in Kinshasa, arriving on 3 September [s1]. All five samples tested positive for Ebola virus that day by both GeneXpert and polymerase chain reaction assays [s1].

The sequencing result changes how the outbreak is read

Whole genome sequencing suggests the outbreak is a new zoonotic spillover event and is not directly linked to the 2007 Luebo or 2008–2009 Mweka Ebola outbreaks that occurred in the same province [s1]. That distinction matters operationally. A chain traced back to a survivor of an earlier outbreak — through persistent infection in immune-privileged sites such as the eyes, central nervous system or testes, which WHO notes can occur after recovery — would point investigators toward survivor networks [s1]. A fresh spillover points instead toward wildlife contact, and toward a source that surveillance has not yet identified.

Fruit bats of the Pteropodidae family are thought to be the natural hosts of the virus, which enters human populations through close contact with the blood, secretions or organs of infected animals found ill or dead, including bats, primates, forest antelope and porcupines [s2]. Onward spread is then human-to-human, through direct contact with body fluids or contaminated surfaces [s1][s2].

Why health-care workers appear so early in the count

That four of the 15 deaths are health workers is a recognisable pattern rather than an anomaly. WHO notes that health and care workers have frequently been infected while treating Ebola patients, through close contact before infection control precautions are strictly applied — which in practice means before anyone knows Ebola is what they are treating [s2]. Burial ceremonies involving direct contact with the body of someone who has died also contribute to transmission [s2].

The early clinical picture is non-specific: sudden fever, fatigue, malaise, muscle pain, headache and sore throat, followed by vomiting, diarrhoea, abdominal pain and rash [s2]. Bleeding, despite the disease's reputation, is less frequent and tends to occur later [s2]. WHO notes that Ebola can be difficult to distinguish clinically from malaria, typhoid fever, shigellosis and meningitis early on [s2].

The uncertainty in the numbers

The 28 cases and 15 deaths are counts of suspected cases, not confirmed ones — five confirmations had been returned when the figures were compiled [s1]. Suspected-case counts in the opening days of a filovirus outbreak typically move in both directions as testing catches up: some are ruled out, and retrospective investigation adds others. The 54% case fatality ratio should be read the same way. WHO puts the average case fatality ratio for Ebola virus disease at 50%, with outbreak-level ratios ranging from 25% to 90% [s1].

The incubation period runs from 2 to 21 days, typically 7 to 11 [s1]. People are not infectious during incubation and become contagious only with early symptoms, with transmission risk rising as disease severity increases [s1]. That means the shape of the outbreak over the next three weeks will be determined largely by contacts already exposed before the declaration.

Response and risk assessment

Health authorities have activated crisis committees at local and provincial levels, with risk communication and active surveillance under way [s1]. Cases are being isolated with infection prevention and control measures in place, patients are receiving intravenous medication, and contact isolation and tracing are continuing [s1]. WHO is supporting national authorities with risk assessment and investigation and with operational and financial support [s1].

WHO assesses the overall public health risk as high at the national level, moderate at the regional level and low at the global level [s1].

Unlike Sudan virus disease and Bundibugyo virus disease, Ebola virus disease has licensed vaccines and therapeutics [s2]. WHO also emphasises that early intensive supportive care — rehydration and treatment of specific symptoms — improves survival, and that seeking care early can be lifesaving [s2].

What to watch over the coming weeks: how many of the 28 suspected cases are confirmed, whether transmission stays within the Bulape and Mweka health zones, and whether the source of the spillover is identified.

This article is informational and is not medical advice.

Sources

• [s1] World Health Organization, "Disease Outbreak News: Ebola virus disease – Democratic Republic of the Congo," 5 September 2025. https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON580
• [s2] World Health Organization, "Ebola disease" fact sheet. https://www.who.int/news-room/fact-sheets/detail/ebola-virus-disease