Phylogenetic analysis of initial Ebola virus genomes from the 16th Ebola Virus Disease Outbreak in the Democratic Republic of Congo, September 2025

On 4 September 2025, the Ministry of Public Health, Hygiene and Social Welfare officially declared the 16th Ebola virus disease (EVD) outbreak in the Democratic Republic of the Congo (DRC). As of 13 October 2025, the outbreak is ongoing in Bulape Health Zone, Kasaï Province, where access to appropriate healthcare facilities and resources is limited. Here, we describe the probable index patient and molecular investigations of samples obtained from six suspected EVD patients from the initial outbreak phase. We identified Orthoebolavirus zairense (EBOV) in five samples from different patients. In addition, we performed whole-genome sequencing and generated four complete EBOV genomes. These genomes form a well-supported phylogenetic cluster with genomes from the 1976 Yambuku/Mayinga outbreak. This study suggests a likely new zoonotic spillover event from an as-yet unidentified natural reservoir. Bayesian molecular clock analysis estimates the EBOV variants circulating in Bulape, DRC to have emerged from late July to mid-August 2025. While the close relationship to 1976 EBOV Yambuku/Mayinga genomes is striking, this poses additional challenges on the comprehension of the animal reservoir species.