The Lancet On Sept 4, 2025, DR Congo declared its 16th Ebola virus outbreak. The epicentre of this outbreak occurred in the Kasai province—the first resurgence in this region since 2008.1 Genomic analysis identified an Ebola virus with more than 99·5% identity to the lineage that was responsible for the first outbreak in Yambuku in 1976.2 Instead of clustering with more recent outbreaks, a pathogen assumed to evolve steadily appears, in part, unchanged for half a century.
Antibodies and RNA fragments have been found in fruit bats, yet no reservoir species has yielded a live virus.3 The Kasai strain’s proximity to the 1976 outbreak, therefore, narrows the plausible explanations of where, and under what circumstances, Ebola endures between epidemics.
One explanation is persistence, in which Ebola virus hibernates in tissue, alternating between replication and dormancy. This has not been shown in wild animals, but the virus has re-emerged in humans 5 years after apparent recovery.4 Lassa virus provides an analogue, causing chronic infection in rodents with shedding that sustains transmission.5 The Kasai sequences raise the possibility that Ebola persists similarly.