Prospective Observational Study of the Mortality of Patients With Filovirus Disease

Filoviruses, including Ebola Zaire, Sudan, Bundibugyo, Tai Forest and Marburg virus, are responsible for haemorrhagic fevers with high overall mortality: a recent meta-analysis reports an average case fatality rate of 59%, with extremes of 20 to 90% depending on the epidemic. Between 1976 and 2014, about twenty epidemics of filoviruses diseases (FVD) occurred in Central Africa, without much scientific documentation. The largest ever is an outbreak of Ebola virus disease (EVD) declared in West Africa between 2014 and 2016 (in Guinea, Liberia, and Sierra Leone) and recorded 11,310 deaths for 28,616 cases. Currently, an outbreak of Bundibugyo virus disease (BVD) is active in the Democratic Republic of Congo (DRC) (Ituri and North Kivu provinces) and Uganda.

It was declared a "public health emergency of international concern" by the World Health Organization (WHO) on May 17, 2026. It currently has 399 deaths out of 1333 cases reported as of June 29, 2026, reflecting the scale of the outbreak. Bundibugyo virus (BDBV) was first identified in 2007 in Uganda. The epidemic is only the third documented emergence of BVD, following those observed in Uganda in 2007 and in the DRC in 2012. The lethality of BVD is estimated to be approximately 25%. Genetically, BDBV is different from the most common species, the Zaire Ebola virus (EBOV), in a proportion of about 40%. This genetic distance explains the difficulties in adapting diagnostic approaches (molecular biology) and therapeutic approaches (monoclonal antibodies, direct-acting antivirals, and vaccines) developed for EBOV.

By the incubation period, in the order of 2 to 21 days, and the ease of air travel in the 21st century, we can expect that cases of FVD are diagnosed and treated outside of epidemic areas (in particular the healthcare staff working in epidemic areas and contaminated in a nosocomial way). During previous filovirus epidemics, a very small number of infected people were treated outside the epidemic areas. Therefore, little is known to date about the clinical and biological characteristics and the treatment history of filovirus diseases in patients managed outside the African context.

In this context, it is necessary to set up an observational cohort study of any case of disease with proven filovirus that arrived or was diagnosed in the national territory in order to describe the disease, its clinical course, prognosis, as well as to study its pathophysiology to identify new targets for the diagnosis and curative and preventive treatment.

Knowledge on filovirus diseases acquired during the care of patients with EVD outside of epidemic areas are very fragmented and the absence of biological collections taken from the few patients with EVD in previous epidemics and hospitalized in Europe or the United States did not allow us to describe interactions between the host and the pathogenic species, this being particularly true for rare strains such as the BDBV. Given the genetic distance between species, and that this is the largest epidemic to date caused by the Bundibugyo species, BVD may have clinical, biological, and prognostic features different from other filoviruses.