To date, 12 distinct filoviruses have been described 1. The seven filoviruses that have been found in humans belong either to the genus Ebolavirus (Bundibugyo virus (BDBV), Ebola virus (EBOV), Reston virus (RESTV), Sudan virus (SUDV) and Taï Forest virus (TAFV); Fig. 1) or to the genus Marburgvirus (Marburg virus (MARV) and Ravn virus (RAVV)) 2. The WHO International Classification of Diseases Revision 11 (ICD-11) of 2018 recognizes two major subcategories of filovirus disease (FVD): Ebola disease caused by BDBV, EBOV, SUDV or TAFV, and Marburg disease caused by MARV or RAVV. Ebola virus disease (EVD) is defined as a disease only caused by EBOV. This subcategorization of FVD is largely based on the increasing evidence of molecular differences between ebolaviruses and marburgviruses, differences that may influence virus-host reservoir tropism, pathogenesis and disease phenotype in accidental primate hosts 2. Since the discovery of filoviruses in 1967 (reF. 3), 43 FVD outbreaks (excluding at least five laboratoryacquired infections) have been recorded in or exported from Africa 4. The epidemiological definition of outbreak is one or more cases above the known endemic prevalence. For example, the single case of TAFV infection recorded in a setting in which FVD had never been reported before (Côte d'Ivoire) 5 is still considered an outbreak. All FVD outbreaks, with the exception of that caused by TAFV, were characterized by extremely high case-fatality rates (CFRs, also known as lethality). Until 2013, the most extensive outbreak, caused by SUDV, involved 425 cases and 224 deaths (CFR 52.7%) 6. The overall limited numbers of FVD cases (1967-2013: 2,886 cases including 1,982 deaths 4), the typical remote and rural locations of outbreaks and the often delayed announcement of new outbreaks to the international community 7 have prevented the systematic study of clinical FVD in humans. Thus, the commonly used description of FVD was derived either from observation of small groups of patients in care settings that were not well-equipped for diagnosis, treatment and disease characterization, or from observations of even smaller samples, such as individuals who were transferred from Equatorial Africa to Europe and the USA or who fell sick in Europe or the USA after contracting the virus elsewhere. Pathological characterization of FVD via autopsies has been rare 7,8. In the absence of extensive human clinical data, FVD could only be defined further via the use of experimental animal infections 9,10 .