Marburg and Ebola viruses

Abstract

Infection with Marburg and Ebola viruses cause haemorrhagic fevers that are characterized by organ malfunction, bleeding complications, and high mortality. The viruses are members of the family Filoviridae, a group of membrane-enveloped filamentous RNA viruses. Five distinct species of the genus Ebolavirus have been reported; the genus Marburgvirus contains only one species. Both Marburg and Ebola virus diseases are zoonotic infections whose primary hosts are thought to be bats. The initial human infection is acquired from wildlife and subsequent person-to-person spread propagates the outbreak until it is brought under control. Ebola and Marburg viruses are classified as hazard or risk group 4 pathogens because of the very high case fatality rates observed for Ebola and Marburg virus diseases, the frequency of person-to-person transmission and community spread, and the lack of an approved vaccine or antiviral therapy. This mandates that infectious materials are handled and studied in maximum containment laboratory facilities. Epidemics have occurred sporadically since the discovery of Marburg in 1967 and Ebola virus in 1976. While some of these outbreaks have been relatively large, infecting a few hundreds of individuals, they have generally occurred in rural settings and have been controlled relatively easily. However, the 2013–2016 epidemic of Ebola virus disease in West Africa was different, representing the first emergence of the Zaire species of Ebola in a high-density urban location. Consequently, this has been the largest recorded filovirus outbreak in both the number of people infected and the range of geographical spread. Many of the reported and confirmed cases were among people living in high-density and impoverished urban environments. The chapter summarizes the most up-to-date taxonomic status of the family Filoviridae. It focuses on Marburg and Ebola viruses in a historical context, culminating in the 2013–2016 outbreak of Ebola virus in West Africa. Virus biology of the most well-studied member is described, with details of the viral genome and the protein machinery necessary to propagate viruses at the molecular and cellular level. This information is used to build a wider-scale virus–host perspective with detail on the pathology and pathogenesis of Ebola virus disease. The consequences of cell infection are examined, together with our current understanding of the immune response to Ebola virus, leading to a broader description of the clinical features of disease. The chapter closes by drawing information together in a section on diagnosis, ecology, prevention, and control.