Several viruses of the family Filoviridae cause severe and frequently fatal viral hemorrhagic fevers in humans. Introduction of filoviruses into human populations is an extremely rare event that most likely occurs by direct or indirect contact with healthy mammalian filovirus hosts or by contact with infected, sick, or deceased nonhuman primates. Filoviruses are highly infectious but not very contagious. Natural human-to-human transmission takes place through direct person-to-person (usually skin-to-skin) contact or exposure to infected bodily fluids and tissues; there is no evidence of such transmission by aerosol or respiratory droplets. Infections progress rapidly from influenza-like to hemorrhagic manifestations and typically culminate in multiple-organ dysfunction syndrome and shock. Treatment of filovirus infections is of necessity entirely supportive because no specific efficacious antiviral agents or vaccines are yet available.
Filoviruses are categorized as World Health Organization (WHO) Risk Group 4 Pathogens. Consequently, all work with material suspected of containing filoviruses should be conducted only in maximal containment (biosafety level 4) laboratories. Experienced personnel handling these viruses must wear appropriate personal protective gear (see “Prevention,” below) and follow rigorous standard operating procedures. The proper authorities and WHO reference laboratories should be contacted immediately when filovirus infections are suspected.
The family Filoviridae includes three genera: Cuevavirus, Ebolavirus, and Marburgvirus (Table 234-1 and Fig. 234-1). The available data suggest that the only known cuevavirus, Lloviu virus (LLOV), and one ebolavirus, Reston virus (RESTV), are not pathogenic for humans. The remaining four ebolaviruses—Bundibugyo virus (BDBV), Ebola virus (EBOV), Sudan virus (SUDV), and Taï Forest virus (TAFV)—cause Ebola virus disease (EVD; International Classification of Disease, Tenth Revision [ICD-10], code A98.4). The two marburgviruses, Marburg virus (MARV) and Ravn virus (RAVV), are the etiologic agents of Marburg virus disease (MVD; ICD-10 code A98.3).
Filoviruses have linear, nonsegmented, single-stranded, negative-sense RNA genomes that are ~19 kb in length. These genomes contain six or seven genes that encode the following seven structural proteins: nucleoprotein, polymerase cofactor (VP35), matrix protein (VP40), glycoprotein (GP1,2), transcriptional cofactor (VP30), secondary matrix protein (VP24), and RNA-dependent RNA polymerase (L protein). Cuevaviruses and ebolaviruses, but not marburgviruses, also encode three nonstructural proteins of unknown function (sGP, ssGP, and Δ-peptide). Filovirions are unique among human virus particles in that they are predominantly pleomorphic filaments but also assume torus- or 6-like shapes (width, ~80 nm; average length, ≥790 nm). These enveloped virions contain helical ribonucleocapsids and are covered with GP1,2 spikes (Fig. 234-2).
TABLE 234-1Filovirus Taxonomy |Favorite Table|Download (.pdf) TABLE 234-1Filovirus Taxonomy
|Current Taxonomy and Nomenclature ||Previous Taxonomy and Nomenclature |
Species Marburg marburgvirus
Virus 1: Marburg virus (MARV)
Virus 2: Ravn virus (RAVV)
Species Taï Forest ebolavirus
Virus: Taï Forest virus (TAFV)
Species Reston ebolavirus
Virus: Reston virus (RESTV)
Species Sudan ebolavirus
Virus: Sudan ...