Several viruses of the family Filoviridae cause severe and frequently fatal infections in humans. Introduction of filoviruses into human populations is an extremely rare event that most likely occurs by direct or indirect contact with healthy filovirus hosts or by contact with infected, sick, or deceased mammals. Filoviruses are highly infectious but not especially contagious. Human-to-human transmission takes place through direct person-to-person (usually skin-to-skin) contact or exposure to infected bodily fluids and tissues; no evidence of such transmission by aerosol or respiratory droplets in natural outbreak settings is available. Infections progress rapidly from influenza-like to gastrointestinal manifestations and coagulopathy, typically culminating in multiple-organ dysfunction syndrome and shock. The occurrence of primary subclinical infections is controversial, but a small percentage of survivors may be subclinically and persistently infected. Treatment of filovirus infections is entirely supportive in nature because no specific efficacious antiviral agents or vaccines are yet licensed.
Filoviruses are categorized as World Health Organization (WHO) Risk Group 4 Pathogens. Consequently, all work with material suspected of containing replicating filoviruses should be conducted only in maximal containment (biosafety level 4) laboratories, or the viruses should be properly inactivated prior to further analysis in biosafety level 2 laboratories. Experienced personnel handling these viruses must wear appropriate personal protective equipment (see “Control and Prevention,” below) and follow rigorous standard operating procedures. The proper national 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 205-1 and Fig. 205-1). The available data suggest that the only known cuevavirus, Lloviu virus, does not infect humans, and that one ebolavirus, Reston virus, may infect but not cause disease in humans. The remaining four ebolaviruses—Bundibugyo virus, Ebola virus, Sudan virus, and Taï Forest virus—cause Ebola virus disease (EVD; International Classification of Disease, Tenth Revision [ICD-10], code A98.4). The two marburgviruses, Marburg virus and Ravn virus, are the etiologic agents of Marburg virus disease (MVD; ICD-10 code A98.3).
TABLE 205-1Current Filovirus Taxonomy
Filovirus phylogeny/evolution. Bayesian coalescent analysis of representative variants of all known filovirus clades (represented by underlined GenBank accession numbers). The maximal clade credibility tree is shown with the most recent common ancestor (MRCA) at each node. Posterior probability values are shown beneath MRCA estimates in years. Scale is in substitutions/site based on an analysis ...