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Ebola viruses have for the last forty years been responsible for a number of outbreaks of Ebola virus disease (EVD) in humans (Pattyn et al., 1977), with high case fatality rates typically around 60–70%, but potentially reaching as high as 90% (Feldmann and Geisbert, 2011). The most recent outbreak began in Guinea in December 2013 (Baize et al., 2014; Bausch and Schwarz, 2014) and has subsequently spread to Liberia, Sierra Leone and Nigeria (ECDC, 2014). The unprecedented size and scale of this ongoing outbreak has the potential to destabilise already fragile economies and healthcare systems (Fauci, 2014), and fears of international spread of a Category A Priority Pathogen (NIH, 2014) have made this a massive focus for international public health (Chan, 2014). This has led to the current outbreak being declared a Public Health Emergency of International Concern on the 8 August 2014 (Briand et al., 2014; Gostin et al., 2014; WHO, 2014d).
The Filoviridae, of which Ebolavirus is a constituent genus, belong to the order Mononegavirales. Two other genera complete the family: Marburgvirus, itself responsible for a number of outbreaks of haemorrhagic fever across Africa (Gear et al., 1975; Conrad et al., 1978; Smith et al., 1982; Towner et al., 2006) and Cuevavirus, recently isolated from bats in northern Spain (Negredo et al., 2011). Five species of Ebolavirus have been isolated to date (Kuhn et al., 2010; King et al., 2012); the earliest recognised outbreaks of EVD were reported in Zaire (now the Democratic Republic of the Congo [DRC]) and Sudan in 1976 (International Commission, 1978; WHO International Study Team, 1978). The causative viruses were isolated (Pattyn et al., 1977) and later identified to be distinct species, Zaire ebolavirus (EBOV) and Sudan ebolavirus (SUDV). A third species of Ebolavirus, Reston ebolavirus, was isolated from Cynomologus monkeys imported from the Philippines to a facility in the United States, where they experienced severe haemorrhaging (Jahrling et al., 1990). Whilst serological evidence of infection with this species has been reported in individuals in the Philippines (Miranda et al., 1991), no pathogenicity has been reported beyond primates and porcids (Barrette et al., 2009; Feldmann and Geisbert, 2011). In 1994 a fourth species, Tai Forest ebolavirus was isolated from a veterinarian who had autopsied a chimpanzee in Côte d’Ivoire (Le Guenno et al., 1995), though the virus has not been detected subsequently. The final species, Bundibugyo ebolavirus, was responsible for an outbreak of EVD in Uganda in 2007 (Towner et al., 2008), as well as a more recent outbreak in the DRC (WHO, 2012b).
(From Pigott et al. 2014 - see original paper at http://elifesciences.org/content/3/e04395#sthash.Qa2ZtB4L.dpuf for references cited)