Ebola virus disease: the ‘Black Swan’ in West Africa

Abstract

Ebola virus disease (EVD) was first discovered in the Democratic Republic of the Congo in 1976, and by 2013 had caused approximately 20 recorded outbreaks across East and Central Africa. These had been restricted to rural areas and confined to small clusters of villages. In each case containment was achieved within a few months and after fewer than 500 confirmed cases. The world assumed that EVD was too efficient at killing its hosts, doomed to quickly burn out wherever it arose. The 2014 West African outbreak has changed everything. It was the ‘Black Swan’ – the inevitable consequence we did not foresee. By midDecember 2014, there had been over 17,000 reported cases spread across nearly every region in three adjacent countries, and approximately 6,000 people are known to have died. It spread to the US, Mali, Senegal and Nigeria. Cases have been treated across Western Europe. Until early November 2014, there was no sign of a reduction in transmission, and case numbers were rising exponentially. This is still true of Sierra Leone where over one hundred health care workers have died, and there is no certainty the other affected countries will not again see an upsurge in new cases. Estimates of how many people could be affected have varied widely and include up to 1,400,000, or up to 25,000 cases per day by midJanuary 2015. This has increased dramatically since the World Health Organization (WHO) projected a maximum of 20,000 cases in August 2014, highlighting how difficult it is to predict the future epidemic direction, though organisations such as Medecins Sans Frontieres highlighted their concern as early as March 2014. Mathematical modelling is challenging and cannot easily account for conflict, mass movement of people, or breakdown of civil society, but though the very high case numbers may not be reached, one thing is certain: this will be a terrifyingly large outbreak, something never before faced on a global scale.