Researchers from four countries have used deep sequencing to analyse the full suite of Ebola virus strains present in 78 people diagnosed in Sierra Leone in the ongoing West African epidemic. The outbreak began in February 2014 in Guinea, and health officials had recorded 1,552 deaths as of 28 August, although this is thought to be well below the actual figure.

The study authors report that the current outbreak is caused by a virus variant that separated about ten years ago from viruses responsible for past Ebola outbreaks. This variant has accumulated 341 mutations since then, and 55 more as it spread among the people sampled in this study. In contrast to some past Ebola outbreaks, in which humans repeatedly acquired the virus from animal reservoirs, human-to-human transmission is driving the current outbreak. The researchers hope that the work will inform the design of Ebola diagnostics, vaccines and treatments.

Science http://doi.org/vfk (2014)