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In its largest outbreak, Ebola virus disease is spreading through Guinea, Liberia, Sierra Leone, and Nigeria. We sequenced 99 Ebola virus genomes from 78 patients in Sierra Leone to ~2000x coverage. We observed a rapid accumulation of interhost and intrahost genetic variation, allowing us to characterize patterns of viral transmission over the initial weeks of the epidemic. This West African variant likely diverged from central African lineages around 2004, crossed from Guinea to Sierra Leone in May 2014, and has exhibited sustained human-to-human transmission subsequently, with no evidence of additional zoonotic sources. Because many of the mutations alter protein sequences and other biologically meaningful targets, they should be monitored for impact on diagnostics, vaccines, and therapies critical to outbreak response. [ABSTRACT FROM AUTHOR]

The article discusses research that suggests that outbreaks of Lassa, Marburg, and Ebola hemorrhagic fever viruses in Africa can be attributed to improvements in the diagnosis and detection of common and widespread diseases, rather than evidence of emerging pathogens. It is noted that seroprevalence surveys indicate widespread exposure to these viruses in sub-Saharan Africa, possibly from contact with animal disease reservoirs such as the Mastomys natalensis mouse, fruit bat, and nonhuman primates. Other topics include analysis of the evolutionary divergence of these viruses pointing to ancient origins, genomic analysis of human adaptations to hemorrhagic fever viruses, and viral research at community health clinics in Sierra Leone and Nigeria.