This document discusses Ebola virus in Sierra Leone, including: - Ebola diverged from Marburg virus nearly 10,000 years ago and has ancient origins. Exposure to Ebola is very high in some populations in Sierra Leone. - Over 10,000 Ebola cases have been reported to date, though the actual number is estimated to be 2.5x higher due to underreporting. Cases were doubling every 15-20 days. - Genomic sequencing of early Sierra Leone cases revealed the outbreak originated from lineages in Guinea and West Africa. Sierra Leone saw three main genetic clusters of the virus emerge.