(For more on the Ebola outbreak, see EXT7 <GO>.)
Aug. 29 (Bloomberg) -- The largest outbreak of Ebola in human history took hold in Sierra Leone at the burial of a traditional healer, according to a study that shows how the virus is changing as it spreads into West Africa.
While previous outbreaks were found in remote regions nestled through the middle of the African continent, a decade later new strains have emerged, according to a report in the journal Science. The virus hopscotched from Guinea in February to Liberia in March, Sierra Leone in May and Nigeria last month. There is no indication the rampage has slowed, researchers said.
Scientists from Harvard University and the Broad Institute in Cambridge, Massachusetts, used advances in genomics to determine how and when the virus first struck, analyze changes as it passed through patients and track its evolution across West Africa. It likely had a common ancestor with earlier forms of Ebola before diverging in 2004, according to researchers who sequenced 99 Ebola virus genomes collected from 78 patients in Sierra Leone during the first 24 days of the outbreak.
“We’ve uncovered more than 300 genetic clues about what sets this outbreak apart from previous outbreaks,” Stephen Gire, a Harvard scientist, said in a statement. “Although we don’t know whether these difference are related to the severity of the current outbreak, by sharing these data with the research community we hope to speed up our understanding of this epidemic.”
The new form of the virus is “expanding exponentially,” traveling from patient to patient and doubling the number infected every month.
The disease likely reached Sierra Leone via a traditional healer who treated Ebola patients in Guinea and later died. Fourteen women who attended the funeral then came down with the disease. Samples taken first from those women were sequenced in the U.S. to allow researchers to tease apart variants of the virus. Ultimately, the researchers analyzed more than 70 percent of patients in the country from late May to mid June.
Previous outbreaks were fed in part by natural reservoirs of the virus, currently thought to reside in fruit bats. The researchers were unable to find any evidence of such a pool for the current strain, which instead appears to be leaping directly from one patient to the next.
The study found more than 300 genetic changes between the recent cases and previous strains of the disease, providing clues into the origin of the outbreak that may help contain it.
More than 3,000 people have been infected with the virus in this outbreak, and it had killed 1,552 through Aug. 26 since it was first reported in Guinea, according to the World Health Organization. The virus may infect more than 20,000 before it is controlled, the WHO said yesterday. The genetic data is being made public to help scientists working on a treatment. A footnote to the report showed the devastation Ebola is wreaking on those who are most intimately tied to fighting it.
“Tragically, five co-authors, who contributed greatly to public health and research efforts in Sierra Leone, contracted EVD in the course of their work and lost their battle with the disease before this manuscript could be published,” the paper concludes. “We wish to honor their memory.”