A study published Thursday in the online scholarly journal science said generic evidence indicates 14 women were infected at a funeral in Koindu -- a town adjacent to the border between the two countries -- by a traditional healer known for treating illnesses, one of which unknowingly was caused by the Ebola virus.
The study indicates the virus was spread by a "super-spreader" phenomenon, similar to a 2003 incident in which a doctor, dying from the SARS virus, infected nine other guests of a Hong Kong hotel.
The funeral story was known only anecdotally in scientific circles until confirmed by sequencing the viruses of 78 Ebola patients by the Broad Institute of M.I.T. and Harvard.
"It's frightening that a single event could catalyze a whole outbreak, but that's what it looks like happened," said Columbia University researcher Dr. W. Ian Lipkin.
Over 3,000 cases of Ebola have been reported, with over 1,400 deaths. The World Health Organization predicted 20,000 cases could be discovered before the outbreak is curtailed.