Sierra Leone’s explosion of Ebola cases in early summer appears to stem from one traditional healer’s funeral at which 14 women were infected, according to scientists studying the blood of victims.

The funeral, which took place in mid-May, constitutes a “super-spreader” event comparable to one in 2003 in a Hong Kong hotel in which one doctor from China dying of SARS infected nine other guests who spread the virus throughout the city and to Vietnam and Canada.

The funeral was in Koindu, a diamond-mining town across the border from Guéckédou in Guinea, where the outbreak is thought to have begun in December, and the healer was known for treating victims of a mysterious illness that turned out to be Ebola.

The funeral’s central role, which local doctors had anecdotally suspected, was confirmed by geneticists at the Broad Institute of M.I.T. and Harvard who sequenced the virus found in 78 patients treated at Kenema Government Hospital in northeastern Sierra Leone, near the borders with Liberia and Guinea, two countries that are also at the heart of the outbreak.

Their study was published online Thursday by the journal Science.

“It’s frightening that a single event could catalyze a whole outbreak, but that’s what it looks like happened,” said Dr. W. Ian Lipkin, a renowned virus hunter at Columbia University, who called the study “a really nice piece of work.”

Image Dr. Sheik Humarr Khan, Sierra Leone’s leading hemorrhagic fever expert, died from Ebola along with four of his other co-authors before the study was published. Credit... Pardis C. Sabeti

The scientists not only found that all 78 had virus traceable to funeral guests, but also showed that the West African Ebola strain was quite different from a strain that has been circulating thousands of miles away in Central Africa since 1976, and that the two probably diverged as far back as 2004.

“No one knows where it’s been during that time,” said Dr. Pardis C. Sabeti, a Harvard geneticist and study co-author.

It might, she added, have circulated in some combination of bats, apes or other forest animals, “or it could have been circulating in humans for 10 years with little or no notice.”

That information is important, experts said, because the diagnostic tests now in use, as well as drugs and vaccines under consideration, are based on the Central African strain and might not work well on this outbreak. For example, a diagnostic test in use now might not give a clear positive if a victim had a low viral load early in an infection.

The study also found that the 78 victims had two variants of the West African strain. The healer might have been infected with two variants from two of her patients, said Stephen K. Gire, another co-author from Dr. Sabeti’s lab. Or someone else at the funeral could have been infectious.