Gene Mapping Yields Clues to Recent Ebola Outbreak

Cross-border movement in West Africa was less than anticipated, research shows

By Robert Preidt

Thursday, June 18, 2015

THURSDAY, June 18, 2015 (HealthDay News) -- New insight into the Ebola outbreak in West Africa has been gained by scientists who analyzed the genetic blueprint -- or genome -- of hundreds of specimens of the deadly virus.

Health officials believe the worst of the epidemic that began in late 2013 is past, but the outbreak is not over.

"Our early work tracked the virus's movements over just three weeks as the outbreak emerged in Sierra Leone. Now with a view of the virus over seven months, we can understand how it has been moving and changing over the long term," study senior author Pardis Sabeti said in a Harvard University news release.

One insight gained is that later in the outbreak, there was very little cross-border exchange of the virus, lead author Danny Park said in the news release.

"That's important, because the three main affected countries -- Sierra Leone, Liberia, and Guinea -- are often described as having 'porous borders' which allowed people to travel back and forth," Park explained.

Cross-border movement may have helped fuel the outbreak in its early stages, but once the epidemic was underway, the virus did not migrate in the ways many had predicted.

"This is very reassuring to know that measures to contain the outbreak at borders can work and allows attention to be focused on within-country movement," Park said.

The study was published June 18 in the journal Cell.

The team also gained insight into how Ebola evolved over the outbreak. Early in the epidemic, it spread rapidly and accumulated many mutations. But as the outbreak continued, the number of mutations slowed.

"Ebola has never been exposed to humans for so long, and through so many transmissions, it has begun to weed out mutations that do not benefit it," Park said.

The many mutations seen early in the outbreak and the evolution documented over the long-term have been observed for other viruses, and the genetic data helps illuminate known evolutionary trends, Sabeti said. "The data just remind us what we have always known, that we must get this viral lineage to zero," he said.

SOURCE: Harvard University, news release, June 18, 2015

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