The Ebola virus evolved as it spread through West Africa last year, but its mutation rate did not accelerate as rapidly as some had thought, reveals an analysis of the virus's genetic sequence data.
The data offer reassurance that the scope of the current epidemic did not involve the virus's evolution into a more virulent or deadlier form.
To reach this conclusion, a team led by Wu-Chun Cao, epidemiologist at the State Key Laboratory of Pathogen and Biosecurity in Beijing, sequenced 175 Ebola virus genomes from people who were infected with the virus, including some who died.
The combined data allowed Cao to track how the Ebola virus changed as it spread east to west across Sierra Leone. Ebola entered the country in May and reached the capital city, Freetown, in July.
The analysis found that the virus evolved as it spread to new areas but it did not change at a faster rate than it has in past outbreaks. There is no evidence that Ebola evolved harmful mutations as it spread through Sierra Leone.
"This is just the virus doing what it does," said David Robertson, computational and evolutionary biologist at University of Manchester.
The study appeared in the journal Nature.