Studies: Ebola mutated during recent outbreak

The Ebola virus mutated to more effectively infiltrate human cells during the West African outbreak that killed more than 11,300 people between 2013 and 2016.

That’s the finding of two teams of virologists in studies published Thursday in the journal Cell. The scientists identified a mutation that changed the part of the virus that fits into receptors on the host cell.

Mutant versions of this molecular key were “better at fitting into the lock and got into the cell better,” said Jeremy Luban, a virologist at the University of Massachusetts Medical School and the lead author of one of the studies. Once inside the cell, the virus could hijack its reproductive machinery and begin making copies of itself. Within months of the first appearance of this mutated strain, it was able to dominate the epidemic.

According to Luban, “It’s very difficult to prove that a mutation like this is responsible for the severity of the epidemic. … But it would have to be a pretty amazing coincidence.”

The Ebola epidemic that began in Guinea in late 2013 was the biggest in history — 100 times more people were infected than in any previous outbreak. That meant the virus itself had an unprecedented number of opportunities to evolve. Over the course of 28,000 infections, it seemed likely that the virus would pick up a mutation that helped it infect people, which is how it reproduces, and that natural selection would help that mutation spread.

But early analyses of new mutations in the Ebola genome didn’t identify any that appeared to be adaptive. And there were plenty of nonbiological factors to explain the intensity of the outbreak, particularly the poor public health infrastructure in the hardest-hit areas and the delayed international response.

Still, “as virologists we weren’t really convinced” that the virus hadn’t adapted, said Jonathan Ball, the lead author of the other paper and a professor at the University of Nottingham in Britain. “We thought … some of these changes might be affecting the biology of how the virus behaves.”