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Ebola outbreaks before the most recent one have been fairly contained: geographically¹ limited, and just a couple hundred cases. The latest outbreak, though, which started in late 2013 and lasted more than two years, was entirely² different. “There were almost 30,000 cases.” Jeremy Luban, a virologist at the University of Massachusetts Medical School. “You could argue this was the first actual epidemic³.”

Luban and his colleagues studied publicly available data on the evolutionary⁴ “family tree” of the Ebola virus during the latest outbreak—how the strains mutated and changed over time. “And one in particular caught our attention. It arose early in the epidemic, and it’s the only form of the virus that persisted beyond that point.” 

This mutant strain was armed with an alteration⁵ in the protein it uses to enter cells. What Luban’s team found was that the modified protein actually made the strain more infectious to the cells of humans and other primates—but not to other mammals. The study is in the journal Cell. [William E. Diehl et al., Ebola Virus Glycoprotein with Increased Infectivity Dominated the 2013–2016 Epidemic]

Luban says it’s unclear whether this increased infectivity helped drive the outbreak to epidemic proportions. Or whether the length and size of the epidemic simply allowed for more virulent⁶ strains like this one to appear. Still, he says, studying these strains helps us understand how the virus infects—and replicates⁷. “That may help us treat infections in the future, to develop therapies, or to develop vaccines⁸ to block an infection.” In other words: know thy enemy. 

—Christopher Intagliata