Some doctors call it “walking Ebola” – symptoms of the rare Bundibugyo strain appear to worsen slowly, leaving patients sick enough to spread the virus but not so unwell to stop them moving through their communities. The pattern emerging in the Democratic Republic of Congo resonated with virologist Corri Levine, who devoted her doctoral research to Bundibugyo years before it caused the fastest-growing Ebola outbreak on record. Studying the virus in a biocontainment laboratory at the University of Texas Medical Branch, Levine found it replicated more slowly than the Zaire strain responsible for a devastating epidemic that swept West Africa...